Pharmacokinetic and behavioural proﬁle
of THC, CBD, and THC+CBD combinatio
n after pulmonary, oral, and subcutaneous
administration in rats and conﬁrmation
of conversion in vivo of CBD to THC
, Libor Uttl
, Marie Balíková
, Rachel R. Horsley
, Pavlína Nováková
, Kristýna Štefková
, Filip Tylš
, Martin Kuchař
Institute of Forensic Medicine and Toxicology, First Faculty of Medicine, Charles University and General
University Hospital in Prague, 121 08 Prague 2, Czech Republic
Department of Analytical Chemistry, Faculty of Science, Charles University, Albertov 6, 128 43 Prague 2,
National Institute of Mental Health, Topolová 748, 250 67 Klecany, Czech Republic
Department of Physiology, Faculty of Science, Charles University, Albertov 6, 128 43 Prague 2, Czech
Faculty of Food and Biochemical Technology, University of Chemistry and Technology Prague, Technická 5,
166 28 Prague 6, Czech Republic
3rd Faculty of Medicine, Charles University, Ruská 87, 100 00 Prague 10, Czech Republic
Received 23 February 2017; received in revised form 12 August 2017; accepted 22 October 2017
CBD to THC
Metabolic and behavioural effects of, and interactions between Δ9-tetrahydrocannabinol (THC)
and cannabidiol (CBD) are inﬂuenced by dose and administration route. Therefore we
investigated, in Wistar rats, effects of pulmonary, oral and subcutaneous (sc.) THC, CBD and
THC+CBD. Concentrations of THC, its metabolites 11-OH-THC and THC-COOH, and CBD in
serum and brain were determined over 24 h, locomotor activity (open ﬁeld) and sensorimotor
gating (prepulse inhibition, PPI) were also evaluated. In line with recent knowledge we
expected metabolic and behavioural interactions between THC and CBD. While cannabinoid
serum and brain levels rapidly peaked and diminished after pulmonary administration, sc. and
oral administration produced long-lasting levels of cannabinoids with oral reaching the highest
0924-977X/&2017 Elsevier B.V. and ECNP. All rights reserved.
Corresponding author at: National Institute of Mental Health, Topolová 748, 250 67 Klecany, Czech Republic.
E-mail address: email@example.com (T. Páleníček).
European Neuropsychopharmacology (]]]])],]]]–]]]
Please cite this article as: Hložek, T., et al., Pharmacokinetic and behavioural proﬁle of THC, CBD, and THC+CBD combination after
pulmonary, oral, and subcutaneous.... European Neuropsychopharmacology (2017), https://doi.org/10.1016/j.euroneuro.2017.10.037
brain levels. Except pulmonary administration, CBD inhibited THC metabolism resulting in
higher serum/brain levels of THC. Importantly, following sc. and oral CBD alone treatments,
THC was also detected in serum and brain. S.c. cannabinoids caused hypolocomotion, oral
treatments containing THC almost complete immobility. In contrast, oral CBD produced mild
hyperlocomotion. CBD disrupted, and THC tended to disrupt PPI, however their combination did
not. In conclusion, oral administration yielded the most pronounced behavioural effects which
corresponded to the highest brain levels of cannabinoids. Even though CBD potently inhibited
THC metabolism after oral and sc. administration, unexpectedly it had minimal impact on THC-
induced behaviour. Of central importance was the novel ﬁnding that THC can be detected in
serum and brain after administration of CBD alone which, if conﬁrmed in humans and given the
increasing medical use of CBD-only products, might have important legal and forensic
&2017 Elsevier B.V. and ECNP. All rights reserved.
Given the on-going research and use of cannabis and
cannabis-derived products for medical purposes, it is parti-
cularly crucial to understand the nature of cannabinoid
interactions within the organism. Even though more than
100 phytocannabinoids have been identiﬁed in cannabis
plants (Bhattacharyya et al., 2010;Englund et al., 2016;
Hanus et al., 2016;Mechoulam et al., 2014), the two major
phytocannabinoids are Δ
-tetrahydrocannabinol (THC) and
cannabidiol (CBD), both of which have been shown to have
distinct therapeutic and adverse effects (Alexander, 2016;
Schubart et al., 2014;Whiting et al., 2015;Zhornitsky and
Potvin, 2012). While THC is the primary psychoactive
constituent of cannabis, CBD is primarily non-psychoactive
and has been shown to attenuate the behavioural and
metabolic effects of THC (Bhattacharyya et al., 2010;
Englund et al., 2013). In relation to this, recent research
on medical cannabis focuses on various THC: CBD ratios in
order to target particular therapeutic requirements. Owing
to the fact that there is great complexity in the nature of
THC - CBD interactions (McPartland et al., 2015;Reid and
Bornheim, 2001;Todd et al., 2016;Zuardi et al., 2012a), the
pharmacokinetics and behavioural effects of THC and CBD,
and especially their combination, across various forms of
administration, are not yet fully described. Furthermore,
the translation between pre-clinical and human data has
frequently been problematic because the routes of admin-
istration typically used by humans for cannabinoids, i.e.,
pulmonary (e.g., smoking, vaporisation); dermal (e.g.,
application of ointment or lotion) and oral (e.g., consump-
tion in food) are not often employed in animal studies.
In humans, pulmonary administration of cannabis pro-
duces the greatest bioavailability of THC, with serum
concentrations peaking within minutes, and subjective
effects apparent almost immediately (Huestis et al.,
1992), similar to intravenous (iv.) administration of THC
(Bhattacharyya et al., 2010;Englund et al., 2016). By
contrast, after oral administration of cannabinoids/cannabis
preparations, the onset of subjective effects is typically
delayed by 30 to 130 min and peak serum THC concentra-
tions are lower and delayed for about 1 –6 hours after
ingestion, sometimes showing two peaks due to
enterohepatic circulation. Due to ﬁrst-pass liver metabo-
lism, higher levels of the psychoactive metabolite 11-
hydroxy-Δ9-tetrahydrocannabinol (11-OH-THC) are also
typical (for review see Huestis, 2007). Compared to pul-
monary, iv. and oral administration of cannabinoids, very
little is known about the kinetics when administered via skin
compartment (transdermal and subcutaneous administra-
tion; Paudel et al., 2010;Stinchcomb et al., 2004).
Whilst THC binds to a number of non-cannabinoid recep-
tors in the brain, the primary mechanism of action of THC
responsible for its psychoactive effects is mediated via
partial agonism at cannabinoid CB
et al., 2012;Mechoulam et al., 2014). It is also the major
mechanism, via which THC mediates its pro-psychotic
adverse effects (Bhattacharyya et al., 2010;Englund
et al., 2013). In rodents, CB
receptor agonists, like THC,
induce what has been termed the “cannabinoid tetrad”
which is characterised by anti-nociception, catalepsy,
hypothermia and suppression of motor activity (El-Alfy
et al., 2010;Katsidoni et al., 2013). The psychotomi-
metic-like effects of THC and other CB
in preclinical experiments focusing on sensorimotor gating
produced inconsistent ﬁndings, with some studies showing
no effects, some a disruption of PPI and others a facilitation
(Gomes et al., 2014;Gururajan et al., 2011;Levin et al.,
2014;Long et al., 2010a;Long et al., 2010b,2013;Malone
and Taylor, 2006;Nagai et al., 2006;Peres et al., 2016).
Unlike THC, CBD lacks signiﬁcant psychotomimetic
effects; rather, it seems to counteract the psychotomimetic
and behavioural effects of THC, as well as showing anxio-
lytic and antipsychotic properties in and of itself
(Bhattacharyya et al., 2010;Englund et al., 2013;Long
et al., 2010b;Morgan et al., 2010;Pertwee, 2008;Schubart
et al., 2011;Varvel et al., 2006). In animal studies, again in
contrast to THC, CBD does not elicit the classic CB
mediated cannabinoid tetrad (in mice) and it produces
minimal disruption of behavioural tasks in humans, monkeys
and rodents (Lichtman et al., 1995;Winsauer et al., 1999).
This is likely because CBD has a low afﬁnity for, and only
weakly antagonises CB
receptors (Pertwee, 2008;
Thomas et al., 1998;Zuardi et al., 2012a,2012b); more
speciﬁcally at CB
receptors it acts as a negative allosteric
modulator (Laprairie et al., 2015). Instead, the major
T. Hložek et al.2
Please cite this article as: Hložek, T., et al., Pharmacokinetic and behavioural proﬁle of THC, CBD, and THC+CBD combination after
pulmonary, oral, and subcutaneous.... European Neuropsychopharmacology (2017), https://doi.org/10.1016/j.euroneuro.2017.10.037
effects of CBD are via negative modulation of endocanna-
binoid tone through the inhibition of fatty acid-binding
proteins (FABPs) which transport endocannabinoids intra-
cellularly to a metabolising enzyme fatty acid amidohydro-
lase (FAAH) (Elmes et al., 2015) and via its inhibitory action
at anandamide transporters (Campos et al., 2013;Rakhshan
et al., 2000;Watanabe et al., 1996). CBD has, however,
further complex pharmacological actions involving other
neurotransmitter systems and receptors (Campos and
Guimaraes, 2009;Campos et al., 2012;Kathmann et al.,
2006;McPartland et al., 2015;Ryberg et al., 2007). At
sufﬁciently high doses (120 mg/kg intraperitoneally in
mice), CBD may also inhibit hepatic microsomal drug
metabolism, which may lead to increased THC levels in
blood owing to delayed hydroxylation of THC to 11-OH-THC.
In consequence, at high doses, CBD can potentiate (rather
than ameliorate) the aforementioned effects of THC
(Bornheim et al., 1995).
The main aim of our study was to evaluate pharmacoki-
netic and behavioural effects of THC and CBD alone, and in
combination, in rats across three routes of administration:
sc., pulmonary and oral. Speciﬁcally, we aimed to compare
24 hour pharmacokinetic proﬁles of the two natural canna-
binoids and their co-administration at a 1: 1 ratio in rat sera
and brains and effects on locomotor behaviour in the open
ﬁeld and sensorimotor gating in the test of prepulse
inhibition of acoustic startle reaction (PPI ASR). The proﬁles
of the psychoactive metabolite 11-OH-THC, and non-psy-
choactive metabolite 11-nor-9-carboxy-THC (THC-COOH)
were also evaluated. From the behavioural perspective we
hypothesised that THC would have inhibitory effects on
locomotion, that it would disrupt sensorimotor gating, and
that CBD would counteract these effects. We also expected
that the THC induced changes might be more pronounced
after oral administration because of the expected presence
of the potent psychoactive metabolite 11-OH-THC (Huestis,
Finally, since THC and CBD are chemically related com-
pounds, it has been reported that under certain (acidic)
conditions, CBD can be cyclised to THC in vitro: a partial
cyclisation of CBD to THC was reported when CBD was
machine smoked with tobacco, most likely due to acidic
conditions produced by the burned tobacco and by the
acidity of simulated gastric ﬂuids (Merrick et al., 2016;
Quarles et al., 1973;Watanabe et al., 2007). More recently,
the important question has been raised as to whether CBD
can also be converted to THC in vivo (Merrick et al., 2016).
Therefore our last aim was to ascertain whether treatment
with CBD (orally, or by any other route) can result in the
presence of THC in serum, and if so, whether this is
accompanied by THC-mediated behavioural effects.
2. Experimental procedures
For all of the experiments, male Wistar rats (Velaz, Czech Republic)
weighing 200–250 g were used. Animals were housed in standard
laboratory cages in the animal facility with controlled temperature
(22 721C), humidity (30–70%), light/dark cycle (6 a.m. lights on /
6 p.m. lights off) and ad libitum access to water and standard diet.
Before testing, the animals were acclimatised to the animal facility
for 7–10 days, and all experiments were performed between 8:00 h
and 13:00 h, during the light phase under standard temperature and
humidity conditions already described. Unless otherwise stated,
experimental groups (drug route) for the behavioural experi-
ments consisted of 10 animals and each subject was tested only
once. Brains and sera of these rats were used also for kinetic
analyses, with 6 animals per experimental group (see Section 2.4).
All of the experiments adhered to the Guidelines of the European
Union (86/609/EU) and the directives of the Czech National
Committee for the Care and Use of Laboratory Animals. Ethical
approval for the studies was obtained from the Czech Ministry of
2.2. Drug preparation and administration
THC and CBD were obtained from THC-Pharm GmbH in a powder
form. For the pulmonary administrations, 20 mg of THC, CBD, or
their combination (THC: CBD at 1: 1 dose ratio) were dissolved in
98% ethanol in a volume of 200 μl and dropped on the metal-wired
liquid pad purchased with the vaporiser and dried for 1 min. New
liquid pads were used for each administration. Cannabinoids were
then delivered via an in-house set-up consisting of a Volcanos
vaporiser and a hermetically closed plastic inhalation box (volume
9.5 L). Vaporisation was held at 226 1C for 45 sec; 4 animals were
kept together in the box and inhaled the vaporised air for 5 min
(including 45 sec of vaporization). Intact animals placed for the
same period of time in the box, without vaporizing, served as
controls. For sc., and oral administration, THC, CBD and THC+CBD
were dissolved in pharmaceutical grade sunﬂower oil (oleum
helanti) and administered at a dose of 10 mg/kg of each drug or a
mixture of 10 mg/kg THC +10 mg/kg CBD in a volume of 0.5 ml/kg,
which was then delivered by sc. injection, or directly to the
stomach by oral gavage. Control animals were administered corre-
sponding amounts of sunﬂower oil as vehicle. For oral administra-
tion, in order to control for effects of stomach contents on
absorption, the rats were denied food for 12 h prior to drug
administration. The doses used in the current study were selected
according to animal and clinical studies in which: 1) THC shows
behavioural locomotor effects and induces psychotic-like symptoms
in animals (El-Alfy et al., 2010;Katsidoni et al., 2013;Nagai et al.,
2006;Wiley and Burston, 2014); 2) doses of CBD that were effective
in humans to treat schizophrenia, have shown some antagonising
effects on THC and have also shown some antipsychotic-like
properties in rodents (Bhattacharyya et al., 2010;Englund et al.,
2013;Gomes et al., 2014;Leweke et al., 2012;Pedrazzi et al.,
2.3. Blood and tissue collection
In order to minimise the number of animals used, the animals from
behavioural experiments were subsequently used for the kinetic
study. The rats were humanely killed at 0.5, 1, 2, 4, 8 and 24 h (in
batches of six) after oral and sc. administration. After pulmonary
administration, samples at two additional timings were also col-
lected at 0 and 15 min after removal from the inhalation box. All
experimental groups for kinetics comprised six animals per time
point for each separate drug x route treatment. Additional animals
had to be used for time points shorter than 1 hour, some of which
came from the control group. To allow an interval between
behavioural testing and kinetics data collection, these animals
remained undisturbed in a home cage for at least two more days
and subsequently they were exposed to inhalation of cannabinoids.
Separated sera and brains were collected and kept at 20 1C until
the toxicological analysis.
3Pharmacokinetic and behavioural proﬁle of THC, CBD, and THC +CBD
Please cite this article as: Hložek, T., et al., Pharmacokinetic and behavioural proﬁle of THC, CBD, and THC+CBD combination after
pulmonary, oral, and subcutaneous.... European Neuropsychopharmacology (2017), https://doi.org/10.1016/j.euroneuro.2017.10.037
2.4. Quantiﬁcation of THC, 11-OH-THC, THC-COOH and
Cannabinoids were determined by an in-house validated and
certiﬁed GC–MS method (certiﬁed by Police Presidium of the CR,
ref. no.: PPR-31123-7/CJ-2015–990530 / evidence no.: 16/2015). A
total of 10 μl of deuterated CBD-d3/THC-d3/ 11-OH-THC-d3 (5 ng/
μl) internal standard solution was added to each 1.0 ml sample of
serum or brain methanol homogenate (5 ml). For brain analysis, 1 g
of brain tissue was homogenised in 5 ml of methanol. Homogenised
brain samples were frozen at 20 1C in an ethanol bath for 10 min
and then centrifuged at 4 200 rpm for 2 min. Supernatant (4 ml) was
placed in a glass tube and evaporated to 200–300 μl. Serum and
brain extracts were diluted with a 4 ml sodium acetate buffer with
a pH of 4.0 (0.01 mol/l). Serum and brain cannabinoids were
extracted with SPE columns (Bond-ELUT, 130 mg, Agilent Technol-
ogies) and eluted with hexan/ethyl acetate (1:4 v/v) and dried
under a nitrogen gas stream in a 400 μl glass insert placed in a
1.5 glass vial. The samples were derivatised with 100 μlof
N-Methyl-N-(trimethylsilyl) triﬂuoroacetamide (MSTFA) for 20 min
at 80 1C. Quantiﬁcation of extracted cannabinoids was performed
by gas chromatography-mass spectrometry (GC–MS) (GC7860/5742C
MSD, Agilent Technologies) using electron impact ionization in the
selective ion mode (CBD: m/z 391; CBD-d3: m/z 394; THC: m/z 386;
THC-d3: m/z 389; 11-OH-THC: m/z 371; 11-OH- THC-d3: m/z 374;
THC-COOH: m/z 371; THC-COOH:-d3: m/z 374). Calibration curve
ranges were prepared by spiking drug-free bovine serum or drug-
free rat brain homogenate for serum and brain analysis, respec-
tively, at concentrations of (i) 2–100 ng/ml CBD, THC, 11-OH-THC
and THC-COOH; (ii) 100–1 000 ng/ml CBD, THC, 11-OH-THC and
THC-COOH. Limits of detection (LOD) and quantiﬁcation (LOQ) were
1 ng/ml and 2 ng/ml, respectively. The spiked samples were
vortexed and treated identically to the experimental samples.
2.5. Behavioural testing
Behavioural testing was performed 5 min after inhalation, 60 min
after sc. administration and 120 min after oral administration of the
cannabinoids and vehicle according to the estimated maximal peak
of cannabinoid serum levels (Huestis et al., 1992), the selection of
which was subsequently conﬁrmed by our kinetic ﬁndings. The
general behavioural testing procedures were identical to our
previous studies (Horsley et al., 2016;Palenicek et al., 2013;
Palenicek et al., 2016), brieﬂy:
Open ﬁeld test: a square black plastic open ﬁeld arena (68 68
30 cm) was placed in a soundproof and diffusely lit room.
Animals were placed into the centre of the arena and the length
and spatial characteristics of their trajectory were registered for
30 min and pre-processed by an automatic video tracking system for
recording behavioural activity (EthoVision Color Pro v. 3.1.1,
Noldus, Netherlands). Locomotor activity was analysed in 5 min
time intervals. The spatial characteristics of locomotor activity
were recorded in 5 5 grid of virtual zones with 16 located
peripherally and 9 centrally. Frequency (f) of line crossings into
different zones of the arena was used to calculate thigmotaxis ( =
) which indicates the probability of appear-
ance in peripheral zones. Time spent in the centre of the arena
) was calculated as a summation of the time spent in all
9 central zones (∑
Prepulse inhibition of acoustic startle response: PPI ASR was
tested in a startle chamber (SR-LAB, San Diego Instruments,
California, USA). Two ventilated startle chambers (SR-LAB, San
Diego Instruments, California, USA) were calibrated to ensure
equivalent stabilimeter sensitivity between the chambers. The rats
were acclimatised to the startle chamber two days before treat-
ment with a short paradigm consisting of 5 min of background noise
(75 dB white noise) and a subsequent presentation of 6 pulse alone
stimuli (125 dB/20 ms). Startle data were not recorded for accli-
matisation. On the day of the test, a total of 72 trials were held
with an inter-trial interval (ITI) of 4–20 s (mean ITI: 12.27 s). Rats
were acclimatised to the startle chamber for 5 min, during which
time a 75 dB background white noise was continuously presented.
Six 125 dB/40 ms duration pulse alone trials were then delivered to
establish the baseline acoustic startle response (ASR) for the
subsequent calculation of habituation. Subsequently, 60 trials were
presented in a pseudorandom order as follows: (A) pulse alone:
40 ms 125 dB; (B) prepulse-pulse: 20 ms 83 dB or 91 dB prepulse, a
variable (30, 60 or 120 ms) inter-stimulus interval (ISI: mean 70 ms),
then 40 ms 125 dB pulse; (C) 60 ms no stimulus. Finally, six pulse
alone (40 ms 125 dB) trials were delivered. Habituation was calcu-
lated by the percentage reduction in startle values from the initial
six baseline trials to the ﬁnal six trials. PPI was calculated as:
[100(mean prepulsepulse trials / mean pulse alone trials) ∗
100]. Mean ASR was derived from the pulse alone trials. The
average startle response (the area under the curve in arbitrary
units, AVG) was used for the calculation of the dependent variable.
Animals with an ASR AVG response lower than 10 were excluded
from further analysis as non-responders.
2.6. Statistical analysis of behavioural data
Analyses of behavioural data used IBM SPSS version 22 or MS Ofﬁce
Excel. In all cases, the criterion for rejection of the null hypothesis
for po0.05, and all tests were two tailed. Factorial and one-way
ANOVAs (Analysis of Variance) were used to analyse the data,
according to the speciﬁc experimental design in use. Where time
blocks was included in the ANOVA (locomotor trajectory data),
pairwise comparisons of the overall behavioural curves were
planned using contrast analyses according to the method described
by (Abelson and Prentice, 1997), otherwise (for PPI, total locomo-
tion, thigmotaxis and T
), independent t-tests were planned to
follow up signiﬁcant main effects or interactions. Where Mauchly's
test of sphericity (repeated measures ANOVA) or where Levene's
test for unequal variances (independent t-tests) were signiﬁcant,
adjusted statistics are reported. For Abelson's contrasts, since a
mixed design was used, the pooled error term and pooled degrees
of freedom were calculated and are reported. Recalculated and
adjusted degrees of freedom are rounded to whole numbers for
2.6.1. Open ﬁeld
An overall total locomotion was analysed by a 4 (drug) 3 (route)
independent ANOVA with drug (THC, CBD, THC +CBD or vehicle) and
route (sc., pulmonary, oral) as independent factors. Locomotor
trajectory data in 5 min time blocks were analysed using a 4 3
6 mixed factorial ANOVA with drug (THC, CBD, THC +CBD or vehicle)
and route (sc., pulmonary, oral) independent factors, and time
blocks (6 5 min) as a repeated measures factor, followed by
Abelson's contrast analyses to compare (within each route) the
characteristic patterns of locomotor effects (across time blocks) of
the different cannabinoids with vehicle, and with one another.
and thigmotaxis data were each analysed using a 4
3 factorial ANOVA with drug (THC, CBD, THC +CBD or vehicle) and
route (sc., pulmonary, oral) as independent factors.
2.6.2. Prepulse inhibition
ASR data were screened for non-responders (startle amplitude
o10); 14 oral THC and THC +CBD rats were excluded on this basis.
As a result, orally administered groups were excluded entirely from
subsequent habituation and PPI analyses, and the oral route was
dropped as a level of the route factor (leaving sc. and pulmonary
administration groups for analysis). Habituation and PPI were
therefore analysed using a 4 2 factorial ANOVA, with drug
T. Hložek et al.4
(THC, CBD, THC+CBD, or vehicle) and route (sc. or pulmonary) as
3.1. Cannabinoid levels in blood and brain tissue
In the case of sc. administration, the concentration of THC was
approximately four times higher and CBD two times lower during
THC+CBD co-administration in both the serum and brain tissue
compared to single cannabinoid administration. Administration by
the sc. route also revealed two peaks, possibly indicative of a two-
compartment model. CBD sc. resulted in a measurable THC serum
concentration but only 4 h and 8 h after dosing (Figure 1).
After pulmonary administration of cannabinoids, their serum
levels peaked just after removal from the inhalation box while the
brain levels peaked at 15 min after dosing, and then gradually
decreased. The pharmacokinetic proﬁle after co-administration of
THC+CBD was not different to the proﬁles of CBD or THC alone. The
maximum brain cannabinoid concentrations were approximately
three times lower in comparison with serum concentrations
Following oral administration each of the cannabinoids or their
combination, both serum and brain levels peaked at 2 h post
administration and with THC alone the brain concentrations
remained high for another 2 h. Serum and brain concentrations of
CBD were approximately two to threefold lower during THC+CBD
co-administration than in the case of administration of CBD alone.
On the contrary, concentrations of THC were approximately two
times higher during THC+CBD co-administration in comparison with
THC alone. Importantly, oral administration of CBD again resulted in
measurable THC serum concentrations along with CBD concentra-
tions, but here were no detectable levels in the brain (Figure 3). To
ﬁnd out whether this was related to the fact that the levels in the
brain were below the limit of detection (LOD) of the method, we
administered an additional two animals with 60 mg/kg of oral CBD,
and the sera and brains were analysed 2 h after administration. The
concentrations of cannabinoids detected were as follows: (A) for rat
1 serum CBD was 990.9 ng/ml and THC 19.1 ng/ml, brain levels
were 1075.9 ng/g for CBD and 33.3 ng/g for THC, (B) for rat 2 serum
CBD was 723.1 ng/ml and THC below the limit of detection, brain
levels were 871.9 ng/g for CBD and 6.8 ng/g for THC. The oral
administration also resulted in a signiﬁcant accumulation of canna-
binoids in brain tissue, which in the case of THC was more than
double the levels in the serum.
The pharmacokinetic proﬁle of 11-OH-THC after each route of
administration reached the highest concentrations after oral admin-
istration; it accumulated in the brain at concentrations of approxi-
mately 200 ng/g, which is comparable to THC brain levels after
vaporisation (Figs. 1–3). It was not detected at measurable levels
after administration of CBD alone.
The non-psychoactive metabolite THC-COOH had a delayed peak
between 4–8 h after administration, remained detectable 24 h later
and had very low levels compared to 11-OH-THC; after pulmonary and
sc. administration it was not detected in the brain tissue (Tab l e 1).
3.2. Behavioural tests
3.2.1. Open ﬁeld
Total locomotion summed across the time blocks (Figure 4) showed
a signiﬁcant main effect of drug, route and a signiﬁcant interaction,
minimum F (2, 18) =13.49, p=0.001. Independent t-tests (within
route) showed after sc. treatment, there was no signiﬁcant
difference between vehicle and each of the cannabinoids, but after
pulmonary treatment, there were signiﬁcant reduction of locomo-
tion after each of the cannabinoids compared to vehicle, minimum t
(18) =2.96, p=0.01. Similarly after oral treatment THC and THC
+CBD signiﬁcantly reduced total locomotion, but on the contrary
Figure 1 Pharmacokinetic proﬁles of CBD, THC and CBD+THC in serum and brain tissue after subcutaneous administration 10 mg/
kg (six rats per time point). n.d. =not detected.
5Pharmacokinetic and behavioural proﬁle of THC, CBD, and THC +CBD
Figure 2 Pharmacokinetic proﬁles of CBD, THC and CBD+THC in serum and brain tissue after pulmonary administration of 20 mg
vaporised per 4 rats, inhalation for 5 min (six rats per time point).
Figure 3 Pharmacokinetic proﬁles of CBD, THC and CBD+THC in serum and brain tissue after oral administration 10 mg/kg (six rats
per time point). n.d. =not detected.
T. Hložek et al.6
CBD increased it, minimum t(18) =3.92, p=0.001. Comparisons
of routes of administration within each drug treatment showed that
THC and THC+CBD orally had signiﬁcantly lower locomotion
compared to sc. and pulmonary administration of these compounds,
by contrast CBD increased locomotion, minimum t(18) =4.36, p=
The analysis of locomotor data in 5 min time blocks (Figure 5)
showed signiﬁcant main effects for blocks (shown as a typical
progressive decline in locomotor activity over 30 min), for drug and
for route, minimum F (2, 108) =13.49, p=0.001. All possible two-
way interactions were signiﬁcant (drug blocks, route blocks,
drug route), minimum F (10, 371) =2.66, p=0.003. The drug
route blocks interaction was also signiﬁcant: F (21, 371) =
3.46, p=0.001. Figure 6 shows characteristics trajectories.
Subsequent contrast analysis between cannabinoids and vehicle
for the sc. route showed marginally signiﬁcant differences between
the behavioural curves of vehicle versus THC and CBD, F (1, 256) =
3.01, p=0.08, and F (1, 256) =3.23, p=0.07, respectively; the
THC+CBD combination did not differ from vehicle and no differ-
ences between the cannabinoids when delivered via the sc. route
Within the pulmonary route, THC was different to vehicle,
contrast F (1, 256) =6.00, p=0.015, but CBD and THC +CBD did
not differ from vehicle. There were no signiﬁcant differences
between CBD versus THC, or CBD versus THC+CBD, although the
difference between THC versus THC+CBD was marginally signiﬁcant
(contrast F (1, 256) =3.03, p=0.08). This was manifested as
slightly higher activity for THC in early blocks, and some minor
ﬂuctuations in responding from the THC+CBD group, whilst requir-
ing comment, does not merit further discussion.
When administered orally, THC showed signiﬁcantly reduced
locomotor responding, which persisted over time compared to
vehicle, contrast F (1, 256) =24.63, p=0.001, and a similar
pattern was shown after THC+CBD, F (1, 256) =22.87, p=0.001.
Even though the total distance travelled was longer in CBD than in
vehicle, the contrasts for behavioural curves were not signiﬁcantly
different. Locomotor activity was also signiﬁcantly reduced under
THC and the THC+CBD combination compared to CBD alone,
minimum contrast F (1, 256) =15.51, p=0.001, and THC and
THC+CBD did not differ signiﬁcantly from one another.
Within drug contrasts of the curves over time showed that for
CBD, there were signiﬁcant differences between routes, where oral
administration induced higher locomotor activity than sc. or
pulmonary administration, minimum contrast F (1, 256) =4.10, p
=0.05. Oral THC and THC+CBD signiﬁcantly reduced locomotion
compared to sc. and pulmonary administration, minimum contrast F
(1, 256) =10.23, p=0.001, and there were no signiﬁcant
differences between the pulmonary and sc. routes.
(Figure 7), there were no signiﬁcant main effects of
drug or route, maximum F (2, 108) =1.02, p=0.37, but there was
Table 1 Pharmacokinetic proﬁles of THC-COOH in serum and brain tissue after subcutaneous, pulmonary and oral
administration of THC (20 mg vaporised per 4 rats, inhalation for 5 min and 10 mg/kg for oral and subcutaneous
administration, six rats per time point). n.d. =not detected.
Time of Sampling
Route 0 min 15 min 0.5 h 1 h 2 h 4 h 8 h 24 h
Subcutaneous serum (ng/ml) –– 1.0 6.3 4.4 11.9 5.4 2.4
brain (ng/g) –– n.d. n.d. n.d. n.d. n.d. n.d.
Pulmonary serum (ng/ml) 1.4 2.0 1.9 2.6 1.6 2.6 3.2 0.9
brain (ng/g) n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
Oral serum (ng/ml) –– 4.1 8.9 15.0 34.7 43.3 17.7
brain (ng/g) –– n.d. 1.5 5.3 15.7 12.8 4.6
Figure 4 Mean trajectory length over 30 min. after subcutaneous, pulmonary and oral administration of vehicle (VEH), THC, CBD,
or THC+CBD. Error bars show 71 S.E.M. Asterisks indicate signiﬁcant differences from corresponding vehicle, po0.05.
7Pharmacokinetic and behavioural proﬁle of THC, CBD, and THC +CBD
a signiﬁcant drug x route interaction, F (6, 108) =3.46, p=0.004.
Whilst within the sc. route, none of the cannabinoids showed
signiﬁcant differences from vehicle, within the pulmonary route,
each of the cannabinoids signiﬁcantly reduced T
, most mark-
edly for THC+CBD, minimum t(18) =2.24, p=0.038. Within the
oral route, THC signiﬁcantly reduced time in the centre compared
to vehicle, t(18) =2.86, p=0.010, but CBD alone, or in
combination with THC did not, maximum t(18) =1.49, p=1.52.
There were no differences between THC or CBD and THC +CBD
when delivered sc. or orally, however, with pulmonary administra-
tion, THC+CBD signiﬁcantly reduced time in the centre compared
to CBD alone, t(18) =3.62, p=0.005, and similarly, THC +CBD
signiﬁcantly reduced time in the centre compared to THC alone, t
(18) =3.73, po0.002. Finally, there were no signiﬁcant differences
between THC and CBD, irrespective of route of administration.
There were signiﬁcant main effects of drug and route on
thigmotaxis, minimum F (2, 108) =3.57, p=0.032, as well as a
signiﬁcant drug route interaction, F (6, 108) =6.28, p=0.001
(Figure 7). Within the sc. route, CBD affected thigmotaxis, reducing
the likelihood of appearance in the periphery compared to vehicle,
t(18) =2.10, p=0.05, but THC and THC+CBD did not. After
pulmonary treatment, THC and CBD alone reduced thigmotaxis
compared to vehicle, minimum t(18) =3.02, p=0.007, but THC
+CBD did not signiﬁcantly affect this measure. Within the oral
route, THC and CBD alone did not signiﬁcantly affect thigmotaxis,
however THC+CBD signiﬁcantly reduced it, compared to vehicle, t
(18) =2.89, p=0.010. When comparing cannabinoids with one
another, there were no differences on thigmotaxis between THC or
CBD versus THC+CBD, when treated sc. and via pulmonary admin-
istration. However after pulmonary administration, THC+CBD
increased thigmotaxis compared to CBD alone and to THC alone,
minimum t(18) =3.42, p=0.003. After oral treatment, THC+CBD
decreased thigmotaxis compared to CBD and THC, t(18) =2.51, p
=0.02, and there were no signiﬁcant differences between THC and
3.2.2. Prepulse inhibition
ASR data were screened prior to analysis for non-responders (ASR o
10) and a number of rats were excluded on this basis, most notably
from the groups that were orally administered THC (before exclu-
sions mean ASR =20.58, SEM =6.69; 5 rats needed excluding) and
THC+CBD (before exclusions mean ASR =9.38 SEM =3.13; 9 rats
required excluding). Given the ﬂoor in responding (where any
further decrease in startle would not be detectable: (Palenicek
et al., 2013)) and the number of exclusions, the oral route was
dropped from subsequent factorial analysis of habituation and PPI
data. After excluding the oral group, ASR analysis showed no
signiﬁcant main effects or interactions, maximum F (3, 64) =
0.71, p=0.55 (Table 2). Likewise, habituation data showed no
signiﬁcant main effects or interactions, maximum F (3, 63) =0.32,
p=0.81. Therefore neither ASR nor habituation showed baseline
differences that might confound interpretation of PPI data.
On PPI there was a signiﬁcant main effect of drug, F (3, 64) =
4.13, p=0.01 (Figure 8), but no signiﬁcant main effect of route, or
drug route interaction. Independent t-tests by drug on the main
effect (irrespective of route) showed that neither THC nor THC
+CBD were different from vehicle (THC was marginally, maximum t
(32) =1.79, p=0.08), but there was a signiﬁcant difference
between CBD and vehicle, t(33) =2.30, po0.05. THC and CBD did
not differ from one another, however, each was signiﬁcantly
different to THC+CBD, minimum t(34) =2.64, po0.01.
Table 2 shows the descriptive statistics for the non-signiﬁcant
interaction, and also includes values (after exclusions) for the
orally administered groups. Independent t-tests were used to
compare useable oral PPI data; these showed that oral CBD did
not differ to oral vehicle, however there were differences between
the oral and the sc. and pulmonary routs, minimum t(18) =2.09, p
The main ﬁndings of the pharmacokinetic experiments were:
1) cannabinoids were best absorbed after oral administra-
tion, after which brain levels were several times higher
compared to sc. and pulmonary administration; 2) pulmonary
administration yielded an almost immediate peak in canna-
binoid levels followed by their rapid elimination; in contrast,
peaks appeared later after sc. and oral administration, and
cannabinoids were still detectable 24 hours later; 3) sc. as
well as oral, but not pulmonary, co-administration of THC
with CBD yielded an increase in serum and brain levels of
THC compared to THC alone; 4) the psychoactive metabolite
11-OH-THC accumulated in the brain tissue compared to sera
Figure 5 Mean trajectory length per 5 min time block over 30
min after subcutaneous (A), pulmonary (B) and oral
(C) administration of vehicle (VEH), THC, CBD, THC +CBD. Error
bars show 7SEM. Asterisks indicate signiﬁcant differences from
corresponding vehicle, po0.05.
T. Hložek et al.8
and its abundance was highest after oral administration; and
5) the non-psychoactive metabolite THC-COOH was detected
with a delayed peak but surprisingly only in very low
concentrations. A novel and partly unexpected ﬁnding was
the presence of THC in sera after oral and after sc.
administration when only CBD alone had been administered.
An additional experiment with high dose of oral CBD (60 mg/
kg) conﬁrmed the presence of THC also in the brain. The
main behavioural effects of cannabinoids were: 1) moderate
locomotor inhibition after pulmonary administration of can-
nabinoids, 2) strong sedation / catalepsy after oral admin-
istration of THC and THC +CBD; 3) mildly elevated
locomotor activity after oral CBD; and 3) CBD disrupted PPI
(main effect irrespective of pulmonary or sc. administration
route) compared to vehicle.
Pulmonary administration is the most typical method of
cannabis consumption in humans as either a recreational
drug or experimental medicine. In accordance with our
current ﬁndings, peak plasma THC concentrations in humans
are usually reached within few minutes after smoking
(Huestis, 2007;Manwell et al., 2014). While serum levels
rapidly decreased, the brain levels, although having a
maximum three times lower than sera, remained high for
one hour after administration. This is consistent with the
ﬁnding that peak behavioural/cognitive effects in humans
appear with a delay compared to peak serum levels
(Huestis, 2007;Manwell et al., 2014). CBD bioavailability
was about two thirds of THC. One possible explanation may
be the different thermodynamics of the two compounds
with CBD having a slightly higher boiling point than THC
(160–180 1Cversus 157 1C, respectively; (McPartland and
Russo, 2001)), which might, in turn, lead to a lower total
amount of vaporised CBD. Pulmonary THC +CBD did not
produce different pharmacokinetic proﬁles for the two
compounds compared to when CBD or THC were adminis-
tered alone. Finally, no THC levels were detected after
pulmonary CBD administration, which is in line with (Quarles
et al., 1973) who reported that CBD did not form Δ
when marijuana cigarettes were smoked either by a human
subject or by a smoking machine without concomitant use of
As expected and contrary to pulmonary administration of
cannabinoids, the oral administration of both compounds
had much slower kinetics with a peak two hours after
Figure 6 Characteristic trajectories after subcutaneous, pulmonary and oral administration of vehicle (VEH), THC, CBD, THC +CBD.
Figure 7 Mean T
(A) and thigmotaxis (B) over 30 min
after subcutaneous, pulmonary and oral administration of
vehicle (VEH), THC, CBD, or THC +CBD. Error bars show 7
SEM. Asterisks show signiﬁcant differences from corresponding
9Pharmacokinetic and behavioural proﬁle of THC, CBD, and THC +CBD
administration. Interestingly, even though peak serum levels
were comparable to pulmonary administration, brain levels
were three to six times higher and remained very high for
four hours, which clearly indicates that compounds are
gradually accumulated into lipophilic brain tissue. This, in
turn, would correspond to the prolonged effects of orally
administered cannabis products. A very interesting ﬁnding is
that despite the reported very low bioavailability of canna-
binoids after oral administration (6–20% for THC and 6–19%
for CBD (Huestis, 2007;Klumpers et al., 2012;Zhornitsky
and Potvin, 2012)), in our case, we saw the best bioavail-
ability compared to both alternative methods of adminis-
tration. The fact that cannabinoids were dissolved in oil and
that our animals fasted before administration may have led
to better bioavailability compared to a situation when pure
compounds, e.g., a solution encapsulated or dissolved in
water, are administered. The very high brain levels were
also reﬂected in the behavioural tests, as discussed below.
There are two very important issues of the oral admin-
istration. Firstly, co-administration of THC+CBD changed
the pharmacokinetic proﬁles of both cannabinoids com-
pared to administration of each cannabinoid separately.
Speciﬁcally, the maximum mean peak serum concentration
of CBD was three times lower during THC +CBD co-admin-
istration than after CBD alone, while the maximum mean
peak concentration of THC was two times higher compared
to THC alone. Similar pharmacokinetic proﬁles were estab-
lished in brain tissue, whereby the maximum peak concen-
tration of cannabinoids was approximately two times higher.
The effect on THC is most likely related to CBD-induced
inhibition of its liver metabolism, since CBD acts as a potent
inhibitor of cytochrome P450 enzymes CYP1A2, CYP2B6,
CYP2C9, CYP2D6 and CYP3A4 (Zhornitsky and Potvin, 2012).
Even though the abundance of the main psychoactive
metabolite 11-OH-THC was several times higher compared
to pulmonary administration, almost no difference in its
concentration was observed between THC alone and the
THC+CBD groups indicating that this particular metabolic
pathway was not affected. The presence of high levels of
this potent metabolite most likely accounted for/added to
the robust behavioural effects observed after oral adminis-
tration. In contrast to THC, the lower CBD levels compared
to CBD alone treatment are difﬁcult to explain. Since CBD is
metabolised by various enzymes at cytochrome P450
(Jiang et al., 2011), one of the possible explanations could
be an induction of CBD metabolism by THC. However we did
not ﬁnd any literature to directly support this. Interestingly,
a very similar ﬁnding has been shown in humans; when same
doses of THC and CBD were co-administered via different
routes of administration, CBD had lower plasma levels
compared to THC (Guy and Robson, 2004;Huestis, 2007).
So we might assume that several metabolic interactions can
occur between THC and CBD and many of these remain to be
identiﬁed. The second important ﬁnding is that administra-
tion of CBD alone resulted in measurable concentrations of
THC in serum, ranging from 2.0 to 68.6 ng/ml. Surprisingly,
with this current dose we did not detect THC in the brain
Table 2 ASR, habituation and PPI: Means (S.E.M.s are shown in italics) for the cannabinoid (THC, CBD, THC+CBD) by route
(subcutaneous, pulmonary, oral). Values reﬂect AVG amplitude, after exclusions where ASRo10 arbitrary units. The values
presented under THC and THC+CBD oral administration (bold and underlined) correspond to reduced number of animals after
exclusion of ASR non-responders; remaining subjects were: n=5 for THC group and n=1 for THC +CBD group.
Measure Route Vehicle THC CBD THC+CBD
ASR (arbitrary units) Subcutaneous 162.57 (36.22) 189.73 (43.51) 132.37 (16.76) 231.33 (57.35)
Pulmonary 112.28 (25.79) 213.06 (47.70) 155.83 (31.25) 146.95 (21.85)
Oral 185.00 (39.75) 35.45 (9.47) 126.33 (22.23) 27.46 (3.63)
Percentage Habituation Subcutaneous 59.93 (7.28) 58.67 (10.13) 60.53 (6.28) 52.65 (1.99)
Pulmonary 60.68 (6.17) 55.96 (.39) 57.68 (6.50) 64.01 (7.48)
Oral 51.71 (10.79) 71.11 (12.01) 44.31 (11.13) 29.07 (32.64)
Percentage PPI Subcutaneous 51.91 (6.61) 39.13 (7.09) 30.23 (8.70) 51.31 (4.74)
Pulmonary 47.36 (6.25) 37.33 (4.54) 35.06 (7.60) 55.05 (5.42)
Oral 30.03 (5.39) 39.37 (18.07) 34.81 (8.12) 19.28 (17.57)
Figure 8 Mean percentage prepulse inhibition (AVG ampli-
tude) for the signiﬁcant main effect of drug treatment (vehicle
(VEH), THC, CBD, or THC+CBD) collapsed across subcutaneous
and pulmonary routes Error bars show 71 SEM Asterisk shows
signiﬁcant difference from vehicle, connecting lines indicate
signiﬁcant inter-cannabinoid differences, po0.05.
T. Hložek et al.10
tissue. This led us to add an additional study with two rats
administered with a high oral dose of CBD (60 mg/kg) after
which the THC was also detected in the brain two hours
after treatment. Therefore it is possible that minimal levels
of THC could have been present in the brain following
treatment with CBD 10 mg/kg, but did not reach the limit of
detection (LOD) of our analytical method. As noted in the
introduction, previous experimental work indicated that
when CBD is degraded in an acidic environment (artiﬁcial
gastric juice), it rapidly cyclises to Δ
et al., 2007). Recently, (Merrick et al., 2016) conﬁrmed
the formation of psychoactive cannabinoids when CBD is
exposed to simulated gastric ﬂuid and also clearly demon-
strated acid catalysed cyclization to Δ
-THC. According to
the ﬁrst study, not only THC but also other related
hexahydrocannabinols have been associated with catalepsy,
hypothermia and antinociception in mice (Watanabe et al.,
After an initial short-lasting and low amplitude peak, sc.
administration of either THC or CBD resulted in relatively
steady serum and brain concentrations. The concentrations
of THC and CBD reached over the experimental interval
were generally an order of magnitude lower than the
respective pulmonary and oral administration of either of
the cannabinoids. Nevertheless, after sc. administration of
THC+CBD, the THC maximum mean peak concentration was
ﬁve times higher and CBD concentration about half the
value than administration of THC or CBD alone in both the
serum and brain tissue. This presumably also indicates a
signiﬁcant inhibition of THC metabolism by CBD, as has been
already discussed for oral administration. Important ﬁnding
is that 11-OH-THC reached almost the same brain levels as
of THC when THC was administered alone. At the same time
these levels were approximately a half of THC levels when
THC+CBD were co-administered indicating that there is an
accumulation of this potent active metabolite in the brain.
Even though we did not observe much behavioural changes,
this may contribute to theoretical psychotomimetic effects
of the combination. Another observation was a second peak
of cannabinoids with a maximum after 8 h for THC and 11-
OH-THC and 4 h for CBD, which was more prominent in the
brain tissue. A theoretical explanation may be the two-
compartment pharmacokinetics model, where the cannabi-
noids are initially released to the blood stream via certain
carrier mechanisms directly after administration, while at
the same time being depot bound in the skin and fat tissue
from which they are subsequently released. Finally, sc.
administration also yielded measurable levels of THC,
indicating that cyclization may also occur in subcutaneous
fat. Again, no measurable brain THC concentrations were
The presence of THC in sera after oral as well as sc.
administration of CBD may have important psychosocial and
forensic consequences. (Merrick et al., 2016) stated that
people who are treated with high CBD doses may theoreti-
cally experience some signs of THC intoxication, e.g.,
sedation, citing child CBD studies on epilepsy. However his
paper induced vigorous opposition from other researchers
against this suggestion (Grotenhermen et al., 2017;Russo,
2017). Whilst we agree that sedation is probably not linked
to THC effects since other cannabinoids and terpenoids are
more likely responsible, however our ﬁndings conﬁrmed the
conversion in vivo of CBD to THC (albeit in rats at doses
several times higher compared to those typically used by
humans). CBD has become widely used in various forms,
including as a popular food supplement and a constituent of
various dermatological preparations, therefore positive test
results for THC cannot be excluded in subjects using these
CBD-based products, with obvious legal ramiﬁcations (e.g.,
the capacity to drive a motor vehicle). Although the levels
of THC seem to be quite low especially in brain tissue, it is
very speculative if they might produce any objective signs
of intoxication in adults even after very high doses of CBD.
Moreover, conversion of CBD to THC in the stomach will very
much depend on the formulation in which the drug is
administered (Perez-Reyes et al., 1973) and we cannot
exclude that the administration of CBD on an empty
stomach might partially contribute to accelerated transfor-
mation of CBD to THC. A support for this can be extra-
polated from human data where the pH of stomach has been
reported to be the lowest in the morning after whole night
fasting (Brooks, 1985). Nevertheless from a forensic per-
spective, in some places around the globe there may be
zero tolerance to THC when driving and/or operating
machines or performing activities requiring increased atten-
tion, thus CBD users may inadvertently break the law, even
though the use of CBD may be legal.
Finally, very low concentrations of THC-COOH were
detected in our samples (THC: THC-COOH ratio approxi-
mately 10: 1). This is surprising, since in humans this
metabolite is the primary non-psychoactive metabolite
formed from THC, typically displaying plasma levels several
times higher than THC, especially in chronic cannabis users
(Balíková et al., 2014;Karschner et al., 2011). We found
only one study investigating at THC-COOH levels in rats
(Sprague-Dawley strain), which was in agreement with our
data and showed similar results. While THC-COOH was
detected in high concentrations in the liver microsomes of
an in vitro study, the in vivo experiments revealed 11-OH-
THC as the major metabolite in the liver homogenates,
while THC-COOH was much lower and only observed in
female rats (Narimatsu et al., 1991). Similarly, the THC:
THC-COOH ratio in Rhesus monkeys was also approximately
20: 1, thereby showing a similar trend as in rats (Ginsburg
et al., 2014). A most recent ﬁnding has shown that in male
and female Sprague Dawley rats, after intraperitoneal
administration of THC and CBD, another important meta-
bolite of THC, cannabinol (CBN) is produced; it especially
occurs after co-administration of THC with CBD. Further-
more, 11-0H-THC and THC-COOH are much more likely to be
detected in female compared to male rats (Britch et al.,
2017). Therefore, signiﬁcant interspecies and sex differ-
ences in the metabolism of THC may underlie this discre-
pancy between rats and other species.
4.2. Behavioural effects
The mild inhibitory effects on locomotion after pulmonary
administration are in line with the reported cannabinoid
tetrad (El-Alfy et al., 2010;Katsidoni et al., 2013). However
the oral administration of THC either alone, or co-adminis-
tered with CBD produced robust locomotor inhibition in the
open ﬁeld which reﬂected profound sedation/catalepsy
11Pharmacokinetic and behavioural proﬁle of THC, CBD, and THC +CBD
(this was also seen in the PPI ASR study, where rats treated
with oral THC or THC+CBD barely startled to unexpected
auditory stimuli). Of interest is that only oral, but not
pulmonary or sc. administration, yielded such robust effects
which indicates that different metabolites might be respon-
sible. In support of this, Marshell et al. (2014) found a lack
of cataleptogenic effect and less pronounced inhibition of
locomotion after pulmonary administration of THC and
synthetic cannabinoids versus intraperitoneal administra-
tion (Marshell et al., 2014). CBD failed to ameliorate the
observed sedation, even though after oral CBD alone
increased locomotion compared to the control group. There
was an effect of oral THC+CBD on the spatial character-
istics of the trajectory; however, we assume that this is
most likely confounded by the robust locomotor inhibition
rather than related to attenuation of exploration or anxiety.
None of the other treatments showed any signiﬁcant effects
either on locomotion or on its spatial characteristics. The
locomotor inhibitory effect ﬁts within the know cannabinoid
tetrad and is presumably related to the high THC brain
concentrations seen with the oral dose, as a dose depen-
dency for THC induced sedation has already been described
(Shi et al., 2005;Wiley and Martin, 2003). On the other
hand, in some studies THC has been shown to have a dose
dependent bidirectional effects i.e., hyperlocomotion in
low doses and hypolocomotion or sedation at high doses (El-
Alfy et al., 2010;Katsidoni et al., 2013). However, none of
the THC treatments produced any sign of increased locomo-
tion even though the brain concentrations varied widely
across different routes of administration. Even though
highly speculative, an exception could be the increase in
locomotion after oral CBD. Low THC levels in the serum
were present in this case and even though they were not
detected in the brain because of the supposed higher LOD of
the analytical method used, these low THC levels could
theoretically be an underlying cause of the mild stimulatory
effects (El-Alfy et al., 2010;Katsidoni et al., 2013). Even
though the increase in locomotion after CBD was surprising,
it has also been recently described in Sprague Dawley rats
(Britch et al., 2017). It is highly unlikely that increased
locomotion under CBD was a result of anxiolysis, since we
saw no evidence for this in our analysis of the spatial
characteristics of locomotor behaviour.
After exclusion of the oral THC treated groups, we did not
observe any signiﬁcant baseline effects on ASR or habitua-
tion that might confound interpretation of effects of drug
and route on PPI ASR. THC marginally disrupted PPI (two-
tailed); it is of note that if one-tailed test would have been
used (to test speciﬁc hypothesis that THC disrupts PPI), it
would result in statistical signiﬁcance (p=0.04). Thus mild
pro-psychotic effects of THC may have been detected. The
disruptive effect of CBD alone was a surprise; usually the
neurobiological basis of cannabinoid induced deﬁcits in PPI,
if present, seems to be attributed to CB1 as well as
dopamine mediated mechanisms (Malone and Taylor, 2006;
Nagai et al., 2006;Tournier and Ginovart, 2014), however in
the case of CBD, with its wide pharmacological action, it
cannot be explained so easily. As stated earlier, literature
ﬁndings on PPI are inconsistent regarding the effects of CB1
agonists (Gomes et al., 2014;Gururajan et al., 2011;Levin
et al., 2014;Long et al., 2010a;Long et al., 2010b,2013;
Malone and Taylor, 2006;Nagai et al., 2006;Peres et al.,
2016). Most likely differences according species and strain,
synthetic versus natural cannabinoids and their potency,
partial versus full agonism underlie such inconsistencies
(Levin et al., 2014;Malone and Taylor, 2006;Peres et al.,
2016). This also seems to be the truth for CBD alone e.g.,
(Gururajan et al., 2011;Long et al., 2010b). Interestingly,
even though CBD alone induced disruption in the PPI, when
co-administered with THC, there was no difference from
vehicle controls, and signiﬁcant PPI improvement compared
to both THC as well as CBD. This seems to be in accordance
with CBD's capacity to reverse PPI deﬁcits in various rodent
models of psychosis (Gomes et al., 2014;Gururajan et al.,
2011;Levin et al., 2014;Nagai et al., 2006;Pedrazzi et al.,
2015;Peres et al., 2016) and might lead to the conclusion
that a modest antipsychotic-like effect of CBD on THC
induced deﬁcit was observed.
In conclusion, in contrast to our predictions, CBD had only
an isolated antagonising effect on THC induced sensorimo-
tor deﬁcits, while it left other THC behavioural effects
unaffected and alone it produced sensorimotor gating
disruption. The present study revealed remarkable differ-
ences between cannabinoid pharmacokinetics in relation to
their route of administration and it also reveals important
pharmacokinetic/metabolic interactions of co-administra-
tion of the two main constituents of cannabis, however
these interactions were manifested only marginally in the
behavioural tasks. Contrary to other studies, we observed
good bioavailability of cannabinoids after oral administra-
tion in an oil solution, which will have applications in the
development of formulas with high therapeutic efﬁcacy.
However, the detection of THC in the blood stream after
oral and sc. administration of CBD alone, if conﬁrmed in
humans, may affect the development of therapeutic and
medical CBD products as well as having potential legal and
Role of Funding source
Funding for this study was provided by projects MICR
VG20122015080, VI20172020056, MHCZ—DRO (NIMH-CZ,
00023752), European Regional Development Fund
(ED2.1.00/03.0078), and LO1611 from the MEYS under the
NPU I program, 260388/SVV/2017 and PROGRES Q35. These
institutions had no further role in the study design; in the
collection, analysis and interpretation of data; in the
writing of the report; or in the decision to submit the paper
TomášHložek and Marie Balíková performed the analytical labora-
tory analyses and their subsequent evaluation as well as writing the
TomášPáleníček designed the whole study and experimental
protocol and participated in the behavioural and pharmacokinetic
experiments and writing the manuscript.
Authors Libor Uttl, LukášKadeřábek, Eva Lhotková, Filip Tylš,
Pavlína Nováková, Klára Šíchová, Kristýna Štefková and Martin
T. Hložek et al.12
Kuchařperformed the behavioural experiments, pharmacokinetic
experiments and all contributed to writing and approving the
present manuscript, Rachel Horsley contributed mainly with the
statistical analysis of the data and writing of the manuscript.
Conﬂict of Interest
All of the authors declare that they have no conﬂicts of
The authors would like to thank Craig Hampson, BSc. (Hons) for
helpful comments and language correction.
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