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ORIGINAL RESEARCH
published: 11 February 2020
doi: 10.3389/fvets.2020.00051
Frontiers in Veterinary Science | www.frontiersin.org 1February 2020 | Volume 7 | Article 51
Edited by:
Deirdre P. Campion,
University College Dublin, Ireland
Reviewed by:
Colm B. Collins,
University College Dublin, Ireland
Mario Giorgi,
University of Pisa, Italy
*Correspondence:
Dana Vaughn
dana.vaughn@canopygrowth.com
Specialty section:
This article was submitted to
Veterinary Pharmacology and
Toxicology,
a section of the journal
Frontiers in Veterinary Science
Received: 29 October 2019
Accepted: 21 January 2020
Published: 11 February 2020
Citation:
Vaughn D, Kulpa J and Paulionis L
(2020) Preliminary Investigation of the
Safety of Escalating Cannabinoid
Doses in Healthy Dogs.
Front. Vet. Sci. 7:51.
doi: 10.3389/fvets.2020.00051
Preliminary Investigation of the
Safety of Escalating Cannabinoid
Doses in Healthy Dogs
Dana Vaughn*, Justyna Kulpa and Lina Paulionis
Canopy Animal Health, Canopy Growth Corporation, Toronto, ON, Canada
Objective: To determine the safety and tolerability of escalating doses of three cannabis
oil formulations, containing predominantly CBD, THC, or CBD and THC (1.5:1) vs.
placebo in dogs.
Design: Randomized, placebo-controlled, blinded, parallel study.
Animals: Twenty healthy Beagle dogs (10 males, 10 females).
Methods: Dogs were randomly assigned to one of five treatment groups (n=
4 dogs per group balanced by sex): CBD-predominant oil, THC-predominant oil,
CBD/THC-predominant oil (1.5:1), sunflower oil placebo, medium-chain triglyceride oil
placebo. Up to 10 escalating doses of the oils were planned for administration via
oral gavage, with at least 3 days separating doses. Clinical observations, physical
examinations, complete blood counts, clinical chemistry, and plasma cannabinoids were
used to assess safety, tolerability, and the occurrence of adverse events (AEs). AEs were
rated as mild, moderate, or severe/medically significant.
Results: Dose escalation of the CBD-predominant oil formulation was shown to be as
safe as placebo and safer than dose escalation of oils containing THC (CBD/THC oil or
THC oil). The placebo oils were delivered up to 10 escalating volumes, the CBD oil up
to the tenth dose (640.5 mg; ∼62 mg/kg), the THC oil up to the tenth dose (597.6 mg;
∼49 mg/kg), and the CBD/THC oil up to the fifth dose (140.8/96.6 mg CBD/THC; ∼12
mg/kg CBD +8 mg/kg THC). AEs were reported in all dogs across the five groups and
the majority (94.9%) were mild. Moderate AEs (4.4% of all AEs) and severe/medically
significant AEs (0.8% of all AEs) manifested as constitutional (lethargy, hypothermia) or
neurological (ataxia) symptoms and mainly occurred across the two groups receiving oils
containing THC (CBD/THC oil or THC oil).
Conclusions and clinical significance: Overall, dogs tolerated dose escalation
of the CBD oil well, experiencing only mild AEs. The favorable safety profile of 10
escalating doses of a CBD oil containing 18.3–640.5 mg CBD per dose (∼2–62 mg/kg)
provides comparative evidence that, at our investigated doses, a CBD-predominant oil
formulation was safer and more tolerated in dogs than oil formulations containing higher
concentrations of THC.
Keywords: cannabinoids, CBD—cannabidiol, THC—tetrahydrocannabinol, safety, adverse events, canine
Vaughn et al. Cannabinoid Safety in Dogs
INTRODUCTION
As a result of changing cannabis regulatory frameworks and
social perceptions globally, there is a renewed interest in
the potential therapeutic properties of cannabinoids across
multiple stakeholders, including the veterinary community.
Currently, there are no authorized veterinary drugs containing
cannabinoids in the United States (U.S.) or Canada and state
or federal laws legalizing the use of medical cannabis in
either jurisdiction do not apply to uses in animals (1,2).
Notwithstanding these restrictions, over half (55%) of U.S.-based
veterinarians who responded to a 2018 online survey had clients
inquire weekly or monthly about the use of CBD products in
animals (3). Online surveys also provide data that pet owners in
the U.S. and Canada have purchased cannabis products for their
pets most commonly for the management of pain, inflammation,
and anxiety (4,5). The evidence suggests there is a growing
interest in the potential therapeutic uses of cannabinoids in
companion animals.
While there are existing reviews on the safety and toxicology
of cannabinoids, namely CBD (6–8) and THC (9), the data
are primarily based on studies conducted in rodents and
humans. Existing data suggest that there are differences in
the metabolism of cannabinoids across species, with different
CBD/THC metabolic profiles observed across rodents, dogs,
monkeys, and humans (10–12). Not surprisingly, differences
in the behavioral/physiological effects of cannabinoids across
species have also been reported (11,13).
While minimal, there are published data on the safety
and efficacy of cannabinoids in companion animals. Dogs
have been used in the course of developing the drug safety
profile of CesametTM (nabilone, a synthetic THC; oral) and
Sativex R
(a combination of plant-based CBD and THC; buccal
spray), both approved drugs in the U.S. and/or Canada for
chemotherapy-induced nausea and vomiting (CesametTM), or
spasticity or pain in multiple sclerosis or advanced cancer
(Sativex R
) (14,15). Published studies in dogs also exist on
the pharmacokinetics of CBD (oral; 2–12 mg/kg) or THC
(oral; 1.5 mg/kg) (16–19) and on the safety and/or efficacy of
orally administered CBD (17,20,21) or cannabis extracts (11)
for 4–56 weeks.
The primary objective of this study was to determine the
safety of three cannabis oil formulations, predominant in CBD,
THC, or CBD and THC (1.5:1) in dogs. Since a hallmark
dosing strategy for cannabis initiation is to “start low and go
slow” so as to avoid AEs associated with THC (22), a slow
upward dose titration was used. A secondary objective was to
determine blood levels of CBD, THC, and their metabolites,
namely 7-carboxy-CBD (7-COOH-CBD) and 11-hydroxy-THC
(11-OH-THC) at higher dose levels of CBD (>50 mg/kg) and
THC (>30 mg/kg).
MATERIALS AND METHODS
Study Design
The study was randomized, placebo-controlled, and blinded.
Twenty-four healthy Beagle dogs were acclimated to study
TABLE 1 | Dose volumes and CBD/THC quantities delivered to dogs across treatment groups.
In medium-chain triglyceride oil In sunflower oil
Dose No. Placebo—MCT oil (n=4) CBD oil (n=4) THC oil (n=4) Dose No. Placebo—SF oil (n=4) CBD/THC oil (n=4)
Vol (mL) Vol (mL) CBD (mg) THC (mg) Vol (mL) CBD (mg) THC (mg) Vol (mL) Vol (mL) CBD (mg) THC (mg)
1 0.5a1 18.3 0.7 1 NDb24.9 1 2.5a2.5 17.6 12.1
2 1a2.5 45.8 1.7 2.5 *b62.3 2 5a5 35.2 24.2
3 2.5 5 91.5 3.5 3.3 * 82.2 3 10 10 70.4 48.3
4 5 7.5 137.3 5.2 4.4 * 109.6 4 15 15 105.6 72.5
5 10 10 183.0 6.9 5.8 * 144.4 5 20 20c140.8 96.6
6 15 15 274.5 10.4 7.7 * 191.7 6 25 - - -
7 20 20 366.0 13.8 10.2 * 254.0 7 30 - - -
8 25 25 457.5 17.3 13.5c* 336.2 8 35 - - -
9 30 30 549.0 20.7 18c* 448.2 9 40 - - -
10 35 35 640.5 24.2 24c* 597.6 10 45 - - -
(-), doses not administered; AE, adverse event; CBD, cannabidiol; MCT, medium-chain triglyceride; ND, not detected; SF, sunflower; THC, delta-9-tetrahydrocannabinol; Vol, volume.
aPlacebo controls were on a dosing schedule such that two placebo doses were administered prior to the start of test formulation dosing. This was to ascertain tolerability to escalating volumes.
bCBD was “not detected” in the cannabinoid analysis (mg/mL) of the THC oil formulation; the symbol (*) indicates that CBD quantities at higher volumes of the formulation are unknown.
cn=3 dogs.
Frontiers in Veterinary Science | www.frontiersin.org 2February 2020 | Volume 7 | Article 51
Vaughn et al. Cannabinoid Safety in Dogs
TABLE 2 | Corresponding range of mg/kg cannabinoid doses achieved in dogs across groups.
CBD oil THC oilaCBD/THC oil
BSN weight rangeb9.9–10.9 kg 11.4–13.3 kg 10.5–12.5 kg
Dose No. CBD (mg/kg) THC (mg/kg) THC (mg/kg) CBD (mg/kg) THC (mg/kg)
1 1.7–1.8 0.06–0.07 1.9–2.2 1.4–1.7 0.97–1.2
2 4.2–4.6 0.16–0.17 4.7–5.5 2.8–3.4 1.9–2.3
3 8.4–9.2 0.32–0.35 6.2–7.2 5.6–6.7 3.9–4.6
4 12.6–13.9 0.48–0.53 8.2–9.6 8.4–10.1 5.8–6.9
5 16.8–18.5 0.63–0.70 10.9–12.7 11.3–13.4 7.7–9.2
6 25.2–27.7 0.95–1.1 14.4–16.8 - -
7 33.6–37.0 1.3–1.4 19.1–22.3 - -
8 42.0–46.2 1.6–1.7 25.3–29.5 - -
9 50.4–55.5 1.9–2.1 33.7–39.3 - -
10 58.8–64.7 2.2–2.4 44.9–52.4 - -
(-), doses not administered; BSN, baseline.
aCBD was not detected in the THC oil formulation; as such, mg/kg CBD dosing not applicable.
bWeight range of dogs and absolute quantity of cannabinoids per dose (Table 1) were used to calculate mg/kg dose.
conditions for 24 days prior to treatment allocation. Twenty
healthy adult purpose-bred Beagle dogs (age range =3.0–7.8
years; weight range =10–14 kg) were randomized to one of
five treatment groups with four dogs per group (two males,
two females): (i) CBD-predominant oil; (ii) THC-predominant
oil; (iii) CBD/THC-predominant oil (1.5:1); (iv) medium-chain
triglyceride (MCT) oil placebo; or (v) sunflower (SF) oil placebo.
Up to 10 escalating doses of the oils were planned for
administration (Table 1), with at least 3 days separating doses.
An absolute quantity of cannabinoids (mg) (Table 1) was
administered to the dogs in each treatment group; as such, the
resultant mg/kg cannabinoid dose slightly varied within each
group due to body weight differences (Table 2).
Two different placebo oils were used since the cannabinoid
oils included either SF or MCT oil as solvents. Moreover,
the amounts delivered across the two placebo oils differed
to match the volumes administered with the cannabinoid
oils. The dosing schedule of the placebo oils was such
that two placebo doses were administered prior to the
start of cannabinoid oil dosing to ascertain tolerability to
increasing volumes.
Treatments were administered to fasted dogs by oral
gavage. Each cannabinoid or placebo oil administration
was followed by a 10 mL water flush to ensure full
uptake. A small wet meatball was given immediately
after dosing to disrupt negative association with repeated
oral gavage. If an animal was observed vomiting within
30 min of test or placebo administration, the dose
was re-administered.
Randomization and Treatment Allocation
Randomization was stratified by sex and conducted using
a random number generator in Microsoft EXCEL R
2016
(Microsoft Corporation, Redmond, WA). Cannabinoid and
placebo oil formulations were also randomly assigned a code
name using a random number generator in Microsoft EXCEL R
2016. Once the dogs were assigned to a group (Groups 1
through 5), the study coordinator randomly allocated each
group to a coded product by drawing lots. All technicians
collecting data and administering the investigational products
were blinded to treatment allocation. All bottles containing
the cannabinoid or placebo oil formulations were over-labeled
with opaque white labels. Information about treatment groups
and their respective treatment conditions were securely kept
in the VivoCore Inc. archive room for the duration of
the study.
Description of Interventions
The cannabinoid oils (CBD-, THC-, or CBD/THC-predominant
oils) and placebo oils (SF or MCT oils) were acquired from
Tweed Inc. (Smiths Falls, ON, Canada) and stored between
19.6 and 21.9◦C. The cannabis plants used to prepare the
cannabinoid oils were grown indoors under tightly controlled
environmental conditions. Within one lot, all plants were
genetically identical. Upon harvest, plant material was trimmed,
dried, and extracted. Extraction was performed by super-
critical carbon dioxide, and the extracted resin was diluted
with a food-grade oil (SF or MCT oil) to the target
concentration: 18.3 mg/mL CBD in the CBD-predominant
oil, 24.9 mg/mL THC in the THC-predominant oil, and
7.0 mg/mL CBD +4.8 mg/mL THC in the CBD/THC-
predominant oil.
An independent laboratory (RPC, Fredericton, NB) analyzed
the composition of the cannabinoid oil formulations using
validated methods. Levels of phytocannabinoids and terpenes in
the oil formulations are outlined in Table 3. Solvent extraction
and high-performance liquid chromatography with diode-array
detection (HPLC-DAD) were used for cannabinoid analyses
(accuracy: 90–113%; precision: 5.6–12.8%). Solvent extraction
and gas chromatography/mass selective detector (GC-MSD)
were used for terpene analyses (accuracy: 74–106%; relative
standard deviation: 3.2–9.4%).
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Vaughn et al. Cannabinoid Safety in Dogs
TABLE 3 | Select cannabinoid and terpene analysis of the cannabis oil
formulations.
Constituent CBD oil (with
MCT oil)
THC oil (with
MCT oil)
CBD/THC oil
(with SF oil)
Cannabinoids (mg/mL)a
CBD 18.3 ND 7.0
Delta-9-THC 0.7 24.9 4.8
CBDA 0.6 ND <RL
Delta-9-THCA ND <RL <RL
CBG <RL 2.5 <RL
CBGA ND ND <RL
CBN ND 1.3 <RL
CBC 0.8 1.5 <RL
Terpenes (%) 21 terpenes
below RL
(0.01%)b
Caryophyllene
(0.02%);
remaining 8
terpenes below
RL (0.01%)c
9 terpenes
below RL
(0.01%)c
CBC, cannabichromene; CBD, cannabidiol; CBDA, cannabidiolic acid; CBG,
cannabigerol; CBGA, cannabigerolic acid; CBN, cannabinol; MCT, medium-
chain triglyceride; ND, not detectable; RL, reporting limit; SF, sunflower; THC,
tetrahydrocannabinol; THCA, tetrahydrocannabinolic acid.
aRL was 0.5 mg/mL.
bTwenty-one terpenes were specifically measured: alpha pinene, beta pinene, myrcene,
limonene, terpinolene, linalool, terpineol, caryophyllene, humulene, 3-carene, cis-
ocimene, eucalyptol, trans-ocimene, fenchol, borneol, valencene, cis-nerolidol, trans-
nerolidol, guaiol, alpha-bisabolol, sabinene. RL was 0.01%.
cNine terpenes were specifically measured: alpha-pinene, beta-pinene, myrcene,
limonene, terpinolene, linalool, terpineol, caryophyllene, humulene. RL was 0.01%.
Subject Selection
The purpose-bred animals were acquired from a colony at
VivoCore Inc. (Fergus, ON, Canada). The inclusion criteria
for the study were good general health as determined by the
veterinarian; stable weight over a 10-day period preceding
study start and a weight of 9–15 kg; and, under 8 years of
age. Exclusion criteria were pregnant or lactating dogs; use of
medications or supplements during the course of the study;
receipt of cannabinoid or cancer-related therapies in 2 months
preceding study start; receipt of any test substance within a
month prior to study start; existing or a history of cancer, blood-
or immunology-related disease or other chronic morbidity
(including open wounds, psoriatic or allergic skin conditions,
chronic diarrhea, chronic oral gum or tooth disease, or
cardiovascular disease).
Animal Care
The dogs were individually housed in stainless steel metabolic
cages (height, width, depth =75 ×90 ×102 cm) and those in the
same treatment group were exercised together. Environmental
controls for the animal housing area were electronically set to
maintain a temperature of 18.7–26.2◦C and a 12-h light/dark
cycle. Animals were fed a standard commercial dry canine diet
in stainless steel bowls (Purina ProPlan Savor Adult—Chicken
and Rice Formula) once daily, 7–10 h after dosing. Food was left
for 1 h and the food quantity offered (1.25–2.75 cups) was based
on body weight. Water was available ad libitum in stainless steel
bowls. Upon study completion, animals were returned to their
colony at VivoCore Inc.
Measurable Outcomes
Throughout the study period, food consumption and 24-h
activity (Mini-Mitter R
Actiwatch-64 R
; Mini-Mitter Co., Inc.,
Bend, OR) were measured daily and animal health observations
occurred twice daily. Body weights were collected throughout the
acclimation period, once during the study period, and once upon
study completion. Following administration of the cannabinoid
or placebo oils, animals were monitored up to 9 h post-dose
for body temperature (measured rectally), respiration rate (by
observation), and heart rate (stethoscope). Observations of the
animals were also conducted every 1–3 h post-dosing through
the first 9 h and then at 12 and 24 h. Subjects were observed for
any signs that would not be expected in normal dogs and for
the occurrence of AEs. Experienced veterinary technicians and/or
a licensed veterinarian conducted the clinical observations and
physical assessments.
AEs were rated for severity as (i) mild—activities of daily
living (ADL) not impacted and no intervention indicated; (ii)
moderate—ADL moderately limited (non-invasive intervention
may be indicated); or (iii) severe/medically significant—ADL
significantly limited (23). If one dog in a treatment group
experienced a severe/medically significant AE, no further
treatments were administered to that dog. If two dogs in the same
treatment group experienced severe/medically significant AEs,
subsequent treatments ceased for all dogs in that group.
Blood Collections and Analyses
For analysis of Complete Blood Count (CBC) and clinical
chemistry, 4 mL of blood was drawn by direct venipuncture
from a cephalic or jugular vein; 2 mL was placed into an
evacuated serum separator tube (SST) and another 2 mL
into an evacuated K2EDTA tube. These blood collections
occurred during acclimation (baseline), mid-study (after five
doses of placebo oil, and three doses of cannabinoid oils),
and 7 days following the final dose of the cannabinoid or
placebo oils. Additionally, they occurred 24 h following the
final dose of the cannabinoid oils. With the occurrence of
a severe AE, blood was drawn immediately, and 24 h and 7
days thereafter.
For analysis of CBD, THC, and their metabolites (7-COOH-
CBD and 11-OH-THC), 2 mL of blood was drawn and placed
into an evacuated K2EDTA tube. These blood collections
occurred before and after the ninth dose of the CBD oil and THC
oil (i.e., pre-dose, and at 1, 2, 4, 6, and 24 h post-dose). These
blood collections also occurred 7 days following the final dose of
the cannabinoid or placebo oils.
Blood in the evacuated SSTs was allowed to clot for a
minimum of 30 min but no more than 1 h following collection,
then was centrifuged at 1,525–1,992 relative centrifugal force
(rcf) at 20◦C for 10 min. K2EDTA tubes were centrifuged at
2,800–3,000 revolutions per minute (rpm) for 10 min at 4◦C. The
SSTs and K2EDTA tubes were stored at 2 to 8◦C and on the same
day as blood collection were transported to Antech Diagnostics
(Mississauga, ON) for analysis (CBC and clinical chemistry) or
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Vaughn et al. Cannabinoid Safety in Dogs
further processing. For the K2EDTA tubes intended for analysis
of CBD, THC, and their metabolites, plasma was separated into
two equal aliquots and stored at −80◦C until shipment on dry ice
to the bioanalytical laboratory for analysis (InterVivo Solutions,
Inc., Mississauga, ON).
CBD, THC, 7-COOH-CBD, and 11-OH-THC were analyzed
by liquid chromatography tandem mass spectrometry (LC-
MS/MS) (QTRAP R
6500 with an Exion LCTM system, AB
Sciex LP). The analytes CBD, THC and 11-OH-THC were
purchased as analytical reference solutions from Sigma-
Aldrich; 7-COOH-CBD was purchased from Toronto Research
Chemicals. The analytes were chromatographically separated
on a Phenomenex Kinetex Phenyl-Hexyl column (2.1 ×
50 mm, 2.6 µm) using gradient elution (mobile phase A
=0.1% formic acid in water and mobile phase B =0.1%
formic acid in acetonitrile) at a flow rate of 0.4 mL/min.
The mass spectrometer was operated in multiple reaction
monitoring (MRM) mode with a turbo ion spray interface.
Internal standards were deuterated analogs of THC, CBD, and
11-OH-THC (THC-d3, CBD-d3, 11-OH-THC-d3, Toronto
Research Chemicals); paclitaxel was used as the internal standard
for 7-COOH-CBD. All four compounds were analyzed in
one run.
Calibration standards were prepared in blank pooled dog
plasma (with K2EDTA as anticoagulant). Ten calibration
standards over the range of 0.25–2,000 ng/mL (CBD,
THC) or 0.5–2,000 ng/mL (7-COOH-CBD, 11-OH-THC)
were used and included a blank sample (without internal
standard) and a zero sample (with internal standard). Plasma
standards and samples were extracted by the addition of
a solution of 50/50 methanol/acetonitrile containing the
internal standards to precipitate the proteins. A sample batch
consisted of the following: 3 replicates of a system suitability
standard (containing the analyte and internal standard),
calibration standards in ascending order including a blank
sample (without internal standard), a zero sample (with
internal standard), and 10 non-zero standards, the assay
samples, followed by the 3 replicates of the system suitability
sample. Calibration standards bracketed an analysis batch of
>40 samples.
Acceptance criteria for method qualification and sample
analysis were: (1) that at least 75% of the non-zero calibration
standards be included in the calibration curve with all back-
calculated concentrations within ±20% deviation from nominal
concentrations (except for the lower level of quantification,
LLOQ, where ±25% deviation was acceptable), (2) the
correlation coefficient (r) of the calibration curve must be
≥0.99, and (3) the area ratio variation between the pre-
and post-run injections of the system suitability samples is
within ±25%.
Data Analysis
Measures of central tendency (mean), variability (standard
deviation, standard error of mean), and all figures were generated
by GraphPad Prism version 8.1.2 for Windows, GraphPad
Software, San Diego, California, USA, www.graphpad.com.
RESULTS
Four of 24 dogs evaluated for inclusion into the study were
excluded from study enrollment following the acclimation period
due to recurring loose stool (n=1), recurring ear infections
(n=1), and inadequate maintenance of body weight (n=2).
Therefore, 20 dogs were randomized to treatment groups (with
4 dogs per group). The mean (SD) body weights of each group
at baseline were as follows: MCT oil: 12.2 kg (1.1 kg); CBD oil:
10.3 kg (0.4 kg); THC oil: 12.3 kg (1.0 kg); SF oil: 11.9 kg (1.5 kg);
CBD/THC oil: 11.3 kg (0.9 kg).
Of the cannabinoid oils tested, dosing of the CBD oil had the
least effect on food intake and physical activity. Specifically, food
intake decreased on dosing days as compared to non-dosing days
by 4.6% (MCT oil), 8.1% (CBD oil), 27.9% (THC oil), and 44.7%
(CBD/THC oil), with no changes observed between these periods
with SF oil (data not shown). Dogs were not exercised/socialized
on dosing days and physical activity (measured by Actiwatch-
64 R
) was thus reduced across all groups on dosing days as
compared to non-dosing days by 12.9% (MCT oil), 19.2% (CBD
oil), 19.8% (THC oil), 24.4% (SF oil), and 40.7% (CBD/THC oil)
(data not shown). Despite these changes, body weights remained
stable throughout the study period across the five groups.
Dose Escalation and Subject
Discontinuation
The two placebo oils were tested up to 10 escalating volumes
while the CBD oil, THC oil, and CBD/THC oil were tested
up to the tenth, tenth, and fifth dose, respectively; titration to
maximum doses of 640.5 mg CBD (∼62 mg/kg), 597.6 mg THC
(∼49 mg/kg), and 140.8/96.6 mg CBD/THC (∼12 mg/kg CBD +
8 mg/kg THC), respectively, was thus achieved (Tables 1,2). For
the cannabinoid oils, the second cannabinoid dose was 2- to 2.5-
fold greater than the first dose; thereafter, serial doses increased
by 1.2- to 2-fold.
One of four dogs in the THC oil group experienced severe
ataxia at the 7th dose and was discontinued from further dosing.
Two of four dogs in the CBD/THC oil group experienced severe
ataxia and/or lethargy at the fourth or fifth doses (one dog at
the fourth dose and a second dog at the fifth dose) and thus
further dosing ceased for all dogs in this group. No dogs were
discontinued from the CBD oil or placebo oil groups as a result
of AEs.
Adverse Events
AEs were reported in all 20 dogs across the five groups. Of the
total number of AEs observed across the entire study (n=505),
104 AEs occurred in the placebo groups across 10 escalating
volumes (77 AEs with MCT oil and 27 AEs with SF oil), and 401
AEs occurred across the three cannabinoid groups: 80 AEs with
CBD oil (10 doses), 206 AEs with THC oil (10 doses), and 115
AEs with CBD/THC oil (five doses) (Figure 1). The SF oil group
was the placebo control for the CBD/THC oil group, the latter
which was delivered up to five doses; as such, while there were 27
AEs across 10 doses of SF oil, there were 11 AEs across the first
five doses of SF oil (Figure 1).
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Vaughn et al. Cannabinoid Safety in Dogs
FIGURE 1 | Total number and severity (mild, moderate, severe) of AEs experienced across five escalating doses of SF oil placebo (n=4) and CBD/THC oil (n=3 or
4) and 10 escalating doses of MCT oil placebo (n=4), CBD oil (n=4), and THC oil (n=3 or 4). There were no moderate or severe AEs experienced with CBD oil and
SF oil.
Across the three groups receiving cannabinoid oils, the
fewest AEs were reported in the CBD oil group (across 10
doses) as compared to the THC oil group (across 10 doses)
and the CBD/THC oil group (across five doses) (Figure 1).
Compared to dogs receiving the CBD oil, dogs receiving the
THC oil experienced 2.6-fold more total AEs (Figure 1) and,
more specifically, 7-fold more neurological and constitutional
AEs, 5-fold more dermatological AEs, and 3-fold more ocular
and respiratory AEs (Figure 2). The greatest difference between
the CBD oil and THC oil groups with respect to the occurrence
of AEs occurred at the first dose at which point there was a 7-
fold difference in the average number of AEs experienced per
dog (Figure 3). For the remaining nine doses, dogs receiving the
THC oil experienced between a 2- and 3-fold greater number of
AEs per dose vs. dogs receiving the CBD oil (Figure 3). With
respect to the CBD/THC oil group, there was a steep increase
in the average number of AEs per dog at the fifth dose; each
of the three dogs experienced 10 AEs at this dose vs. the other
two cannabinoid oil groups wherein an average of 4.8 AEs (THC
oil group) and 1.5 AEs (CBD oil group) were experienced per
dog (Figure 3). It is noteworthy that the total number of AEs
and the AE profile in the CBD oil group were comparable to
the MCT placebo oil group (Figures 1,2). Moreover, across the
cannabinoid oil groups, at each escalating dose, dogs in the
CBD oil group experienced a lower average number of AEs as
compared to the THC oil group and the CBD/THC oil group
(Figure 3).
The majority of AEs in each of the five groups, and collectively
across all five groups, were mild. Mild AEs accounted for 479 of
the 505 total study AEs (94.9%) (Figure 1). Mild AEs occurred
in all subjects and mainly manifested as gastrointestinal (nausea,
emesis, diarrhea), constitutional (lethargy, hyperesthesia), or
neurological (muscle tremor, ataxia) symptoms (Figure 2). The
proportion of mild AEs that were gastrointestinal in each group
was: 49/75 (65.3%) (MCT oil; 10 doses), 53/80 (66.3%) (CBD oil;
10 doses), 64/203 (31.5%) (THC oil; 10 doses), 9/11 (81.8%) (SF
oil; five doses), 16/94 (17.0%) (CBD/THC oil; five doses). The
proportion of mild AEs that were constitutional or neurological
in each group was: 13/75 (17.3%) (MCT oil; 10 doses), 13/80
(16.3%) (CBD oil; 10 doses), 89/203 (43.8%) (THC oil; 10 doses),
0/11 (SF oil; five doses), 56/94 (59.6%) (CBD/THC oil; five
doses). Thus, across the two placebo groups (SF oil, MCT oil)
and the CBD oil group, a greater proportion of mild AEs were
gastrointestinal vs. constitutional/neurological whereas in the
THC oil and CBD/THC oil groups, a greater proportion of mild
AEs were constitutional/neurological vs. gastrointestinal.
There were no moderate AEs in the CBD oil group at any
of the doses tested. Moderate AEs accounted for 22 of the 505
total study AEs (4.4%) and occurred in 40% of the subjects
(8 of 20 dogs) across three groups: MCT oil (two dogs at
the tenth dose), THC oil (two dogs at the third or seventh
doses), or CBD/THC oil (four dogs across the five doses tested)
(Figure 1). Moderate AEs manifested as constitutional (lethargy,
hypothermia) or neurological (ataxia) symptoms. The most
common moderate AE was hypothermia (rectal temperature
<36.0◦C), which accounted for 14 of the 22 moderate AEs (64%).
The majority of hypothermia occurrences (13 of 14) occurred
in the CBD/THC oil group, wherein all 4 dogs experienced
hypothermia at four of the five doses tested (excluding the first
dose). The lowest dose of CBD/THC oil at which hypothermia
occurred was at the second dose (35.2/24.2 mg CBD/THC = ∼3
mg/kg CBD and ∼2 mg/kg THC). The remaining hypothermia
event occurred in the THC oil group at the third dose (82.2 mg
THC = ∼7 mg/kg THC). Indeed, as compared to the other
cannabinoid and placebo oils, a greater decline in the rectal
temperature of dogs occurred following intake of the CBD/THC
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Vaughn et al. Cannabinoid Safety in Dogs
FIGURE 2 | Total number of mild AEs per anatomic category. Mild AEs
accounted for the majority (94.9%) of AEs. (A) Mild AEs across 10 doses of
MCT oil placebo (n=4), CBD oil (n=4), or THC oil (n=3 or 4). (B) Mild AEs
across five doses of SF oil placebo (n=4) or CBD/THC oil (n=3 or 4).
Gastrointestinal =nausea, vomiting, diarrhea, or other (hematemesis or blood
or mucus in stool); Constitutional =lethargy, hyperesthesia, hypothermia, or
other (weight loss, hypertonia, eyebrows raised and no blinking, abnormal
posture, vocalization); Neurological =tremor (including hiccups) or ataxia;
(Continued)
FIGURE 2 | Ocular =mydriasis or other (epiphora, conjunctivitis,
blepharospasm); Dermatological =pruritus or other (skin ulceration, purpura,
alopecia, erythema, granuloma); Respiratory =nasal discharge or
bradypnoea; Cardiovascular =bradycardia; Otic =external ear inflammation;
Genitourinary =urinary incontinence or hematuria.
oil (Figure 4). Moderate AEs were transient and resolved in
3–24 h. Importantly, there were no moderate AEs, including
hypothermia, in the CBD oil group at any of the doses tested.
There were no severe/medically significant AEs in the CBD
oil group at any of the doses tested. Severe AEs accounted for
4 of the 505 total study AEs (0.8%) (Figure 1) and occurred
in 15% of the subjects (3 of 20 dogs) across two groups:
THC oil (one dog at the seventh dose) and CBD/THC oil
(one dog at the fourth dose and a second dog at the fifth
dose). Severe AEs manifested as severe ataxia and/or lethargy
and were transient, resolving in 9–28 h. Plasma levels of CBD,
THC, and their metabolites measured upon observation of
severe AEs were 785 ng/mL THC and 93.9 ng/mL 11-OH-
THC (THC oil group) and 133–296 ng/mL CBD and 99.5–
361 ng/mL THC (CBD/THC oil group). Bloodwork results
from animals experiencing severe AEs revealed abnormalities
(low platelet count, high pancreatic sensitive lipase, high white
blood cell count, high neutrophils, and/or high monocytes)
only in the two dogs administered the CBD/THC oil; these
abnormalities resolved within 24 h. There were no abnormal
physical findings of the dogs on final examinations conducted by
the facility’s veterinarian.
Hematological Changes
Clinical Chemistry and Complete Blood Count
For the cannabinoid oil groups, blood was collected at baseline,
and 24 h and 7 days after the final dose. Overall, hematological
parameters were generally normal for the dogs across these
groups at 24 h and 7 days after the final dose, with a few
exceptions as outlined below.
With respect to changes in clinical chemistry parameters
suggestive of altered liver function, while possibly not clinically
pathologic, we interpreted a notable change to be: (i) at least
a 2-fold increase from baseline to post final dose timepoints
(24 h or 7 days) in total bilirubin or plasma levels of liver
enzymes [alkaline phosphatase (ALP), alanine aminotransferase
(ALT), aspartate aminotransferase (AST), gamma-glutamyl
transpeptidase (GGTP)]; and (ii) the post final dose level (24 h
or 7 days) in the above parameters reached or exceeded the upper
limit of normal. Applying these criteria, one dog in the CBD oil
group and one dog in the CBD/THC oil group experienced 2.9-
fold or 3.6-fold increases in ALP from baseline to 24 h following
the last administered dose, which was the tenth dose (CBD oil) or
the fifth dose (CBD/THC oil), respectively (Table 4). Moreover,
the post final dose level (at 24 h) approached or exceeded the
upper cut-off of normal for ALP. Comparing the 7 days post
final dose ALP levels for these two dogs to the 24-h post final
dose levels showed a downward trend (Table 4). Plasma levels
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Vaughn et al. Cannabinoid Safety in Dogs
FIGURE 3 | Average number (SEM) of AEs per dog per administered dose of oil. (A) Ten doses of MCT oil placebo (n=4), CBD oil (n=4), or THC oil (n=3 or 4)
were administered. (B) Ten doses of SF oil placebo (n=4) and five doses of CBD/THC oil (n=3 or 4) were administered.
FIGURE 4 | Rectal temperature (mean ±SEM) after the 4th dose of the cannabinoid oils or the 6th dose of the placebo oils, measured on the same calendar day. (A)
MCT oil (n=4) vs. CBD oil (n=4; 137.3 mg CBD) vs. THC oil (n=4; 109.6 mg THC). (B) SF oil (n=4) vs. CBD/THC oil (n=4; 105.6/72.5 mg CBD/THC). Rectal
temperature was measured pre-dose (time 0) and 1, 2, 3, 4, 6, and 9h post-dose. The dotted line corresponds to a rectal temperature of 36.0◦C, below which the
dogs were considered to have hypothermia.
of liver enzymes and total bilirubin were stable in the THC
oil group.
With respect to the remaining CBC and clinical chemistry
parameters, blood collected 24 h following the final dose of the
cannabinoid oils showed only a few abnormalities as based on
laboratory reference ranges. These abnormalities occurred in 1 or
2 dogs in the cannabinoid oil groups and consisted of low creatine
phosphokinase (1 dog in CBD oil group); low amylase, high
sodium, or high pancreatic sensitive lipase (2 dogs in THC oil
group); high pancreatic sensitive lipase (1 dog in the CBD/THC
oil group) (data not shown). All abnormalities resolved 7 days
following the final dose.
Cannabinoids and Their Metabolites
Following intake of the ninth dose of the CBD oil (n=4) or THC
oil (n=3), plasma levels of CBD, THC, and their metabolites
(7-COOH-CBD, 11-OH-THC) were measured 1, 2, 4, 6, and
24 h post-dose; levels of these parameters were also measured
pre-dose (Figure 5).
Intake of the ninth dose of the CBD oil (549.0 mg CBD;
∼53 mg/kg) led to steady inclines in plasma CBD, 7-COOH-
CBD and THC over the 6-h post-dose period (Figure 5). Levels
(mean/SEM) of CBD and THC at 6 h post-dose were similar to
levels 24 h post-dose [CBD: 334.0 ±193.0 ng/mL (6 h) and 347.0
±204.5 ng/mL (24 h); THC: 10.5 ±6.3 ng/mL (6 h) and 9.8 ±
6.5 ng/mL (24 h)]. In contrast, levels of 7-COOH-CBD were 2-
fold lower at 6 vs. 24 h post-dose (39.1 ±23.0 ng/mL and 82.8 ±
38.4 ng/mL, respectively).
Following intake of the ninth dose of the THC oil (448.2 mg
THC; ∼37 mg/kg), mean (SEM) plasma THC and 11-OH-
THC reached maximum levels of 69.8 ±28.8 ng/mL (THC, 1 h
post-dose) and 5.9 ±2.7 ng/mL (11-OH-THC, 2 h post-dose),
respectively, with steady declines observed thereafter over the
6-h post-dose period. Mean plasma THC at 6 h post-dose (21.1
±5.1 ng/mL) was similar to its level 24 h post-dose (18.2 ±
7.6 ng/mL). Mean plasma 11-OH-THC at 6 h post-dose (3.7
±1.8 ng/mL) was similar to its level 24 h post-dose (4.5 ±
1.7 ng/mL).
Across the cannabinoid oil groups, cannabinoids and their
metabolites were measured 7 days following the last administered
dose. Seven days following intake of the last (tenth) dose of the
CBD oil (640.5 mg CBD; ∼62 mg/kg; n=4), CBD was detected
in all four dogs (3.6–31.7 ng/mL) while levels of 7-COOH-CBD
were detected in half the dogs (1.4–1.8 ng/mL) (data not shown).
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Vaughn et al. Cannabinoid Safety in Dogs
TABLE 4 | Clinical chemistry plasma parameters indicative of liver function as measured in healthy Beagle dogs administered cannabinoid oils.
AST (U/L) ALT (U/L) ALP (U/L) GGTP (U/L) Total Bilirubin (µmol/L)
RR =15–66 U/L RR =12–118 U/L RR =5–131 U/L RR =1–12 U/L RR =0.0–5.1 µmol/L
BSN 24 h post FD 7 d post FD BSN 24 h post FD 7 d post FD BSN 24 h post FD 7 d post FD BSN 24 h post FD 7 d post FD BSN 24 h post FD 7 d post FD
CBD OIL
Dog 1 23 21 21 21 21 20 44 127a93 3 3 4 2.4 1.6 1.3
Dog 2 24 23 23 23 25 24 80 94 123 3 3 3 3.2 2.2 2.3
Dog 3 21 17 18 29 28 29 43 69 66 6 4 4 2.3 1.7 1.7
Dog 4 25 23 22 24 45 31 48 83 80 4 6 4 2.2 1.1 1.5
Mean (SD) 23.3 (1.7) 21.0 (2.8) 21.0 (2.2) 24.3 (3.4) 29.8 (10.6) 26.0 (5.0) 53.8 (17.6) 93.3 (24.7) 90.5 (24.3) 4.0 (1.4) 4.0 (1.4) 3.8 (0.5) 2.5 (0.5) 1.7 (0.5) 1.7 (0.4)
THC OIL
Dog 1 16 15 13 19 22 20 40 46 49 5 3 3 1.8 1.6 1.4
Dog 2b23 21 19 21 24 20 26 37 27 4 1 5 2.6 2.1 1.8
Dog 3 16 23 18 19 21 23 21 27 29 2 4 4 2.8 2.0 1.7
Dog 4 26 19 20 22 24 23 35 33 39 4 4 2 2.2 1.8 1.8
Mean (SD) 20.3 (5.1) 19.0 (4.0) 17.0 (3.6) 20.3 (1.5) 22.3 (1.5) 22.0 (1.7) 30.5 (8.6) 35.3 (9.7) 39.0 (10.0) 3.8 (1.3) 3.7 (0.6) 3.0 (1.0) 2.4 (0.4) 1.8 (0.2) 1.6 (0.2)
CBD/THC OIL
Dog 1 27 18 19 40 42 41 52 189c88 3 3 4 2.5 1.7 2.0
Dog 2d24 21 24 30 32 34 60 96 79 3 3 4 2.0 2.6 1.7
Dog 3 26 24 19 28 24 39 36 55 42 2 3 1 3.7 1.9 2.3
Dog 4 21 19 16 21 66 29 25 41 37 3 5 5 2.6 2.3 2.1
Mean (SD) 24.5 (2.6) 20.3 (3.2) 18.0 (1.7) 29.8 (7.8) 44.0 (21.1) 36.3 (6.4) 43.3 (15.7) 95.0 (81.7) 55.7 (28.1) 2.8 (0.5) 3.7 (1.2) 3.3 (2.1) 2.7 (0.7) 2.0 (0.3) 2.1 (0.2)
ALP, alkaline phosphatase; ALT, alanine aminotransferase; AST, aspartate aminotransferase; BSN, baseline; CBD, cannabidiol; d, days; FD, final dose; GGTP, gamma-glutamyl transpeptidase; h, hours; RR, reference range; SD, standard
deviation; THC, delta-9-tetrahydrocannabinol; U/L, units per liter.
aALP level 2.9-fold higher than baseline and approaching the upper limit of normal (131 U/L).
bThe 7th dose was the last dose due to a severe/medically significant AE with this dose. Calculation of the mean (SD) for all post FD outcomes excluded this dog’s data.
cALP level 3.6-fold higher than baseline and exceeded the upper limit of normal (131 U/L).
dThe 4th dose was the last dose due to a severe/medically significant AE with this dose. Calculation of the mean (SD) for all post FD outcomes excluded this dog’s data. For the remaining dogs in this group, the 5th dose was the
last dose.
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Vaughn et al. Cannabinoid Safety in Dogs
FIGURE 5 | Plasma levels (mean ±SEM) of CBD, THC, and their metabolites (7-COOH-CBD, 11-OH-THC) pre-dose, and at 1, 2, 4, 6, and 24 h following the 9th dose
of (A) CBD oil (549.0mg CBD; n=4) or (B) THC oil (448.2mg THC; n=3). Following exposure to the CBD oil, levels of 11-OH-THC were not detected or were below
the lower level of quantitation in the majority of dogs. Following exposure to the THC oil, there were no detectable levels of CBD or its metabolite (7-COOH-CBD).
Seven days following intake of the last (tenth) dose of the THC
oil (597.6 mg THC; ∼49 mg/kg; n=3), THC was detected
in all three dogs (2.8–8.2 ng/mL), while 11-OH-THC was not
detected in any dogs (data not shown). Seven days following the
intake of the last (fifth) dose of the CBD/THC oil (140.8/96.6 mg
CBD/THC; ∼12 mg/kg CBD +8 mg/kg THC; n=3), CBD and
THC were detected in all three dogs (CBD: 8.4–18.8 ng/mL; THC:
6.2–12.2 ng/mL), while 7-COOH-CBD was detected in one of
three dogs (1.4 ng/mL) and 11-OH-THC was not detected in any
of the three dogs (data not shown).
DISCUSSION
In our study, a CBD-predominant oil consumed via 10 escalating
doses containing 18.3–640.5 mg CBD per dose (∼2–62 mg/kg)
led to only mild AEs and no moderate or severe AEs. Importantly,
the number and type of AEs that occurred in the CBD oil group
were comparable to the corresponding placebo group (MCT oil).
In both groups, the majority of AEs were gastrointestinal, which
could have been due to discomfort with oral gavage, oil volume,
and/or the MCT oil carrier.
The safety and tolerability of CBD, as determined primarily
in rodents and humans, has been extensively reviewed (6–8). In
humans, oral doses of CBD ranging from a minimum of 15 or 20
mg/day (24,25) to a maximum of 1,200–1,500 mg/day (26–28)
have been well-tolerated, with no significant side effects. In mice,
oral doses ranging from 3 to 100 mg/kg showed no significant
effects on catalepsy (29). In dogs, CBD has shown to be well-
tolerated at doses ranging from 2 to 2.5 mg/kg twice daily for
4 or 12 weeks (17,21) to 5 or 10 mg/kg twice daily for 6 weeks
(20). Indeed, in their critical review report on CBD, the World
Health Organization (WHO) concluded that “CBD is generally
well-tolerated with a good safety profile (. . . ) and relatively low
toxicity” (8).
Previous studies have reported increases in liver enzymes,
specifically ALP, in dogs receiving CBD orally at doses ranging
from 2 mg/kg (twice daily) to 10 mg/kg (twice daily) for
4, 6, or 12 weeks (17,20,21) with increases observed as
early as 2 weeks following treatment initiation (20). In our
study, one dog in the CBD oil group and one dog in the
CBD/THC oil group experienced 2.9- or 3.6-fold increases in
ALP from baseline to 24 h following the tenth dose (CBD
oil) or fifth dose (CBD/THC oil). These changes were not
considered clinically significant by the veterinarian providing
oversight for the study. Elevated liver enzymes with exposure
to cannabis or CBD have also been observed in humans and
rodents. Cross-sectional human studies have shown plasma ALP
to be elevated in habitual daily cannabis users (30,31) with
hepatomegaly also observed (31). Increases in plasma AST, ALT,
and liver-to-body weight ratios were observed in rodents treated
with CBD (oral gavage; 615 mg/kg for 10 days) albeit there
were unremarkable changes in liver enzymes in lower dose
groups (61.5 and 184.5 mg/kg) (32). The potential short- and
long-term effects of CBD on liver function in dogs warrant
further investigation.
Only in the CBD/THC oil group were severe AEs experienced
by more than one dog causing cessation of dosing after the
fifth dose. Researchers have acknowledged that CBD can have
interactions with THC (33) and that CBD is not always a
functional antagonist of THC (34). Indeed, there is evidence
in rodents (33–37) and humans (38) that CBD can potentiate,
rather than antagonize, the psychoactive and physiological effects
of THC (e.g., locomotor activity suppression, hypothermia,
hypoactivity). The interaction between these two exogeneous
phytocannabinoids may be pharmacokinetic (CBD modifies the
effect of THC through changes in absorption, distribution,
and/or elimination) or pharmacodynamic (CBD modifies the
effect of THC via additive, synergistic, or antagonistic effects).
The interaction depends on whether CBD is administered
prior to THC (pharmacokinetic interaction more likely) or
concurrently with THC (pharmacodynamic interaction more
likely) (7,34,39) and also on the dose ratio of the compounds (39,
40). Regarding the latter, when CBD/THC are simultaneously
co-administered at a mean (±standard deviation) dose ratio of
8.1 (±11.1), antagonistic effects of CBD on THC have been
observed (a pharmacodynamic interaction) whereas at a ratio of
1.8 (±1.4), CBD has been shown to potentiate the effects of THC
(a pharmacokinetic interaction) (39,41). Our CBD/THC oil had a
CBD/THC dose ratio of 1.5. It therefore follows that the effects of
THC may have been potentiated by CBD via a pharmacokinetic
interaction. CBD is known to be a potent inhibitor of hepatic
drug metabolism (39) by inactivating cytochrome P450 enzymes.
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Vaughn et al. Cannabinoid Safety in Dogs
When co-administered with THC, this effect can delay the
metabolism of THC in the liver (7,34). Notwithstanding that the
levels of other cannabinoids (THCA, CBDA, CBG, CBGA, CBN,
CBC) and terpenes in the CBD/THC oil fell below reporting
limits (0.5 mg/mL for cannabinoids and 0.01% for terpenes),
their potential interaction with CBD and/or THC in the oil
and their contribution to the overall effect of the CBD/THC
oil cannot be precluded (this synergy is often called the
“entourage effect”).
Our data show a clear distinction in AEs associated with a
CBD-predominant oil vs. oils containing higher levels of THC in
that constitutional (lethargy, hyperesthesia, hypothermia)
and neurological (tremor, ataxia) AEs most commonly
occurred in dogs receiving the THC oil or the CBD/THC
oil. Suppression of locomotor activity (hypolocomotion),
catalepsy, and hypothermia have been observed across species
(dogs, cats, rodents, chickens) and associated with exposure
to cannabis, THC, or THC and CBD in combination, but not
CBD alone (33,37,42–45). Animal studies have shown that
the production of these effects is dependent on cannabinoid
type 1 (CB1) receptor activation (45). CB1 receptors are located
primarily in central and peripheral neurons and are found
in the highest densities in the neuron terminals of the basal
ganglia, cerebellum, hippocampus neocortex, hypothalamus,
and limbic cortex—areas which, among other functions, are
involved in motor activity, coordination, and sedation (46,47).
THC, a CB1 receptor partial agonist, has a high affinity for
CB1 receptors (48) and is capable of binding and activating
them at orthosteric sites (45,49). In contrast, CBD does not
bind to orthosteric sites of these receptors like THC (49). In
our study, there was a lower proportion of constitutional and
neurological AEs following intake of CBD oil (vs. THC oil and
CBD/THC oil) and no moderate or severe AEs were experienced
by dogs in the CBD oil group. CBD’s lack of interaction with
orthosteric sites of CB1 receptors (49) is a plausible explanation
for the fewer and less severe AEs experienced by dogs receiving
CBD oil.
Plasma levels of CBD, THC, and their metabolites were
highly variable between dogs in the same treatment group
receiving either the ninth dose of CBD oil or THC oil. Others
have also observed high variability in cannabinoid (CBD, THC)
blood concentrations across dogs in single dose pharmacokinetic
studies (16,19) and repeated administration studies (21),
which may be explained by differences in absorption rates or
cannabinoid metabolism across subjects. Following the ninth
dose of the CBD oil (∼53 mg/kg), maximum plasma CBD levels
achieved across the four dogs in the CBD oil group (62.3–
896.0 ng/mL, at 4, 6, or 24 h post-dose) were comparable to the
range in plasma CBD levels achieved across nine dogs (∼130–
940 ng/mL) following repeated daily CBD dosing (2.5 mg/kg
twice daily) for 12 weeks (21). With respect to plasma levels
reached following the ninth dose of the THC oil (∼37 mg/kg),
at 24 h post-dose, mean plasma THC (18.2 ng/mL) and 11-
OH-THC (4.5 ng/mL) across three dogs approximated mean
plasma levels reached by eight dogs receiving a cannabis extract
(2.7 mg/kg THC +2.5 mg/kg CBD) for 56 weeks: 22.0 ng/mL
(THC) and 6.7 ng/mL (11-OH-THC) (11). Thus, it appears that
repeated daily dosing of lower cannabinoid doses can achieve
comparable plasma CBD or THC levels to acutely administered
higher doses.
Contrary to earlier assertions that CBD has low bioavailability
after oral administration to animals, including dogs (18,50),
our study showed circulating plasma CBD and 7-COOH-
CBD in all dogs receiving the ninth dose of CBD oil at all
post-dose timepoints (1, 2, 4, 6, and 24 h). Based on these
results, it appears that a first pass effect through the liver
did not eliminate the systemic availability of CBD following
its oral ingestion. Given the highly lipophilic nature of CBD
(50), its administration in a lipid solvent (MCT oil) in the
present study may have increased its bioavailability. Zgair
et al. (51) showed that co-administration of lipids with oral
CBD increased systematic availability of CBD by almost 3-
fold in rats as compared to lipid-free formulations. Overnight
fasting of the dogs in the present study prior to dosing may
have also improved bioavailability. Lebkowska-Wieruszewska
et al. (19) showed improved cannabinoid (THC) bioavailability
in fasted vs. fed dogs, with a lower Tmax and higher Cmax
achieved for THC in the fasted condition. The approximate
cumulative CBD dose administration from the first to ninth
dose was 2122.9 mg. Detected plasma levels of CBD may also be
reflective of CBD accumulation in plasma with dose escalation
over time.
Fasted dogs receiving the ninth dose of the THC oil
(cumulative THC from first to ninth dose =1653.5 mg) achieved
maximum THC plasma levels at 1-h post-dose. Related findings
are those reported by Lebkowska-Wieruszewska et al. (19) who
calculated median Tmax levels for plasma THC of 1.25 h in
fasted dogs orally dosed with Bedrocan R
(1.5 mg THC/kg). It
is reported in the literature that following oral ingestion of
cannabis, maximum plasma THC levels are reached within 1–
2 h (52). Decreases in plasma THC observed in our study after
1 h are suggestive of the uptake of THC by fat tissues and highly
vascularized tissues, such as the brain and muscle (52). Indeed,
in the THC oil group, the average onset of neurological AEs
(ataxia, tremor) or constitutional AEs (lethargy, hyperesthesia,
hypothermia, hypertonia) was ∼4 h post-dose (range of onset was
1–24 h).
Both CBD and THC were detected in plasma 1 week following
administration of the final dose of either CBD oil (∼62 mg/kg;
n=4) or THC oil (∼49 mg/kg; n=3), at levels ranging from
3.6 to 31.7 ng/mL CBD (CBD oil) and 2.8 to 4.6 ng/mL THC
(THC oil). This finding is relevant to future studies which apply a
crossover design and include a washout period. That quantifiable
levels of CBD were observed one week following dose exposure
is also interesting given that CBD has been reported to have a
relatively rapid elimination in dogs [CBD has been shown to be
bio-transformed in dogs via hydroxylation, carboxylation, and
conjugation (10,18)].
The cannabinoid oils used in this study are proprietary
formulations with relatively high concentrations of CBD
and/or THC and low concentrations of other cannabinoids
and terpenes. Given the multitude of factors that can affect
the proportion of constituents in the cannabis plant (light,
temperature, humidity, soil type during cultivation, plant
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Vaughn et al. Cannabinoid Safety in Dogs
genetics) and a final formulation (extraction procedures used),
our findings are most relevant to our investigated oil-
based formulations and may not be applicable to the safety
of other marketed formulations consisting of a different
profile of cannabinoids and other cannabis constituents (e.g.,
terpenes) and delivered in a different matrix (e.g., not
in an oil formulation). Our study was also a preliminary
safety study and, as such, a small number of animals were
used, which is a limitation. Additional larger studies that
investigate the safety of longer-term cannabinoid dosing in dogs
are needed.
Overall, our study provides novel data that separates
the relative safety and tolerability of dose escalation of
oil formulations predominant in plant-derived CBD,
THC, or CBD and THC in combination (1.5:1) in dogs.
Of the three cannabinoid oil formulations tested, dose
escalation of the CBD-predominant oil formulation was
the most tolerated by dogs up to a maximum dose of
640.5 mg CBD (∼62 mg CBD/kg) and only mild AEs were
experienced. Novel data on the in vivo metabolism of
CBD vs. THC when delivered at higher dose levels were
generated, which showed that CBD is absorbed more slowly
than THC.
Research on the potential health benefits of CBD in dogs
is beginning to emerge. Existing studies show its potential
as a single therapy for pain reduction in osteoarthritic
dogs (17) or as an adjunct therapy for the reduction in
seizure frequency in dogs with idiopathic epilepsy (21).
Our findings provide support for continuing research
on CBD’s safety profile and potential therapeutic uses in
dogs so that it may be considered a treatment option in
veterinary medicine.
DATA AVAILABILITY STATEMENT
The datasets generated for this study are not publicly available
to allow for commercialization of research findings. Reasonable
requests to access the datasets should be directed to Phil
Shaer (phil.shaer@canopygrowth.com).
ETHICS STATEMENT
All animal care and experimental procedures were conducted
under protocols approved by the facility’s Institutional Animal
Care and Use Committee (IACUC) and in accordance with the
Principles of the Animals for Research Act (53) and guidelines of
the Canadian Council on Animal Care (CCAC).
AUTHOR CONTRIBUTIONS
DV and JK were responsible for conception of the study, data
analysis, and provided intellectual input on the manuscript. LP
was responsible for data analysis and interpretation and writing
of the manuscript.
FUNDING
Canopy Animal Health, a division of Canopy Growth
Corporation, financially supported this research. There were no
conditions attached to the allocation of funds for this study.
ACKNOWLEDGMENTS
The authors would like to thank Martha Winhall, DVM
(InterVivo Solutions) for her review and feedback on the
manuscript and Graham Eglit for his input on data analysis.
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Conflict of Interest: DV, JK, and LP are employed by Canopy Animal Health,
which is a division of Canopy Growth Corporation. Staff at VivoCore Inc., and
not the authors, were responsible for study conduct and data collection.
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