Maca (L. meyenii) for improving sexual function: A systematic review

Abstract

Maca (Lepidium meyenii) is an Andean plant of the brassica (mustard) family. Preparations from maca root have been reported to improve sexual function. The aim of this review was to assess the clinical evidence for or against the effectiveness of the maca plant as a treatment for sexual dysfunction.
We searched 17 databases from their inception to April 2010 and included all randomised clinical trials (RCTs) of any type of maca compared to a placebo for the treatment of healthy people or human patients with sexual dysfunction. The risk of bias for each study was assessed using Cochrane criteria, and statistical pooling of data was performed where possible. The selection of studies, data extraction, and validations were performed independently by two authors. Discrepancies were resolved through discussion by the two authors.
Four RCTs met all the inclusion criteria. Two RCTs suggested a significant positive effect of maca on sexual dysfunction or sexual desire in healthy menopausal women or healthy adult men, respectively, while the other RCT failed to show any effects in healthy cyclists. The further RCT assessed the effects of maca in patients with erectile dysfunction using the International Index of Erectile Dysfunction-5 and showed significant effects.
The results of our systematic review provide limited evidence for the effectiveness of maca in improving sexual function. However, the total number of trials, the total sample size, and the average methodological quality of the primary studies were too limited to draw firm conclusions. More rigorous studies are warranted.

Full text

RESEARC H ARTIC LE Open Access
Maca (L. meyenii) for improving sexual function:
a systematic review
Byung-Cheul Shin
1
, Myeong Soo Lee
2,4*
, Eun Jin Yang
2
, Hyun-Suk Lim
3
, Edzard Ernst
4
Abstract
Background: Maca (Lepidium meyenii) is an Andean plant of the brassica (mustard) family. Preparations from maca
root have been reported to improve sexual function. The aim of this review was to assess the clinical evidence for
or against the effectiveness of the maca plant as a treatment for sexual dysfunction.
Methods: We searched 17 databases from their inception to April 2010 and included all randomised clinical trials
(RCTs) of any type of maca compared to a placebo for the treatment of healthy people or human patients with
sexual dysfunction. The risk of bias for each study was assessed using Cochrane criteria, and statistical pooling of
data was performed where possible. The selection of studies, data extraction, and validations were performed
independently by two authors. Discrepancies were resolved through discussion by the two authors.
Results: Four RCTs met all the inclusion criteria. Two RCTs suggested a significant positive effect of maca on sexual
dysfunction or sexual desire in healthy menopausal women or healthy adult men, respectively, while the other RCT
failed to show any effects in healthy cyclists. The further RCT assessed the effects of maca in patients with erectile
dysfunction using the International Index of Erectile Dysfunction-5 and showed significant effects.
Conclusion: The resul ts of our systematic review provide limited evidence for the effectiveness of maca in
improving sexual function. However, the total number of trials, the total sample size, and the average
methodological quality of the primary studies were too limited to draw firm conclusions. More rigorous studies are
warranted.
Background
Sexual problems (or sexual dysfunction) are widespread
and adversely affect mood, well-being, and interpersonal
relationships [1] . They occur in 20%-30% of men a nd
40-45% of women according to 18 descriptive epidemio-
logical studies from around the world [2]. Most sexual
problems relate to sexual desire (interest in sex) in both
females and males and male erectile dysfunction (ED) [2].
Current pharmacological interventions for the manage-
ment of sexual problems include oral drugs, intrapenile
therapies (intra-urethral suppositories and intracavernous
injections) and penile prosthesis implantation for males
and hormonal therapy for females. Although considerable
advances have been made, the ideal treatment for ED
has not been identified. The treatment for sexual pro-
blems in females is also problematic [3]. Furthermore,
pharmacological treatments have been shown to result in
several adverse effects, including risk of cancer, headache,
rhinitis and dyspepsia [4-6]. Non-phar macological treat-
ments of female sexual problems includes vaginal electro-
myography biofeedback, pelvic floor physical therapy,
(group) cognitive behaviouraltherapy,transcutaneous
electrical nerve stimulation, and vestibulectomy [7]. Her-
bal therapies for ED or sexual dysfunction in males and
females include yohimbine ( Pausinvstalia vohimbe),
which is burdened with s erious adve rse effe cts [8-10],
ginkgo (Ginkgo biloba) and red ginseng (Panax ginseng)
[10,11]. Sever al other botanical therapies for sexual dys-
function have also been introduced [8,10,12]. These are
also often used for improving sexual function in healthy
subjects.
Maca (Lepidium meyenii) is an Andean plant that
belongs to the brassica (mustard) family. Maca has been
used for centuries in the Andes to enhance fertility i n
humans and anim als [12,13] . Prepa rations from the
maca root have been reported to improve sexual
* Correspondence: drmslee@gmail.com
2
Division of Standard Research, Korea Institute of Oriental Medicine, Daejeon,
South Korea
Full list of author information is available at the end of the article
Shin et al. BMC Complementary and Alternative Medicine 2010, 10:44
http://www.biomedcentral.com/1472-6882/10/44
© 2010 Shin et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the t erms of the Creative Commons
Attribution License (http://crea tivecommons .org/licenses/b y/2.0), which permits unrestr icted u se, distribution, and reproduction in
any medium, provided the original work is properl y cited.

function in healthy populations [13]. Although maca is a
plant extract and not a drug, it is one of the most com-
monly cited “ natural drugs” on the Internet for the
improvement of sexual desire. The hypothesis that maca
may be effective in improving sexual function is sup-
ported by several lines of evidence. Animal experiments
suggest that maca has spermatogenic and fertility-
enhancing activities, which are likely due to the p hyto s-
terols or phytoestrogens present in the maca [14].
Several in vivo studies have shown that maca may
improve sexual behaviour and enhance androgen-like
effects in rats [15,16]. Recent clinical trials have also
suggested significant effects of maca for increasing
sperm count and m obility and im proving sexual func-
tion in humans [17,18]. The potential bioactive ingredi-
ents i n maca include macaridine, macamides, macaene,
gluosinolates, maca alkaloid, a nd maca nutrients [14].
However, these data are insufficient for determining
whether maca is clinically effective. Currently, no sys-
tematic review of this s ubject is available. The aims o f
this systematic review are to summarise and critically
assess the evidence from randomised clinical trials
(RCTs) for or against the effectiveness of maca in the
improvement of sexual fu nction, including sexual desire
and sexual responses.
Methods
Data sources
The following el ectronic databases were searched from
inception through April 2010: Medline, AMED, CINAHL,
EMBASE, PsycInfo, the Cochrane Central Register of
Controlled Trials and the Cochrane Database of Systema-
tic Review, DARE, Psychology and Behavioral Scienc es
Collection, six Korean Medical Databases (Korean Studies
Information, DBPIA, Korea Institute of Science and
Technology Information, KERIS, KoreaMed, and Korean
National Assembly Library), Chinese Medical Databases
(CNKI; http://www.cnki.net), and The Japanese Science
and Technology Information Aggregator, Electronic. The
search terms used were “Lepidium meyenii” AND sexual
dysfunction OR erectile dysfunction OR sexual function).
The search strategy was compose d of a mixture of f ree
text and thesaurus terms [see Additional file 1]. We also
manually searched our departmental files and relevant
journals (Focus on Alternative and Complementary
Therapies and Forschende Komplementärmedizin und
Klassische Naturheilkunde) until April 2010. The refer-
ences in all located articles were manually searche d for
further relevant articles. Dissertations and abstracts were
included.
Study selection
Trials involving pe ople with normal sexual function and
those with sexual dysf unction were incl uded. All articles
that reported an RCT in which humans were treated
with any type of maca (Lepidium meyenii) preparation,
regardless of origin, were included. Trials we re included
if they employed maca as the sole treatment or as an
adjunct to conventional treatments compared to a pla-
cebo control. Studies that used a t least one measure
related to sexual function were included. We excluded
trials comparing two different types o r dosages of maca
and t hose in which no clinical data or insufficient data
for comparison were reported. For duplicate publica-
tions with different outcome measures originating from
one trial published as separate papers, the original publi-
cation was given priority, and all others were excluded.
No language restrictions were imposed.
Extraction of data and assessment of risk of bias
All of the included articles were read in full. Three inde-
pendent reviewers (BCS, MSL, and EJY) extracted the
data, including methods (e.g., design, blinding, duration
of follow-up), sample (e.g., population size, conditions,
age, duration of disease), intervention and control treat-
ment, and outcome measures, according to predeter-
minedcriteria(Table1).TheCochraneclassification
(i.e., sequence gener ation, bl inding, incomplete outcome
measures, and allocation c oncealment) w as applied to
evaluate the risk of bias [19]. Differences in opinions
between the reviewers were settled through discussion.
Data Synthesis
We had originally intended to conduct a formal meta-
analysis. However, statistical an d clinical heterogeneity
prevented us from doing so. The main ways we would
have done were like followings. The post-treatment
values (the end of treatment) of the outcome measures
were used to assess differences between the intervention
groups and the control groups. We did not include the
follow-up treatment values. S tandardised mean differ-
ences (SMDs) were used for pooling the outcomes
related with sexual function with a random effects
model. SMDs and 95% confidence intervals (CIs) were
calculated using Cochrane Collaboration’ ssoftware
(Review Manager Version 5.0 for Windows, Copenha-
gen: The Nordic Cochrane Centre). The mean difference
(MD) for each outcome measure was calculated using
the same software. Statistical heterogeneity was evalu-
ated usi ng a c
2
test and I
2
statistics (low = 25 %; moder-
ate = 50%; high = 75%).
Results
Study description
The literature search es rev ealed 88 articles, of which 84
had to be excluded (Figure 1). Among these, one RCT
was excluded because it compared two different dosages
[20] and another because it reported different outcome
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measures from one trial [18]. One trial was excluded
because of the absence of a control group [17]. Four
RCTs met our inclusion criteria, and their key data are
summarised in Table 1 [21-24]. Of the fo ur studies, one
RCT was conducted in Italy [21], one in Peru [23], one
in Austra lia [22], and one in the UK [24]. One RCT
adopted a two-armed parallel group design [21], one
employed a three-armed parallel group design [23], and
the other two used a crossover design [22,24]. The four
trials included a total of 131 subjects. Two RCTs con-
tributed most to the sample ( n = 50, and 57) [21,23 ],
while the other tw o RCTs were relatively small (n = 8,
and 16) [22,24]. T wo RCT s [21 ,22] employed dried
maca, a nd the other two [23,24] used gelatinised maca.
All of the participants in the four studies ingested the
maca orally. Dosages were 1.5 g to 3.5 g of maca daily
for 2 or 12 we eks. The age ra nge of male participan ts
was from 21 to 56 years for healthy subjects and 36 ± 5
years for patients with ED, while the age range of post-
menopausal women was 54 ± 11 years. The outcome
measures used in these trials included the International
Index of Erectile Dysfunction (IIEF-5) [21], the sexual
dysfunction Green Climacteric Scale [22], sexual desire
according to the 6-point Likert scale [23], and the Sex-
ual Desire Inventory [24]. T hree RCTs [22-24] used
commercial products, and one RCT [21] tested natural
dried maca.
Risk of bias
None of the included RCTs reported their methods of
sequence generation. All of the included trials employed
a double-blind desi gn. One trial reported complete out-
come measures [22]. None employed allocation
concealment.
Table 1 Summary of randomised clinical trials with maca for sexual function
First
author
(year)
location
Sample size/
condition Age
(years) Sex (M/F)
Duration of disease
Intervention (regimen) Control
intervention
(regimen)
Main
outcome
measures
Results Adverse
effects
Zenico
(2009)
[21] Italy
50 mild ED
36 (SDs, 5)
(50/0)
n.r.
(A) Maca (pulverised dehydrated
maca roots directly imported from
Peruvian Andes, tablets, 2400 mg/d,
1200 mg/d, 2 daily for 12 weeks, n
= 25), no follow-up
(B) Placebo tablets
(2400 mg/d, 1200
mg/d, 2 daily for
12 weeks, n = 25)
IIEF-5 Intergroup: MD,
1.10 [0.61, 1.59],
P < 0.001
n.r.
Within group:
(A) P < 0.05,
(B) P < 0.05
Brooks
(2003)
[22]
Australia
16 healthy
postmenopausal
women with
moderate severity of
menopausal
symptoms
(A) Maca (company commercial
product, dried maca powder, 3500
mg/d, daily for 6 weeks, n = 14), 6
weeks follow-up
(B) Placebo
(refined white rice
flour, 3500 mg/d,
daily for 6 weeks,
n = 14)
Sexual
dysfunction
(GCS)
Intergroup: MD,
0.70 [0.08, 1.32], P < 0.05
n.r.
54 (SDs, 11)
(0/16)
>12 months
amenorrhea
Within group:
A) P < 0.05,
(B) NS
Gonzales
(2002)
[23] Peru
57 adult healthy men
21-56
(57/0)
N/A
(A) Maca (company commercial
product, gelatinised maca, 1500 mg/
d; 500 mg/d, 3 tablets, daily for 12
weeks, n = 30), no follow-up
(C) Placebo tablets
(n.r., daily for 12
weeks, n = 12)
Self-
perception
on sexual
desire
Intergroup: MD,
0.51 [-0.35, 1.37], NS at 4
weeks; MD, 1.64 [1.07, 2.21], P
< 0.008 at 8 weeks; MD, 1.64
[1.07, 2.21], P < 0.006 at 12
weeks
n.r.
(B) Maca (company commercial
product, gelatinised maca, 3000 mg/
d; 500 mg/d, 6 tablets, daily for 12
weeks, n = 15), no follow-up
Within group:
(A) P < 0.05 at 4, 8, and 12
weeks,
(B) NS at 4, 8, and 12 weeks
Stone
(2009)
[24] UK
8 experienced and
endurance trained
male (cyclists)
(A) Maca (company commercial
product, gelatinised maca, 2000 mg/
d for 2 weeks, n = 8), no follow-up
(B) Placebo
capsules (Arabic
gum, n = 8)
Sexual
Desire
Inventory
Intergroup: MD,
6.38 [-11.32, 24.08], NS
n.r.
30 (SDs, 7)
8/0
N/A
Cross-over (1 week
washout period)
Within group:
(A) P = 0.01,
(B) P = 0.90
ED: erectile dysfunction; GCS: Greene Climacteric Scale; IIEF-5: International Index of Erectile Dysfunction; NS: not significant; n.r.: not reported; SDs: standard
deviations
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Outcomes
Patients with sexual dysfunction
One RCT compared the effects of maca vs. placebo
treatments in patients with erectile dysfunction. This
trial [21] showed positive e ffects of maca on the IIEF-5
in patients with mild ED compared to the placebo con-
trol (MD, 1.10, 95% CIs, 0.61 to 1.59, P < 0.001) [21].
Healthy volunteers
Three RCTs tested the effects of maca vs. placebo on
sexual function in healthy postmenopausal women [22],
healthy adult men [23] o r male cyclists [24]. One RCT
[22] reported positive effects of maca on sexual function
in healthy menopausal women compared with the pla-
cebo control (MD, 0.70, 95% CIs, 0.08 to 1.32, P < 0.05).
The other RCT [23] tested both a high dosage of maca
(3 g/d) and a low dosage of maca (1.5 g/d) on sexual
desire compared to a placebo control and reported posi-
tive effects of both dosages of mac a after 8 weeks (MD,
1.64, 95% CIs, 1.07 to 2.21, P < 0.01) and 12 weeks
(MD, 1.64, 95% CIs, 1. 07 to 2.21, P < 0.01). The further
RCT [24], which had a very small sample size, failed to
show positive effects of maca in the improvement of
sexual desire (MD, 6.38, 95% CIs, -11.32 to 24.08, NS).
Adverse effects
None of included trials attempted to asse ss the adverse
effects of maca.
Discussion
Few RCTs have tested the effects of maca on sexual
function. This review found limited evidence from four
small trials that suggested that maca is effective in
Figure 1 Flow chart for the selection of included trials. RCT: randomised clinical trial; UOS: uncontrolled observational study.
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improving sexual des ire after at least 6 weeks. However,
this finding is limited because the studi es were un der-
powered. In particul ar, two studies found no effect after
2 or 4 weeks of treatment. Evidence from other studies
suggests that maca may be effective for sexual dysfunc-
tion in patients with ED and postmenopausal women
after 12 weeks or 6 weeks, respectively. However, the
total numb er of trials, the total sample size, and the
average risk of bias in the primary stud ies were too lim-
ited to draw firm conclusions.
All o f the RCTs employed double-blind methods, but
none of the included trials reported methods of
sequence generation for randomisation and allocation
concealment. Trials with inadequate sequence genera-
tion and inadequate allocation concealment are likely to
show exaggerated treatment effects [25] and thus limit
the reliability of the study results. Although all included
RCTs used placebo controls, none reported the success
of blinding. None of the studies reported a power calcu-
lation, and sample sizes were very small in some of the
RCTs (ranging from 8 to 57). One article h as a poor
description of the outcome and was therefore difficult to
interpret [23]. In this trial, only the mean average of two
active groups (high and low dosage of maca) was c om-
pared with the control group. One RCT failed to include
washout periods between cross over periods [22]. One of
the main problems in crossover trials is the possibility
of a carry-over effect. Therefore, this RCT is diff icult to
interpret. The other RCT has a smal l sample size and is
therefore susceptible to a type II error [24].
Four kinds of questionnaires were used for measuring
sexual function or sexual desire, including the IIEF-5
[21], Gre en Climacteric Scal e (GCS) [22], subjective
Likert scale [ 23], and Sexua l Desire Inv entory [24].
Three RCTs [21,22,24] employe d validated que stion-
naires , while one RCT [23] d id not. Because the GCS is
not specified for sexual function, it might not be sen si-
tive en ough to detect changes in sexual dysfunction.
One t rial tested changes in sexual desire compared to a
baseline value with a 6-point Likert scale. It is not clear
whether the authors used validated scales. It is impor-
tant that only valida ted questionnaires are employed;
otherwise, the outcome measures used have less estab-
lished reliability and validity, data derived from them are
subject to bias, and comparisons between the results of
different studies are problematic.
The extent to which the therapeutic effects of maca
dependonthetypeofmacausedandtheamountof
various constituents in the preparation is unclear. The
optimum dose of maca is unknown. Single-dose studies
used extract quan tities ranging from 1.5 g/d to 3.0 g/d.
One excluded RCT compared two dosages of maca, 1.5
g/d and 3.0 g/d, for the management of SSRI-induced
sexual dysfunction, but the results of that study failed to
show differences b etween the two doses [20]. Fu rther
studies are required to identify the optimal dose.
One argument for the use of maca for the management
of sexual function might be that it causes fewer adverse
effects than conventional drug treatments. However, none
of the four RCTs described here assessed the adverse
effects of maca. This should be tested in future studies.
One could question the validity o f our conclusions by
pointing to the review m ethod used (reviewing a small
number of trials with many limitat ions). However, the
reasons for doing a systematic review include answering
questions not addressed by individual studies, settling
controversies arising from apparently conflicting studies,
and generating new hypotheses [19].
The limitations of our systematic review pertain to the
paucity of da ta and the potential incompleteness of the
evidence reviewed. None of the three RCTs have been
submitted for independent replication. We aimed to
identify all studies on the topic. The distorting effects of
publication bias and location bias on systematic reviews
and meta-analyses are well documented [26]. None of
the RCTs included in our review were fully successful in
minimising bias. Co llectively, these facts seriously limit
the conclusiveness of our systematic review.
Our decision to exclude non-randomised trials might
also be criticised. However, we strongly feel that non-
randomisation introduces a selection bias that, in turn,
would render any results uninterpreptible. The exclusion
of RCTs comparing different dosages might be criticised.
We feel that such trials would not give objective clinical
information of value. Moreover, these studies cannot
provide reliable data on the effectiveness of maca.
Therefore, we believe the exclusion of such studies w as
the correct decision.
Regarding an implication for practice, this review
identifies limited evidencefortheuseofmacain
improving sexual function in healthy subjects or patients
with ED. However, practitioners and clinical decision
makers need to be aware that there are too many limita-
tions to draw firm conclusion. Future trials testing the
effects of maca should adhere to rigorous trial designs
that adequately suit the research question being asked.
Such trials should preferably be randomised , control for
placebo effects, be double-blinded, adequately conceal
allocation, have optimal treatment dosages and sample
sizes based on proper sample size calculations, use vali-
dated outco me measures, asse ss other outcomes such as
quality of life or partner outcome as well as adverse
effects, and include a full description of the actual inter-
ventions being tested.
Conclusion
The results of our systematic review provide limited evi-
dence for the effectiveness o f maca in the improvement
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of sexual function . However, the total number of trials,
the total s ample size, and the a verage methodological
quality of the primary studies were too limited to draw
firm conclusions. Moreo ver, our c urrent knowl edge of
the risks of maca intake is insufficient. More rigorous
studies are warranted.
Additional material
Additional file 1: The search strategies for MEDLINE. The data
provided the details of search strategies for MEDLINE.
Acknowledgements
Funding to pay the Open Access publication charge for this article was
provided by KIOM (K10251). M.S. Lee was supported by KIOM (K10251) and
E.J. Yang was supported by KIOM (K10010). ‘The fund for professional proof
reading of this article was supported by KIOM (K10010 and C10040).
Author details
1
Division of Clinical Medicine, School of Oriental Medicine, Pusan National
University, Yangsan, South Korea.
2
Division of Standard Research, Korea
Institute of Oriental Medicine, Daejeon, South Korea.
3
Department of
Nursing, Hanyang University Kuri Hospital, Kuri, Gyeonggi-Do, South Korea.
4
Complementary Medicine, Peninsula Medical School, University of Exeter,
Exeter, UK.
Authors’ contributions
BCS and MSL designed the review, performed searches, appraised and
selected trials, extracted data, contacted authors for additional data, carried
out analyses and interpretations of the data, and drafted this report. EJY
reviewed and critiqued this review and report and assisted with
interpretation of the data. HSL and EE reviewed and critiqued the review
protocol and this report and assisted in designing the review. All authors
read and approved the final manuscript.
Competing interests
The authors declare that they have no competing interests.
Received: 20 March 2010 Accepted: 6 August 2010
Published: 6 August 2010
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Pre-publication history
The pre-publication history for this paper can be accessed here:
http://www.biomedcentral.com/1472-6882/10/44/prepub
doi:10.1186/1472-6882-10-44
Cite this article as: Shin et al.: Maca (L. meyenii) for improving sexual
function: a systematic review. BMC Complementary and Alternative
Medicine 2010 10:44.
Shin et al. BMC Complementary and Alternative Medicine 2010, 10:44
http://www.biomedcentral.com/1472-6882/10/44
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