Q&A 385.2
Does horny goat weed work for erectile dysfunction?
Prepared by UK Medicines Information (UKMi) pharmacists for NHS healthcare professionals
Before using this Q&A, read the disclaimer at
Date prepared:15th November 2013
Background
Horny goat weed (Epimedium brevicornu Maxim., HGW) is a herbaceous flowering plant found mainly in China and Asia[1]. Traditionally it has been used as an antirheumatic, a tonic, and to improve bone health. Currently it is more commonly used to treat sexual dysfunction such as impotence and involuntary ejaculation[2].
There is some confusion among the different sub species of horny goat weed used as herbal medicines. Usually, a mixture of species is used in Chinese traditional medicine2.
In common with most herbal medicines, many of the active constituents, and their pharmacological relevance, remain largely unknown. It is thought, however, that most of the active constituents are prenylated flavonoids and isoflavones. Of these, the most relevant are icariin, epimedin A, B and C and 6prenylchrysin2
Answer
There are currently no clinical trials in humans assessing the use of HGW for erectile dysfunction.
One study using isolated rat cavernous smooth muscle cells showed that the icariin component of HGW did have an inhibitory effect on phosphodiesterase-5 (PDE-5). This is the same enzyme that conventional erectile dysfunction drugs such as sildenafil and tadalafil, and vardenafil act upon. In this study, HGW was found to be a less potent inhibitor of PDE5 than Zaprinast. Zaprinast is the compound that both sildenafil and vardenafil are derived from[3]. This probably means that horny goat weed is a less potent inhibitor of PDE5 than either sildenafil or vardenafil although no direct comparisons have been performed.
A further in-vitro study looked at the effects of two isolated components of HGW (icariin and noricariin), on rabbit corpus cavernosum. This study found that these extracts elicit their effect by acting on multiple targets including nitric oxide, cyclic GMP and PDE-5. This provides evidence of a potential mechanism that may mean these isolated components have the potential to be effective in erectile dysfunction, particularly alongside conventional PDE-5 inhibitors, although interestingly, the authors noted a decrease in potency [4]
An in vivo study in rats showed improved sexual behaviour in male rats when they where treated with a Chinese herbal medicine preparation which contained leaves from the epimedium family of plants along with four other herbs. This study found that in combination these herbs did improve sexual function in rats, with particularly marked results in those rates described as “sexually sluggish or impotent”. However when each of these herbs were tested individually there was no improvement in sexual function. The writers postulate there must be some sort of synergistic action between these herbs.[5]
In all of the studies examining HGW use for erectile dysfunction, refined components of have been used. This is unlikely to reflect real-world use of this complementary therapy, particularly where non-standardized dried plant components are consumed. This may further reduce potential efficacy of this product.
Summary
There is limited evidence for the effectiveness of components of HGW in the treatment of erectile dysfunction.
No studies in humans were located. In the above animal studies, 2 were in vitro experiments and one was in vivo in the rat, limiting the usefulness of this data in relation to humans. Although the studies seem to suggest a potential effect for some components of HGW, it appears to be weakly active at inhibiting the PDE-5 enzyme.
Limitations
This Q&A considers only the treatment of erectile dysfunction with HGW. The amount of good quality information available about herbal medicines in general is often limited due to the lack of regulation of these products. All of the currently available information is from in vitro studies so application of the data to in vivo human use is difficult.
Quality Assurance
Prepared by
Vincent Cassidy, Regional Drug Therapeutics Centre, Newcastle upon Tyne
Date Prepared
15th November 2013
Checked by
Hayley Johnson, Regional Drug & Therapeutics Centre, Newcastle upon Tyne
Date of check
2nd January 2014
Search strategy
Embase
exp EPIMEDIUM OR exp ICARIIN AND exp IMPOTENCE
Medline
exp EPIMEDIUM OR exp ICARIIN AND exp IMPOTENCE
In-house database/ resources
References
1
Available throughNICE Evidence Search at
[1] Epimedium: The Royal Horticultural Society. Accessed on 8th November 2013 at
[2] Epimedium Monograph: Williamson E, Driver S, Baxter K (eds), Stockley's Herbal Medicines Interactions. [online] London: Pharmaceutical Press. < (accessed on 8th November 2013).
[3] Ning H, Xin ZC, Lin G et al Effects of icariin on phosphodiesterase – 5 – activity in vitro and cyclic guanosine monophosphate level in cavernous smooth muscle cellsUrology. 2006 Dec;68(6):1350-4.
[4] Chiu JH, Chen KK, Chien TM, et al Epimedium brevicornum Maxim extract relaxes rabbit corpus cavernosum through multitargets on nitric oxide/cyclic guanosine monophosphate signalling pathway. International journal of impotence research 2006 (18) 335-342
[5] Zanoli P, Benellia A, Zavatti M et al, Improved sexual behaviour in male rats treated with a Chinese herbal extract: hormonal and neuronal implications. Asian journal of anronology 2008 10 (6): 937-945