Icariin
syn. Horny Goat Weed (extract) syn. Epimedium extract
Description:
Icariin is a natural flavonoid compound found in several herbaceous plants of the epimedium species (commonly known as Horny Goat Weed). Epimedium extracts have a long history of use in traditional Chinese medicine, where they have been widely applied to treat erectile dysfunction and increase male libido. They have also been used to treat numerous other medical conditions including cough, asthma, high blood pressure, and heart disease. In sports nutrition, epimedium extracts (standardized for icariin) are promoted to increase male testosterone levels and improve exercise performance. Common sources of icariin specifically include extracts of epimedium sagittatum, epimedium grandiflorum, and epimedium brevicornum.
Modern studies suggest icariin has a broad range of biological activity. For example, animal studies have shown icariin to support erection via a nitric oxide simulating and phosphodiesterase (PDE5) inhibiting effect, similar to the prescription drugs sildendafil and tadalafil.427,428 Other animal studies have shown icariin to counter some of the negative metabolic effects of stress, specifically reducing levels of cortisol and the inflammatory mediators interleukin-6 (IL-6) and tumor-necrosis-factor alpha (TNF-alpha).429 This could have a number of positive health implications. Additionally, icariin seems to possess antioxidant430 and bone-strengthening properties.431 It may also possess some estrogenic activity.432,433 Studies on the effects of epimedium extracts on serum androgen levels have been conflicting, however, and it is unknown if icariin possesses tangible ergogenic value.
Promoted Benefits:
Icariin is promoted to increase testosterone levels and support the anabolic effects of resistance exercise.
Clinical Studies:
The use of icariin as a sport supplement is supported by animal data only. Its Clinical Support Rating is 2 (2/5).
One of the most widely cited studies on icariin examined its effects on sexual function and serum androgen levels in male rats. The experiment involved drug-induced damage to the reproductive system, followed by supplementation with either icariin (200 mg/kg daily) or testosterone (5 mg per day). Icariin was shown to increase serum testosterone levels, and improved other variables including bone resorption and reproductive organ condition in a similar manner as subcutaneous testosterone injection.
Other clinical studies have had conflicting results, however, showing epimedium extracts and icariin to have no effect on serum testosterone levels.434,435 No peer reviewed placebo-controlled human studies examining the effects of this supplement on androgen levels or exercise performance have been published. Further research is needed to determine if icariin has testosterone stimulating or ergogenic effects in humans.
Empirical Evidence:
Icariin (in the form of standardized epimedium extracts) is widely available as a stand-alone nutritional supplement. The feedback on its use as a sport supplement has been very mixed. A majority of users do seem to report erectile stimulating properties, and icariin supplements (usually marketed as Horny Goat Weed) are commonly used in male aphrodisiac and erectile dysfunction treating supplements. This, however, has not translated into common anecdotal reports of high testosterone elevations or noticeable muscle gain / improved exercise performance. While some users do report such activity, the frequency is too low to consider this a positive trend. Icariin has an Empirical Evidence Rating of 3 (3/5).
Effective Dosage:
An effective dosage of this supplement has not been established. Manufacturers commonly recommend 50-200 mg of icariin per day. Note that there are many different extracts of varying purities, which makes evaluating and dosing this supplement somewhat difficult.
Side Effects / Safety:
Icariin appeared to be well tolerated during clinical studies, with no significant toxicity or side effects reported.436
