Horny goat weed is an ornamental plant that also has a long history of traditional use in Asian herbal medicine. Its whimsical name is said to derive from folk observations that goats who grazed on the herb became unusually sexually active. Horny goat weed is said to “tonify the kidney yang”; this is an expression whose meaning cannot be fully explained without entering into the theoretical framework of Traditional Chinese Medicine, but in a loose sense it signifies warming and invigorating the core energy of the body. Traditional uses of the herb (generally in formulas involving several other herbs as well) include treatment of male sexual dysfunction, prostate and urinary problems, low back pain, knee pain, poor memory, emotional timidity, and general symptoms of aging. The above-ground portion of the plant is used medicinally.

What Is Horny Goat Weed Used for Today?

Horny goat weed is currently marketed as a sexual stimulant for both men and women, and also as a treatment for menopausal symptoms. However, there is no meaningful scientific evidence to support these proposed uses. Statements on multiple websites claim that it increases testosterone levels, inhibits acetylcholinesterase (a chemical important in the function of the nervous system), and has been shown to act as an aphrodisiac in mice. However, the references cited on these sites do not support these statements. What limited scientific is available is at best is far too preliminary to prove anything at all.1-9

According to test-tube studies and preliminary human trials, a different species in the same family, Epimedium brevicornum, may have estrogenic activity.10-12,16 However, even if this were to apply to horny goat weed as well, it would not indicate effectiveness for menopausal symptoms. Many herbs with estrogenic effects in the test tube do not appear to help menopausal symptoms (Interestingly, the one herb that most reliably appears to affect menopausal symptoms, black cohosh, does not have estrogenic effects in the test tube.)

A study of yet another distinct species, Epimedium koreanum, seems to be the source of the widespread claim that horny goat weed affects acetylcholinesterase.13

In fact, only double-blind, placebo-controlled studies can begin to prove a treatment effective, and none have been performed on horny goat weed taken by itself. The only study of this type tested a combination of horny goat weed, maca, Lepidium meyenii, Mucuna pruriens, and Polypodium vulgare.14 It supposedly found benefit, but its design and reporting were markedly inadequate, and the results are unreliable.

Dosage

A typical dose of horny goat weed is 250-1,000 mg daily.

Safety Issues

The safety of horny goat weed is unknown. There is one case report in which use of a horny goat weed product caused rapid heart rate and manic-like mood changes in a 66-year-old man.15 It is not clear whether the herb itself caused the symptoms, as it is possible the product used by this individual might have been adulterated or contaminated with an unlisted active substance.

Safety in young children, pregnant or nursing women, or people with severe liver or kidney disease has definitely not been established.