Horny Goat Weed

The leaves of various species of epimedium have been used as the herb known as yin yang huo, which literally translates as horny goat weed, in traditional Chinese medicine. The various species grow naturally from southern central to northern coastal China as well as Korea. Other species of epimedium are found in many parts of the world, though their similarity to horny goat weed is uncertain.

Horny goat weed has played a vital, multifaceted role in traditional Asian medicine for at least 1,000 years. It is considered a yang tonic, particularly for the "energetic organ" known as the kidney (which corresponds to some extent to the Western concept of the kidney). Enhancing kidney energy in this setting correlates to improving sexual function and fertility.¹ Animal studies conducted in China have investigated the use of this herb within the traditional conception of a yang tonic and found effective for that purpose.² It is also considered helpful for combating what is known as wind-damp-cold blocking circulation of the body’s dynamic life energy, or qi, which in Western terms is similar to hardening of the arteries and related complications. It is particularly used to help people recover from strokes.

In most cases, herbs in traditional Asian medicine are not used singly, but rather as a component of multiherb formulations. One animal study in China found that a combination of horny goat weed and three other herbs was effective at reducing osteoporosis resulting from the use of cortisone-like drugs, but none of the four herbs used alone was effective.³ This finding supports the traditional notion that horny goat weed may be particularly beneficial when used in combination with other herbs.

Horny goat weed contains a number of flavonoids, some of which show estrogen-inhibiting properties in the test tube.⁴ These hormonal actions may be part of the reason horny goat weed has been used traditionally to treat sexual disorders, and why it has shown efficacy in clinical trials in patients with kidney failure for improving sex drive.⁵ Other flavonoids in horny goat weed, such as icariin, appear to stimulate the cells that build bone (osteoblasts).⁶ Rats given flavonoid extracts of horny goat weed are protected against osteoporosis.⁷ A number of flavonoids showed effects on the immune system that are both stimulating and suppressing depending on the circumstances in the test tube.⁸ Preliminary human trials in people with kidney disease undergoing dialysis confirm that horny goat weed can improve the function of various portions of the immune system.⁹ Icariin protects liver cells in the test tube.¹⁰

A water extract of horny goat weed has been shown to inhibit growth of new blood vessels, a property potentially useful in stopping the growth of cancerous tumors.¹¹ Extracts of the herb were moderately effective at inhibiting growth of cancer cells in the test tube, though icariin by itself was not.¹² Icariin was effective at causing some cancer cells to become more normal in the test tube.¹³

Lignans have also been found in various species of horny goat weed. Some lignans have been shown in one animal study to stimulate nerve growth.¹⁴

A combination of horny goat weed with three other herbs has been shown to inhibit inflammation in several animal studies.¹⁵ This might in part explain the observed utility in early studies on the use of horny goat weed–containing formulas in people with hay fever.¹⁶ The immune effects of the flavonoids might also be relevant here.

A water extract of the whole herb of horny goat weed was shown to strongly inhibit a herpes simplex virus in the test tube.¹⁷ Water extracts of horny goat weed have also been shown to reduce blood pressure in several animal species and to reduce cholesterol levels.¹⁸ These extracts have been reported to be helpful in combination with several other herbs in people with what is described in Chinese medicine as kidney yang deficiency, presenting as what would be called in the West hardening of the arteries to the brain leading to dementia.¹⁹ This formula was more effective than one not containing horny goat weed. The effectiveness was correlated with antioxidant, cholesterol-lowering, and anti-inflammatory effects seen in the people taking the horny goat weed–containing formula.

Traditionally 5 grams (1 tsp) of horny goat weed was taken three times per day, usually after being simmered (decocted) in 250 ml (1 pint) of water for 10 to 15 minutes.²⁰ A similar amount can be taken in the form of granules, which are freeze-dried grains made from decocted herb, or powdered herb in capsules.

In traditional Chinese medicine, horny goat weed is usually combined with yin tonic herbs when used long term for support of sexual health.²¹ If this is not done, it is believed the herb could cause problems such as aggressiveness, irritability, fever, or other “hot” symptoms (such as racing heart beat). In animal studies, prolonged use of excessive amounts of horny goat weed was associated with decreased thyroid activity.²²