Horny Goat Weed

Horny Goat Weed

What Is It?

Horny goat weed is an over-the-counter herb with the active ingredient Icariin, an extract of Epimedium, a genus of flowering plants in the family Berberidaceae [21]. It is used in traditional Chinese medicine to treat fatigue, arthritic pain, nerve pain, and sexual dysfunction [22].

How Does It Work in the Body?

The active ingredient in horny goat weed is Icariin, a weak phosphodiesterase type 5 (PDE5) inhibitor, allowing blood to fill the arteries and the three cylinders in the penis and create an erection [23, 24].

What Is It Used for?

Horny goat weed is traditionally used in herbal formulas for sexual dysfunction, due to its weak PDE5 inhibition. However, additional research is needed to verify such effects [22].

Epimedium is traditionally used for fatigue, but it has not been studied in clinical trials [22].

A small, randomized trial shows that Epimedium may help prevent bone loss in women who have had menopause for a long time [22].  

Precautions/Side Effects:

Excessive dosages of horny goat weed may cause diaphoresis (sweating) and hot flashes—however, safety evaluations are scarce [22, 25].

Evidence for and Against:

As per Shindel et al., rats treated with low-dose icariin (ICA) demonstrated significantly higher intracavernous pressure/mean arterial pressure (ICP/MAP) and area under the curve/mean arterial pressure (AUC/MAP) ratios compared with control and single-dose ICA animals. Immunohistochemistry and Western blot were revealing of significantly greater positivity for neuronal nitrous oxide synthase (nNOS) and calponin in penile tissues of all rats treated with ICA. ICA led to significantly greater neurite length in cultured specimens of pelvic ganglia [24].  

A case study of an elderly man with congestive heart failure presenting with shortness of breath, angina, and new-onset symptomatic arrhythmia after taking horny goat weed daily for 2 weeks to increase sexual pleasure. The side effects and drug interactions of horny goat weed are difficult to interpret considering variability in the contents of herbal formulations. Herbal products may contain a host of other pharmacologically active substances, including coumarins, glycosides, alkaloids, and flavonoids, some of which have been demonstrated to inhibit cytochrome P450 enzymes [22, 26].

Dosage:

There is no FDA recommended dosage for horny goat weed other than the recommended serving size as set by the manufacturer [23].

Thus, the amount of horny goat weed varies—generally 500 to 1000 mg per serving—depending on the brand [23].

Interactions:

Prolonged use of Epimedium can induce CYP3A4 through the activation of pregnane X receptor. The clinical relevance is unknown [22].

Icariin enhances the action of aromatase, which may reduce the effect of aromatase inhibitors, like anastrozole, exemestane, and letrozole. The clinical relevance is unknown