What Is Horny Goat Weed?

Horny goat weed, also known as Epimedium, yin yang huo, or herbal “Viagra,” is a plant used in traditional Chinese medicine.

As its name suggests, horny goat weed is purported to improve sexual function by increasing blood flow to the penis. Because it contains phytoestrogens (compounds that act like estrogen), horny goat weed has been studied for osteoporosis (weak and brittle bones), a condition common in people undergoing menopause.

This article discusses the possible uses, side effects, precautions, and other safety concerns of horny goat weed.

Uses of Horny Goat Weed

The main studies on horny goat weed were conducted in vitro (in test tubes) or in animal studies. Erectile dysfunction and bone disorders are the two most commonly studied conditions.

Other potential health benefits (limited to animal and/or test tube studies) of horny goat weed or its main components (natural chemical compound) include the following:

• Osteoarthritis
• Asthma
• Premenstrual syndrome and menopausal symptoms
• Cardiovascular disease
• Alzheimer’s disease
• Depression
• Parkinson’s disease
• Multiple sclerosis

Erectile Dysfunction

Human clinical studies are lacking, but preliminary evidence suggests icariin, a chemical compound in horny goat weed, inhibits a protein linked with erectile dysfunction called phosphodiesterase type 5 (PDE5).

Phosphodiesterase-5 inhibitors, such as horny goat weed and Viagra, widen the blood vessels, increasing blood flow to the penis needed for an erection. Erectile dysfunction occurs when there is not enough blood flowing to the penis.

A systematic review noted that horny goat weed was one of the most common ingredients in testosterone and erectile dysfunction supplements. 

Further human studies are needed to determine the efficacy of horny goat weed for erectile dysfunction.

Bone Loss

A study in postmenopausal individuals showed horny goat weed extract increased the activity of bone-forming cells and decreased bone breakdown. The study was limited because it was unclear if changes in biomarkers would translate to clinical efficacy. 

The bone-protective effect of icariin, the main active component in horny goat weed, is due to its estrogenic activity based on animal models.

Furthermore, another clinical trial showed icariin prevented bone loss compared to a placebo. Both groups were also given 300 milligrams (mg) of elemental calcium daily. Since the treatment group consisted of icariin and other sources of phytoestrogens, the effect of icariin alone on osteoporosis was unclear.

What Are the Side Effects of Horny Goat Weed?

Despite the promising results, horny goat weed may have potential side effects. These side effects may be common or severe.

Common Side Effects

A randomized, double-blind, placebo-controlled trial evaluating the safety of horny goat weed in 58 postmenopausal people reported no side effects during the 8-week observational period.

However, a review reported the following side effects:

• Mood changes
• Anxiety
• Hallucinations

Severe Side Effects

One clinical trial evaluating the effect of horny goat weed on estrogen levels and fat metabolism in postmenopausal participants showed no significant side effects of horny goat weed.

Additionally, horny goat weed was not linked with endometrial hyperplasia (irregular thickening of the uterine wall).

Stop taking horny goat weed if you have any signs of an allergic reaction.

If you're having a severe allergic reaction or if any of your symptoms feel life-threatening, call 911 and get medical help right away.

Precautions

Certain people should not take horny goat weed:

• People who are pregnant or breastfeeding
• People with bleeding disorders (horny goat weed might slow blood clotting and thus make bleeding disorders worse; since horny goat weed can slow blood clotting, avoid using it before surgery)
• Individuals with heart disease (horny goat weed may cause rapid, irregular heartbeat)
• People with hormone-sensitive cancers and conditions such as breast cancer, uterine cancer, and endometriosis (horny goat weed acts like estrogen and can increase estrogen levels)

Dosage: How Much Horny Goat Weed Should I Take?

Although the standard dose of horny goat weed is unclear, the doses used in some clinical trials are noted below. 

Osteoporosis: In one trial of people in postmenopause, two 370 milligram capsules of horny goat weed extract (48.2% prenylflavonoids and 6.9% icariin) daily for six weeks. In another trial, 60 milligrams of icariin, 15 milligrams of daidzein, and three milligrams of genistein--and 300 milligrams (mg) of elemental calcium daily--were used.

What Happens If I Take Too Much Horny Goat Weed?

Horny goat weed extract containing phytoestrogens has been safely taken by adults by mouth for up to two years. Another extract containing icariin has been taken safely for up to six months.

Using certain types of horny goat weed for a prolonged period or at higher doses is possibly unsafe. Serious side effects, such as severe breathing problems, have been reported.

Interactions

Use horny goat weed with caution if you take the following medications:

• Estrogens: Horny goat weed might increase the effect of estrogen. 
• Blood Pressure Lowering Medications: Taking horny goat weed with medications that lower blood pressure might cause blood pressure to go too low. 
• Blood Thinners: Taking horny goat weed with medications that slow blood clotting might increase the risk of bruising and bleeding.

It is essential to carefully read a supplement's ingredient list and nutrition facts panel to know which ingredients and how much of each ingredient is included. Please review this supplement label with your healthcare provider to discuss potential interactions with foods, other supplements, and medications. 

How to Store Horny Goat Weed

Storage instructions vary for different products. Carefully read the directions and packaging label on the container. Keep your medicines tightly closed and out of the reach of children and pets, ideally locked in a cabinet or closet. Try to store your medications in a cool and dry place.

Similar Supplements

In addition to horny goat weed, other supplements suggested to improve erectile dysfunction (although evidence is limited) include the following:

• L-Arginine
• Panax ginseng
• Tongkat ali
• Tribulus terrestris
• Maca
• Yohimbine (as an extra treatment with other supplements)

Whereas horny goat weed, L-arginine, and Tribulus terrestris improve erectile dysfunction by increasing the production of nitric oxide (a compound that widens blood vessels and increases blood flow to the penis), tongkat ali seems to increase testosterone levels. Panax ginseng has been reported to increase nitric oxide production and testosterone levels. The mode of action for maca is unknown. Yohimbine blocks alpha-2 adrenoreceptors, which are the receptors responsible for inhibiting erection.

It is not uncommon to find products containing a combination of horny goat weed and other supplements suggested to improve erectile dysfunction.

Sources of Horny Goat Weed & What To Look For

Horny goat weed can be found in drug and health-food stores and is available as a supplement under the scientific name Epimedium. Additionally, some products specify the amount of icariin (the active substance in horny goat weed) on the label. 

Look for a product with a seal of approval from a third-party organization that provides quality testing. These organizations include U.S. Pharmacopeia, ConsumerLab.com, and NSF International.

A seal of approval from one of these organizations does not guarantee that the product is safe or effective. But it does assure you that it was made correctly, contains the ingredients listed on the label, and does not contain harmful contaminants.

It is important to note that supplements with some of the most significant risks of contamination are the ones promising sexual enhancement.

Before taking a horny goat weed supplement, talk to your healthcare provider.

Horny Goat Weed Supplements

Horny goat weed is available as a capsule, tablet, powder, or tea.

While horny goat weed supplement is available as a single active ingredient, it can be found in combination with other supplements purported to improve erectile dysfunction. 

Summary

Horny goat weed is an herbal supplement that some people use as a kind of "natural Viagra" to treat erectile dysfunction. Some studies suggest that it has other positive effects, especially bone health. However, more rigorous human clinical studies are needed to clarify the health benefits of horny goat weed.

Caution should be taken if you have certain medical conditions or take certain medications. Consult your healthcare provider to determine if a horny goat weed supplement is right for you.