Evidence Based
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11 Scientific Horny Goat Weed Benefits + Dosage, Side Effects

Written by Randa Laouar, BS (Biochemistry & Physiology) | Reviewed by Ana Aleksic, MSc (Pharmacy) | Last updated:
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology) | Written by Randa Laouar, BS (Biochemistry & Physiology) | Reviewed by Ana Aleksic, MSc (Pharmacy) | Last updated:

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Libido and sexual health

Companies that advertise “natural” sexual health supplements make a lot of tantalizing claims, especially when they’re pitching male libido enhancement. One such popular herb has a funny name: horny goat weed. Used to boost sex drive for millennia, some even call it a natural Viagra. To investigate if there is any truth to the purported claims, we set out to compile the scientific evidence and discovered other potential benefits and risks along the way.

What Is Horny Goat Weed?

Horny Goat Weed (Epimedium) is a flowering plant that has been used as a natural aphrodisiac in Chinese traditional medicine since ancient times. Legend has it that its whimsical name originates from the observations of a goat herder, who noticed that his herd became more sexually active after grazing on the Epimedium that grew near the fields [1, 2, 3+].

Also known as rowdy lamb herb, barrenwort, bishop’s hat, fairy wings, and yin yang huo, the term “Epimedium” refers to a genus of 52 species of herbaceous plants, with E. koreanum, E. sagittatum and E. brevicornum most frequently used for medicinal purposes [3].

Horny goat weed is commonly used for problems related to sexual performance, such as erectile dysfunction (ED) and low libido. It is also used for lower back, knee and joint pain, arthritis, mental and physical fatigue, and memory loss along with many other conditions [3].

But does it really work, according to the evidence?

Currently, there are limited clinical studies on horny goat weed. However, anecdotal observations, coupled with some evidence from animal and cellular studies, suggests that horny goat weed may [3]:

  • Increase testosterone production
  • Increase estrogen levels, particularly in post-menopausal women
  • Improve libido
  • Promote blood circulation
  • Normalize cortisol levels, a stress hormone that can depress the sex drive
  • Prevents bone loss

Most of these benefits were due to its active component, icariin. However, pure horny goat weed doesn’t actually contain enough icariin to yield any measurable effects. This also means that drinking herbal tea from it is unlikely to have any aphrodisiac benefits [2].

Nowadays, newer formulations of horny goat weed are standardized to contain more icariin. Despite this, icariin has poor bioavailability and has to be modified to be better absorbed when taken orally [2].

Snapshot

PROs

  • May boost libido and help with ED
  • May protect the brain and enhance cognition
  • May help with menopausal symptoms and enhance bone health
  • Potentially balances the immune system

CONs

  • Not all supplements contain enough of its active compounds
  • Many benefits have not been clinically investigated
  • Can interact with medications
  • Long-term effects are unknown

Components

So far, scientists isolated more than 250 compounds from horny goat weed. Some of these include [4, 3+, 5]:

  • Icariin, the prenylated glycoside flavonoid known as the active ingredient, and other flavonoids (i.e. quercetin, epimedin A, B, and C). Total flavonoids, especially icariin, are its defined quality indicators in the “Chinese Pharmacopoeia
  • Icariin derivatives (such as icaritin, icariside I and II)
  • Polysaccharides – complex carbohydrates with anticancer, antioxidant, and immune-boosting effects
  • Magnoflorine, an alkaloid with antioxidant, anti-inflammatory, and anti-cancer properties

Mechanism

Similar to Viagra or Cialis, horny goat weed mainly works by increasing blood flow to the genitals, which can increase arousal. Its active component icariin does this by inhibiting phosphodiesterase-5 (PDE5), an enzyme that restricts blood flow throughout the body, including the penis. This results in an inflow of blood to the penis, leading to an erection [6].

But, compared to other drugs on the market, icariin is weak PDE5 inhibitor. Viagra (sildenafil), for example, is 80 times more effective at inhibiting PDE5 than icariin. In one study, however, scientists were able to modify the structure of icariin and obtain a derivative with similar activity to Viagra. Because this compound targeted the enzyme more precisely, it may have fewer side effects [7].

Icariin also [8, 2, 9, 10]:

  • Crosses the blood-brain barrier, where it may have neuroprotective effects
  • Enhances brain function by improving brain blood flow, synaptic plasticity, brain blood vessel health, and beta-amyloid elimination from regions of the brain important for memory and cognition (the hippocampus and cortex)
  • Reduces inflammation by lowering pro-inflammatory molecules (TNF-alpha, IL-B, as COX-2). It also blocks a key inflammatory pathway called NF-κB
  • Reduces oxidative stress by increasing superoxide dismutase (SOD), an enzyme that reduces oxidative damage and increases antioxidant defense
  • Protects bones by increasing a protein that helps form bones and cartilage (called bone morphogenetic protein, BMP-2). It also enhances the production of osteoblasts, cells that build and repair bones
  • May increase estrogen in menopausal women
  • May boost testosterone

Health Benefits

The majority of the benefits of horny goat weed refer to its active ingredient, icariin.

1) Erectile Dysfunction and Libido

Erectile dysfunction (ED) is the inability to get and maintain an erection sufficient to achieve satisfactory sexual performance. It’s also known as impotence. ED can be occasional or frequent and has various causes, both psychological and physical. Since erections depend on healthy blood flow to the penis, problems that reduce blood flow in the penis can trigger ED [11, 12].

Icariin, the active component of horny goat weed, improved erectile function in old, diabetic, and castrated rats. These effects may be linked to its ability to promote blood flow throughout the body [13, 14, 15].

Another study found that male rats with damaged penile nerves had improved erectile responses after icariin [1].

Horny goat weed may also enhance libido. In a study of 22 people with chronic kidney disease, it improved sex drive and quality of life [16].

What’s more, low testosterone may reduce sexual desire in both men and women. In rats, icariin increased free testosterone levels. Although this effect was not researched in humans, it suggests that horny goat weed’s aphrodisiac action may be tied to its ability to boost testosterone, especially in older people [17, 18, 19].

2) Mood Disorders

In a pilot study of ten depressed people with bipolar disorder and alcohol addiction, doses of icariin of up to 300 mg/day for 8 weeks reduced depressive symptoms and alcohol drinking. It was tolerated well and no side effects were reported [20].

Additionally, icariin normalized levels of stress hormones cortisol and CRF in depressed rats under chronic mild stress. CRF is the first hormone of the HPA axis and plays a huge role in triggering off your stress response. High CRH levels may contribute to anxiety, depression, emotional imbalances, and memory problems [21, 22, 23, 24].

Inflammation is closely tied to HPA overactivity when it comes to stress resilience and emotional balance. In the above study, icariin also lowered inflammatory markers, which were high in stressed rats (e.g. IL-6 and TNF-alpha). Overall, it certainly has an interesting mood-balancing potential, but more studies are needed [21].

3) Menopause

Flavonoids like icariin in horny goat weed can act as phytoestrogens, plant compounds that mimic the effects of female sex hormones. In one clinical trial of 90 postmenopausal women, an extract of horny goat weed increased estrogen levels and lowered cholesterol levels [25, 26].

Aside from its beneficial effects on hormone levels, horny goat weed didn’t cause any significant side effects. This herb may be researched further as a natural alternative to hormone replacement therapy in women after menopause [26].

4) Cognition

Horny goat weed’s active ingredient, icariin, may protect the brain by reducing excessive oxidative stress and inflammation, which often underlie cognitive dysfunction. Additionally, it may help eliminate beta-amyloid peptides, protein fragments that build up as clumps in the brain and disrupt cell communication. In animal and lab studies, icariin [27, 28]:

  • Improved dementia in rats by reducing oxidative damage and beta-amyloid clumps in the brain’s memory hub, the hippocampus. This brain region is also involved in mood balance and connected to other emotional and cognitive centers in the brain
  • Protected again the neurotoxic effects of aluminum in rats, preventing memory loss
  • Improved spatial learning and memory in rats with brain inflammation

Although horny goat weed is rarely talked about in terms of cognitive enhancement, it may activate some crucial brain-protective mechanisms. These have yet to be researched in humans, so we can’t say if it truly acts as a hybrid nootropic aphrodisiac. Based on the studies in cells and animals, icariin also [29, 30, 31, 32]:

  • Lessened cognitive decline in rats by increasing BDNF and its receptor. BDNF is a brain-growth protein (neurotrophic factor) involved in cognition and synaptic plasticity
  • Prevented cognitive deficits in rats with stroke by preventing a drop in acetylcholine, a neurotransmitter that is key for learning and memory. It also prevented low levels of enzymes that make and break down acetylcholine, which suggests it may be able to balance cholinergic activity rather than just boost it. Interestingly, its effects were also specific to the hippocampus in this study

Some scientists consider it should be further explored for its potential to protect brain cells from toxins and poor circulation. On the other hand, these brain-protective properties may be linked to the herb’s libido and moodenhancing benefits.

5) Energy & Endurance

Many libido-enhancing herbs also boost energy and exercise performance; maca is a well-known one. Horny goat weed, too, might boost energy levels and reduce fatigue. In mice, icariin reduced physical fatigue and increased endurance during a weight-loaded swimming test [33].

Many people seek horny goat weed just for an energy boost. It’s also possible that this herb’s sexual benefits are amplified by its ability to energize and boost endurance. And while it is commonly used to overcome fatigue and low energy, the scientific evidence for these benefits is still weak.

6) Immunity and Autoimmune Disorders

Horny goat weed plays a multifaceted role in the immune system. It acts as an immune modulator, which means that it can both stimulate and suppress the immune system, depending on what’s causing an imbalance. Additionally, it might be able to directly reduce the growth of viruses.

For example, in a lab study, a water extract of horny goat weed strongly inhibited the virus that causes genital herpes (HSV-2) [34].

Additionally, icariin increased a protein that helps recognize disease-causing microorganisms (TLR9) in mouse immune cells. This protein can activate the immune system and helps fight infections [35].

In mice, icariin also enhanced the Th1 immune response, which should also help fight infections. This may be beneficial for people who have weak immune systems but would usually be considered detrimental in people with immune overactivity, such as those with autoimmune diseases [36].

In that case, does icariin worsen autoimmunity?

On the contrary. Although most substances either increase or decrease specific responses (Th1, Th2, Th17), icariin may be more versatile and balancing. According to animal studies, it may suppress an overactive immune system too. It improved symptoms in mice with multiple sclerosis by suppressing Th1 and Th17 autoimmune reactions and lowering inflammation [37].

The key to its immune-soothing properties may lie in immune cells called Tregs. Tregs suppress harmful activated immune cells such as Th1, Th2, and Th17. They play the role of “immune system peacekeeper” that calms other immune cells when they overreact. In one study on mice with asthma, icariin reduced airway inflammation and narrowing by regulating Tregs (and Th17 cells) [38].

7) Heart Disease

Because it may reduce blood cholesterol levels and oxidative stress, horny goat weed may also protect the heart. In one study, horny goat weed granules given to 120 older people with heart disease and kidney problems relieved symptoms and improved heart health. They were more effective than the control placebo-like formula [39].

Additionally, in animal studies, icariin [40, 41, 42, 43, 44]

  • Improved function and reduced damage to the heart in rats with heart attacks; it may work by increasing the survival of heart cells in harsh, low-oxygen circumstances
  • Reduced oxidative damage in the mitochondria of diabetic rat hearts. The mitochondria are extremely important for the heart’s high energy demands and their damage is the hallmark of heart and blood vessel diseases, as well as diabetes
  • Lowered cholesterol levels, reducing the risk of excessive blood clotting in rabbits with hardening of the arteries, or atherosclerosis

8) Bone Health

Icariin may help maintain healthy bones by enhancing bone building and growth and preventing bone breakdown and loss.

In one clinical trial, an herbal regimen containing epimedium-derived flavonoids prevented bone loss in 74 postmenopausal women. Its flavonoids can have estrogen-like effects, which are desirable in women after menopause. Importantly, this herbal regimen didn’t have any negative effects on the uterine lining [45].

In lab and animal studies, icariin and its sister compounds [46, 47, 9, 48]:

  • Improved bone mineral density and strength in menopausal rats
  • Increased bone-building cells (osteoblasts)
  • Lowered bone-degrading cells (osteoclasts)
  • Reduced harmful free radicals
  • Prevented cartilage and bone breakdown in arthritic mice

9) Cancer

Horny goat weed has some cancer-fighting potential, but research has not gone beyond cell-based studies. In these, icariin and its derivatives blocked the growth of cancer cells in the bone, prostate, lung, stomach, and kidney [5].

Its active compounds may act in a variety of ways, including [5]:

  • Causing cancer cells to commit suicide (apoptosis)
  • Preventing the growth of blood vessels that feed tumors with oxygen and nutrients (angiogenesis)
  • Blocking the spread of cancer cells (metastasis)

These studies are preliminary and it’s much too early to say whether horny goat weed might have any cancer-fighting benefits in humans.

10) DNA and Aging

Many compounds in horny goat weed may act as cell-protective antioxidants, so it’s possible that they may support longevity. In a cell study, icariin protected DNA by reducing oxidative stress [49].

Icariin may activate anti-aging pathways, but the extent to which this holds true in humans is unknown. For example, in mice, it delayed aging by increasing an enzyme called SIRT6. SIRT6 promotes DNA repair and energy metabolism and inhibits the NF-kB pathway, which is involved in inflammation, the aging of cells, and their death [50].

Icariin and its derivative also delayed aging in worms by promoting oxidative stress resistance, muscle function and movement, and preventing toxic protein buildup [51].

11) Acne

In a cell study, horny goat weed extracts and icariin blocked one bacterium that causes acne (Propionibacterium acnes) from creating biofilms, in part by directly killing the bacterial cells. Biofilms are created when bacterial cells stick together closely and are especially hard to destroy [52].

With more research, creams from horny goat weed might be available for human use. At the moment, this herb is only used orally.

Limitations and Caveats

Unfortunately, most of what is known about horny goat weed comes from lab and animal studies. Although scientists discovered that its mechanisms are similar to viagra, large clinical trials on men with erectile dysfunction or in people with other types of sexual dysfunctions have not been investigated. Clinical trials are needed to establish the effectiveness of this popular herb.

Side Effects & Precautions

Common side effects may include [2]:

  • Upset stomach
  • Dry mouth
  • Fever
  • Increased heart rate
  • Aggressiveness
  • Irritability

Horny goat weed users also report some of these side effects. The quality of the product, dosage, and individual sensitivity to its contents all determine the side effects profile.

A couple of people who used horny goat weed experienced more serious side effects. It’s unknown what additional medications they were taking, which is especially important since this herb can interact with drugs. Read more about these in the drug interactions section below.

In one case report, a 77-year-old man experienced rashes, pain and burning sensations after taking horny goat weed with ginkgo to improve his memory and libido [53].

In another case report, a 66-year-old man with a history of heart disease experienced a rapid heart rate (tachyarrhythmia), shortness of breath, chest pain, and mild manic symptoms (e.g. excessive speech, irritable mood) after two weeks of taking horny goat weed [54].

Drug Interactions

Horny goat weed may interact with a number of over-the-counter and prescription medications. Talk to your doctor before supplementing if you take any medication on a regular basis.

Cytochrome P450 substrates

Extended use of horny goat weed can increase the production of CYP3A4. Thus, it may reduce the effects of many drugs that are broken down by this group of enzymes [55].

Aromatase Inhibitors

Icariin increases the activity of aromatase, an enzyme involved in estrogen production. This can reduce the effect of aromatase inhibitors (e.g. anastrozole, exemestane, and letrozole) [10].

Blood-Pressure-Lowering Drugs

Horny goat weed may decrease blood pressure. Its combination with medications for high blood pressure might cause your blood pressure to drop too low [1].

Supplementation & Dosing

Horny Goat Weed is generally sold at a higher potency as an extract in liquid or pill form. Supplements can be standardized to their icariin content, which widely ranges between 3% and 20% [2].

A lot of brands combine it with other libido-enhancing herbs, maca being the most common one. Others combine it with tribulus, herbal adaptogens, or with saw palmetto (used to prevent or improve prostate enlargement).

Although unpleasant to the taste, the raw leaves can also be chewed or brewed as a tea. Some manufacturers sell powder from the dried herb in bulk. However, the icariin content in the crude plant is low and its bioavailability poor [2].

Dosage

The dose for horny goat weed has not been established due to the lack of clinical research. Commercially-available supplements contain 600 – 1,000 mg of the extract per tablet or capsule and recommend taking it once daily. Pay attention to the icariin content in standardized extracts, as higher levels of this active compound may point to better-quality, more potent products.

As always, dosing depends on many factors such as age, gender, and health status. However, there is currently not enough scientific information to determine an appropriate range of doses for horny goat weed. With this in mind, it’s wise to avoid high doses and long-term use. If you have any chronic health concerns or take prescription drugs, talk to your healthcare provider before supplementing.

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Takeaway

Horny goat weed (Epimedium) is a herb that has been used in Traditional Chinese Medicine for 2000 years for enhancing sexual desire. In the Western world, it’s especially popular as a male sexual enhancer. Indeed, this herb does have a similar mechanism of action to Viagra, but this has never been confirmed in proper clinical trials.

Due to its flavonoid components, particularly its active ingredient icariin, horny goat weed may have a wide variety of benefits including increasing libido, balancing hormones, boosting energy and cognition, relieving stress, and increasing bone density.

But despite its widespread use, little is known about its actual effectiveness or safety. More clinical trials are needed before its effectiveness is determined.

Horny goat weed is not safe for everyone. People should avoid this herb if they have hormone-sensitive cancer, heart disease, a known allergy to Epimedium, a bleeding disorder, are pregnant or are taking drugs such as aromatase inhibitors and blood-pressure-lowering medications.

Additionally, horny goat weed is not regulated by the FDA and has the potential for contamination. Exercise caution, always read labels and check the manufacturer’s quality standards before buying this supplement.

About the Author

Randa Laouar

BS (Biochemistry & Physiology)

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