Do male enhancement pills work? The evidence, by ingredient

Do male enhancement pills work? The honest answer depends on what is in them, so this guide checks each common ingredient against the research. Turn over a bottle of almost any male-enhancement supplement and you will find the same dozen or so plants and amino acids, usually in a "proprietary blend". The marketing implies each one has been proven. Some have a handful of small trials behind them. Most have almost nothing in people. One of the most common is a genuine safety risk.

This guide goes ingredient by ingredient through what is claimed, the best evidence we could find (systematic reviews and controlled trials first, NIH fact sheets for safety) and what can go wrong. It is not a recommendation to take any of them. Erectile dysfunction can be an early sign of heart disease or diabetes, and the treatments that reliably work need a prescription: start with our guide to ED treatments that work.

First, how to read the evidence

Three things to keep in mind as you read the rest of this page.

• "Clinically studied ingredient" is not "clinically studied product". A blend that contains ginseng can borrow ginseng's studies without ever being tested itself, and usually at a different dose.
• Small, short and self-reported. Most trials in this field have a few dozen men, last one to three months and measure questionnaire scores. Placebo responses in sexual-function trials are large, so an uncontrolled study that shows improvement tells you very little.
• Mild ED is not all ED. When an ingredient shows any benefit, it is almost always in men with mild to moderate ED. Nothing on this list has been shown to help severe ED, or ED caused by diabetes or prostate surgery, the way prescription treatments do.

Amino acids: L-arginine and L-citrulline

L-arginine

The claim: your body turns arginine into nitric oxide, the molecule that relaxes blood vessels in the penis, so more arginine should mean better erections.

The evidence: this is one of the better-studied ingredients, which is a low bar. A 2019 meta-analysis in the Journal of Sexual Medicine pooled 10 randomized trials with 540 men with mild to moderate ED and found arginine (1.5 to 5 grams a day, alone or in combinations) improved erectile scores compared with placebo. Side effects were more common than on placebo (8.3% vs 2.3%), none severe. The trials were small and varied in dose and length, and several tested arginine combined with other ingredients such as pycnogenol.

Safety: the warning that matters is for heart patients. In the VINTAGE MI trial, people given arginine after a heart attack had 6 deaths in the arginine group and none on placebo, and the safety committee stopped enrollment; the authors concluded arginine should not be recommended after a heart attack. Arginine can also lower blood pressure, which matters if you take blood-pressure drugs or nitrates. Many supplements use doses far below the grams used in trials.

L-citrulline

The claim: the body converts citrulline into arginine more efficiently than it absorbs arginine itself.

The evidence: the study usually cited is a single-blind Italian trial of 24 men with mild ED: 12 of 24 reported normal hardness on citrulline (1.5 g a day) versus 2 of 24 on placebo. It was tiny, short and not double-blind, and the authors themselves said it was less effective than PDE5 inhibitors. Promising, not proof.

Ginseng

The claim: Korean red ginseng (Panax ginseng) is a traditional tonic for stamina and sexual function and appears in most blends.

The evidence: a 2021 Cochrane review found nine trials with 587 men with mild to moderate ED, all against placebo and none longer than 12 weeks. Its conclusion: ginseng appears to have only a trivial effect on erectile function scores, below the change men would notice, though it may improve self-reported ability to have intercourse; the certainty of evidence was mostly low. NCCIH's Asian ginseng fact sheet says it seems to improve sexual function in some research and warns it might interact with certain medications.

Verdict: the best-studied herb in these blends, and still a modest effect at best, at doses many blends don't disclose.

Horny goat weed (epimedium, icariin)

The claim: icariin, a compound in epimedium, works a little like sildenafil by inhibiting the PDE5 enzyme.

The evidence: that mechanism comes from lab and animal studies. Memorial Sloan Kettering's integrative medicine database notes it is traditionally used for sexual dysfunction but cites no controlled human trials for it. It reports side effects including rapid or irregular heartbeat, heavy sweating and mood changes, a case of a man with heart failure who developed an irregular heartbeat and hypomania after two weeks of use, estrogen-like effects, and advises people with heart disease to avoid it. Toxicity and safety data are lacking.

Is yohimbe safe? The one to avoid

The claim: yohimbe bark from a West African tree is an aphrodisiac and erection aid.

The evidence: yohimbine, the bark's main alkaloid, is the only ingredient here that was once a prescription drug for ED, and an older meta-analysis of seven placebo-controlled trials (1998) found it beat placebo. That was before PDE5 inhibitors, and it is not what supplements contain: NCCIH says yohimbe sold as a dietary supplement may not work like the prescription medication and that there isn't enough research to say whether it helps any condition, ED included.

Safety: this is the real problem. NCCIH lists yohimbine's links to irregular heartbeat, high blood pressure, heart attacks and seizures, plus anxiety and a racing heart, and warns against combining it with MAOI or tricyclic antidepressants. Doses are also unpredictable. When Harvard researcher Pieter Cohen and colleagues tested 49 US supplements labeled as yohimbe, yohimbine per serving ranged from none to 12.1 mg, only 11 brands stated an amount, most of those labels were wrong (23% to 147% of the stated dose), and some products appeared to contain synthetic yohimbine. If a label lists yohimbe, skip it, and especially if you have any heart condition, high blood pressure or anxiety.

Tribulus terrestris

The claim: raises testosterone and libido.

The evidence: mixed and weak. A Brazilian randomized, double-blind trial in men over 40 with ED found tribulus was no better than placebo for erections or testosterone after 30 days. A 2019 Egyptian placebo-controlled trial in 70 older men with low testosterone reported improvements in erectile scores and testosterone, along with small rises in a liver enzyme and PSA. Different populations, small numbers, conflicting results: that is not a foundation for a product claim. Our testosterone boosters guide covers the hormone side.

Maca

The claim: a Peruvian root that boosts libido and stamina.

The evidence: a 2010 systematic review found only four small randomized trials and concluded they provide limited evidence, with too few trials and too few participants to draw firm conclusions. Maca is a food plant and is generally regarded as low risk, but "low risk" and "works" are different claims.

Ginkgo biloba

The claim: improves blood flow, including to the penis, and reverses sexual side effects of antidepressants.

The evidence: the antidepressant idea came from an uncontrolled report in the late 1990s. When it was tested properly, a placebo-controlled, double-blind trial found no significant difference from placebo, with both groups improving, which the authors read as a placebo effect. NCCIH's ginkgo fact sheet warns it may increase bleeding risk in people taking anticoagulants such as warfarin and may interact with other drugs.

Saw palmetto

Saw palmetto is a prostate supplement, sold for urinary symptoms of an enlarged prostate. It is in several enhancement blends anyway. NCCIH's saw palmetto fact sheet reports that the large NIH-funded trials found it did not improve urinary symptoms more than placebo. There is no good evidence it improves erections.

Zinc

Severe zinc deficiency can impair testosterone production, which is where the claim comes from. The NIH Office of Dietary Supplements' zinc fact sheet lists hypogonadism among the signs of deficiency, and sets the tolerable upper intake for adults at 40 mg a day; chronic high doses can cause copper deficiency. Most men in the US get enough zinc from food, and topping up a normal level has not been shown to improve erections.

DHEA

DHEA is a hormone precursor the body converts into testosterone and estrogen. One frequently cited Austrian trial of 40 men reported better erectile scores on DHEA, with the authors noting their patient database was too small for relevant statistical analysis. It is a hormone, sold over the counter, with the possibility of hormonal side effects, and it is on anti-doping banned lists. If you think your hormones are the problem, get them tested rather than guessing.

Fenugreek, tongkat ali and the rest of the blend

Fenugreek is sold for libido and testosterone, mostly on the strength of small, often manufacturer-funded trials of particular extracts. NCCIH's fenugreek fact sheet notes digestive side effects and that large doses may cause a harmful drop in blood sugar, worth knowing for anyone on diabetes medicine. Tongkat ali (Eurycoma longifolia) is covered in our testosterone guide.

Muira puama, catuaba, damiana, hawthorn, cuscuta, bioperine and similar names round out many labels. We found no controlled human trials showing any of them improves erections on its own. Bioperine is a black-pepper extract added to increase absorption of the other ingredients, which also means it can increase absorption of your other medicines.

How to read a male enhancement supplement label

Proprietary blends hide the doses

US labeling rules let a company list a proprietary blend by its total weight, with ingredients in descending order of weight but without the amount of each. A 500 mg blend of twelve herbs might contain a few milligrams of the ones with any evidence. If the label won't tell you the dose, you can't compare it with the trials.

The disclaimer is the tell

Supplements can make structure/function claims ("supports male vitality") but not claims to treat a disease, and must say the FDA has not evaluated them. A product that promises to cure ED, or works like a prescription drug within the hour, deserves the suspicion our tainted supplements guide explains.

Questions to ask before buying

• Is the dose of each ingredient listed?
• Has the product itself (not its ingredients) been tested in a published, placebo-controlled trial, and who paid for it?
• Does it contain yohimbe, DHEA or anything hormonal?
• Do any ingredients interact with what you already take? Ask your pharmacist.
• What exactly does the money-back guarantee require, and is there an autoship subscription?

Does L-arginine work for erectile dysfunction?

There is some evidence for mild to moderate ED: a 2019 meta-analysis of 10 small trials found arginine beat placebo at 1.5 to 5 grams a day. The trials were small and varied, many blends contain far less, and it is not recommended for people who have had a heart attack.

Does horny goat weed work?

Not that anyone has shown in people. The idea that its compound icariin acts like sildenafil comes from lab and animal studies, and Memorial Sloan Kettering lists heart-rhythm side effects and advises people with heart disease to avoid it.

Are natural male enhancement pills safe?

"Natural" is not a safety label. Yohimbe can raise blood pressure and heart rate, ginkgo can increase bleeding risk with blood thinners, DHEA is a hormone, and some products sold as natural contain hidden prescription drugs.

We apply this ingredient by ingredient to each product in the male enhancement pill comparison, including Semenax and Volume Pills.

What are the best male enhancement pills?

If you want a herbal blend anyway, the ingredients with the least-bad evidence for mild ED are arginine and ginseng, at the doses used in trials, which many blends don't reach. Yohimbe is the one to avoid. Everything else is mostly tradition and marketing. Our reviews of VigRX Plus, Erectin and Extenze apply this to each product's actual label. And if ED is a pattern rather than a bad night, see a doctor first: the treatments that work are cheaper than most of these bottles.