For mild erectile dysfunction, a few ingredients have genuine but small trials: L-citrulline 1.5 g/day improved erection hardness in half of men versus 8% on placebo in a one-month single-blind study; L-arginine at 1.5–5 g/day shows modest benefit in meta-analyses of small trials; Panax ginseng and tongkat ali show weak positive signals. Effects are far below prescription PDE5 inhibitors. The category's dark side is real: regulators repeatedly find "natural" ED products spiked with undeclared sildenafil analogues. And because new ED is an early cardiovascular warning, the first move is a check of blood pressure, glucose and lipids — not a capsule that postpones it.
The two-part honest answer
Part one: a few ingredients have real, small trials in mild ED, mostly working through the nitric-oxide pathway that erections run on. Part two: the category is the most adulterated in the supplement market, and its marketing encourages men to skip the medical assessment that new ED should trigger — because ED is often the first sign of vascular disease, diabetes or low testosterone. Any use of supplements belongs after that check, not instead of it.
What the trials show
| Ingredient | Verdict | What trials show |
|---|---|---|
| L-citrulline | Limited | In a single-blind crossover trial, 1.5 g/day for a month moved erection hardness from "not enough for penetration" to "sufficient" in 50% of men with mild ED versus 8% on placebo. Small (24 men), short, single-blind — but a real signal on the right mechanism. |
| L-arginine | Limited | Meta-analyses of small trials at 1.5–5 g/day show modest improvements in mild-to-moderate ED versus placebo; high doses cause stomach upset, and effects are inconsistent. |
| Panax ginseng ("red ginseng") | Limited | Several small trials and meta-analyses suggest improvement over placebo; a Cochrane review judged the evidence low-certainty with trivial-to-small effects. |
| Tongkat ali | Insufficient | A meta-analysis of two randomized trials found no significant improvement in erectile-function scores overall; any benefit is likelier in men whose issue is low testosterone. |
| Horny goat weed | Insufficient | Mechanistically plausible (icariin weakly inhibits PDE5) but no adequate human trials. |
| Yohimbine | Mixed, poor safety | Older trials show benefit over placebo, but anxiety, palpitations and blood-pressure effects make it a poor over-the-counter choice; some countries restrict it. |
| Maca | Insufficient for ED | Small trials suggest desire effects more than erectile ones. |
| Zinc, vitamin D | Deficiency-dependent | Correcting a genuine deficiency helps the hormonal side; supplementing sufficiency does not treat ED. |
For scale: PDE5 inhibitors restore satisfactory erections in roughly 70% of men across causes. Nothing on this table is in that conversation.
The adulteration problem
Regulators in the US, UK, Canada and Australia repeatedly find sexual-enhancement supplements containing undeclared sildenafil, tadalafil or untested analogues — hundreds of products over the years, often labelled "100% natural". The danger is concentrated in men taking nitrates for heart disease, where hidden PDE5 drugs can cause severe hypotension; the irony is that the buyers most drawn to "natural" alternatives are often exactly the men with the heart conditions that make hidden drugs dangerous. Practical defence: single-ingredient products from brands with third-party testing (USP, NSF, Informed Choice), and deep suspicion of anything promising fast results.
What works better than any of this
Trials of aerobic exercise show erectile-score improvements comparable to the lower range of drug effects; weight loss in men with obesity improves erections and testosterone together; stopping smoking, moderating alcohol, treating sleep apnea, and reviewing culprit medications each move the needle. And the prescription options — PDE5 inhibitors first line — are effective, well understood and now inexpensive as generics. The full picture, including when ED signals something urgent, is in the erectile dysfunction guide.
If you still want to trial a supplement
Reasonable, once a doctor has ruled out the things ED can announce and okayed it alongside your medications: L-citrulline 1.5–3 g/day for 4–8 weeks is the pick on evidence and safety, with ginseng the second choice. Buy tested single ingredients, keep notes, and stop what does not help. Our men's health product research covers the commercial blends — and names which ones ride on the ingredients above at doses they decline to print.
Frequently asked questions
Is L-citrulline better than L-arginine?
Milligram for milligram, citrulline raises blood arginine more efficiently, because swallowed arginine is largely broken down before it circulates while citrulline escapes that and is converted to arginine in the kidneys. The clinical trials of each are small; citrulline's dosing (1.5–3 g/day) is more practical than the 3–5 g of arginine used in studies.
How would I know if a "herbal" ED product is spiked?
You usually can't — that is the problem. Warning signs: effects that feel drug-like within an hour, products marketed for use "30 minutes before activity", and any brand that has appeared in FDA or other regulator recall lists. Spiked products endanger men on nitrates, for whom hidden sildenafil can cause dangerous blood-pressure drops.
Can I take citrulline with sildenafil or tadalafil?
Small studies have combined citrulline with PDE5 inhibitors without safety signals, and both act on the same nitric-oxide pathway. Because the combination can add blood-pressure effects, and because ED treatment should be medically supervised anyway, run it past the prescriber.
What about horny goat weed, yohimbine, maca?
Horny goat weed contains a weak PDE5-inhibiting compound (icariin) with animal data and no good human trials. Yohimbine has older trial evidence but a poor side-effect profile (anxiety, blood pressure, palpitations) and is best avoided outside medical use. Maca shows libido effects in small trials more than erectile ones.
References
- Urology. Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction (2011). PubMed PMID 21195829. https://pubmed.ncbi.nlm.nih.gov/21195829/
- Complementary Therapies in Medicine. Efficacy of Tongkat Ali (Eurycoma longifolia) on erectile function improvement: systematic review and meta-analysis of randomized controlled trials (2015). PubMed PMID 26365449. https://pubmed.ncbi.nlm.nih.gov/26365449/
- NIDDK. Erectile Dysfunction (ED) (2024). https://www.niddk.nih.gov/health-information/urologic-diseases/erectile-dysfunction
- U.S. Food and Drug Administration. Dietary Supplements (2024). https://www.fda.gov/food/dietary-supplements
This page discusses supplement ingredients or categories. It may mention a commercial product, with disclosure. It is general health information, not personal medical advice. Read our editorial policy and medical review policy.