The Men’s Performance Supplement Guide

Written for somebody standing in front of a shelf, or a search results page, trying to work out which of forty near-identical bottles is worth anything.

The amino acids: arginine and citrulline

These are the mechanism half of the category, and they are the most straightforward ingredients in it.

L-arginine

An amino acid that the body converts to nitric oxide, which relaxes the smooth muscle in a blood vessel wall and therefore widens the vessel. A 2019 meta-analysis of ten randomised trials in 540 men found arginine supplements significantly better than placebo for erectile function, at daily doses between 1,500 and 5,000 mg, with an adverse event rate of 8.3 per cent against 2.3 per cent on placebo and nothing severe.

That result comes with a hard edge: an earlier controlled crossover study gave 500 mg three times daily and found no benefit at all. The two studies are not in conflict. They describe a dose-response, and the dose is the variable that decides.

L-citrulline

Converted to arginine in the kidneys, with better oral bioavailability than arginine itself, which is why it appears in newer formulations. It is not on every label in this category, and it is worth checking for.

The traditional tonics: horny goat weed, maca and tribulus

Horny goat weed, Epimedium

Its active compound, icariin, inhibits phosphodiesterase-5 in laboratory work, which is the same enzyme family that prescription erectile-dysfunction drugs act on. That is why the plant is in almost every product in this category.

The human evidence is the problem. A thorough review of the genus is largely laboratory and animal work. A randomised, double-blind, placebo-controlled trial of Epimedium prenylflavonoids measured blood levels and found them very low or undetectable at every dose tested. A compound that does not reach the bloodstream in measurable quantity cannot act on an enzyme in a vessel wall.

Maca, Lepidium meyenii

A randomised trial in healthy adult men found improved self-rated sexual desire at 1,500 and 3,000 mg daily after eight weeks, with no change in serum testosterone. That is a genuinely interesting result because it separates desire from hormones. The systematic review pooling four trials is cautious about the small literature, and rightly so.

Tribulus terrestris

The clearest negative in this guide. A 2014 systematic review concluded that tribulus is ineffective for raising testosterone in humans and that marketing claims for it are unsubstantiated. A 2025 systematic review of clinical trials in men found low-level evidence on erectile function and no robust evidence for testosterone. The full text is open access.

It remains in almost every product in this category, which tells you something about how formulation decisions get made.

What actually moves this outcome more than any supplement

A guide that finished at the table above would be dishonest by omission. Four things move energy, stamina and libido more reliably than anything in this guide, and three of them cost nothing.

1. Sleep The largest single lever, and the one most reliably ignored. Testosterone production is concentrated in sleep, and a week of short nights does more than a month of any botanical.
2. Alcohol Acute and chronic effects, both unhelpful, both dose-dependent, both reversible.
3. Activity and body composition Regular resistance and cardiovascular exercise affects both vascular function and hormonal profile, and neither is a marginal effect.
4. A medication review Several common prescription medicines are a documented cause of erectile difficulty, including some antidepressants and blood pressure drugs. A pharmacist will check this for nothing, and a change there can do what no supplement will.