Research review
Does L-citrulline raise testosterone? What the research does and doesn't show
L-citrulline hasn't been shown to raise testosterone — the one trial that measured it directly, in young male athletes, found no significant change. A separate small trial found improved erection hardness in men with mild erectile dysfunction, a different outcome tied to citrulline's nitric-oxide pathway rather than a hormonal effect.
The evidence doesn't support L-citrulline as a way to raise testosterone — the one trial that measured it directly found no change. What's actually been tested and found positive is narrower and different: improved erection hardness in men with mild erectile difficulty in one small trial, on the strength of citrulline's role in the nitric-oxide pathway rather than any hormonal effect.
What the evidence doesn't support
It doesn't support L-citrulline as a testosterone booster — the only trial below that measured resting testosterone directly found no significant change, in either direction. It doesn't support L-citrulline as a treatment for erectile dysfunction as a diagnosed condition, or as a replacement for prescription treatment — the one positive trial's own authors describe citrulline as less effective than standard PDE-5 inhibitor medication and suggest it only as an option for men reluctant to use that medication, not instead of seeing a doctor. And it doesn't support a libido or sexual-performance effect in men without an existing erectile difficulty — no trial below tested that population.
What the trials found
A 2025 randomized, controlled trial gave 40 young male basketball players (mean age 21.5) either L-citrulline (6 g/day), sodium bicarbonate, both combined, a placebo, or an untrained active-control condition, alongside 4 weeks of sprint-interval training. Every supplemented group improved physical-performance measures more than placebo. Resting testosterone did not change significantly in any group, including the citrulline-only group; the supplemented groups did show lower cortisol, a stress hormone, than the other groups after the intervention. This is the most direct human test of citrulline and testosterone we found, and it's a null result on that specific outcome.
A 2011 single-blind, sequential trial gave 24 men (mean age 56.5) with mild erectile dysfunction — an erection-hardness score of 3 out of 4 — a placebo for one month and 1.5 g/day of L-citrulline for a second month. The erection-hardness score improved from 3 to 4 (normal function) in 50% of the men during the citrulline month, compared with 8.3% during the placebo month (p<0.01), and monthly intercourse frequency rose from about 1.4 to 2.3. No adverse events were reported. The trial didn't measure testosterone — its outcome was erection hardness and intercourse frequency, not a hormone level — and its own authors describe citrulline as less effective than PDE-5 inhibitor medication, calling it a possible option specifically for men reluctant to take that medication rather than a replacement for it. It's a small, single-blind trial with mild symptoms only, and we didn't find an independent replication.
The mechanism behind both the erectile-function interest and the testosterone marketing is the same: citrulline converts to arginine, which feeds nitric-oxide production, a signaling molecule involved in blood-vessel dilation, including in the tissue involved in an erection. That's a plausible reason to test citrulline for erectile function, which the 2011 trial did with a positive result at a small scale. It isn't, on its own, a reason to expect a testosterone effect — the two are different physiological questions, and the one trial that tested testosterone directly found nothing.
Questions people ask
Does L-citrulline increase testosterone?
The one trial that measured it directly — 6 g/day for 4 weeks in young male athletes — found no significant change in resting testosterone in the citrulline group.
Does L-citrulline increase libido?
No trial below measured libido as its own outcome. The 2011 trial measured erection hardness and intercourse frequency in men with an existing mild erectile difficulty, which is a related but different question from libido or sexual desire in general.
Does L-citrulline help erectile dysfunction?
One small, single-blind trial found improved erection hardness in men with mild erectile dysfunction on 1.5 g/day for a month — its own authors describe it as less effective than prescription PDE-5 inhibitor medication. It hasn't been tested in men with moderate or severe erectile difficulty, and we didn't find an independent replication of this specific trial.
Is L-citrulline or L-arginine better for erectile dysfunction?
We didn't find a trial comparing the two head-to-head for this specific outcome. The rationale for citrulline over arginine is pharmacokinetic — citrulline mostly escapes the breakdown that limits how much oral arginine reaches circulation — not a result from a direct comparison trial on erectile function.
When to talk to a doctor
L-citrulline is not a treatment for low testosterone or erectile dysfunction as diagnosed conditions, and nothing above should stand in for a doctor's evaluation of either. If erectile difficulty, low libido, or a suspected hormonal issue is ongoing, talk to a doctor rather than self-treating with a supplement — and if you take a PDE-5 inhibitor or nitrate medication, ask a doctor before adding L-citrulline given the shared nitric-oxide mechanism.
Related reading: L-citrulline benefits: what the research does and doesn't show and L-citrulline and medications: what to check.
Sources
- Combined Vs. Single Supplementation of L-Citrulline and Sodium Bicarbonate During Sprint Interval Training in Basketball Players: Effects on Physical Performance and Hormonal Adaptations A 2025 trial in 40 young male basketball players found that 6 g/day of L-citrulline for 4 weeks, alongside sprint-interval training, improved physical performance more than placebo but did not significantly change resting testosterone; cortisol, a stress hormone, was lower in the supplemented groups.
- Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction A 2011 single-blind trial in 24 men with mild erectile dysfunction found that 1.5 g/day of L-citrulline for a month improved erection hardness in half the men, versus about 8% during a placebo month, with no adverse events reported — the study's own authors describe it as less effective than standard PDE-5 inhibitor medication.
- Citrulline: pharmacological perspectives and its role as an emerging biomarker in future A 2013 pharmacology review describes L-citrulline as a naturally occurring amino acid and urea-cycle intermediate that the body converts to arginine more efficiently than arginine converts to itself, and lists the range of conditions where its supplementation is being researched, from erectile dysfunction to rare urea cycle disorders.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.