L-arginine is an amino acid found in meat, fish, dairy, nuts and pulses, and the body can also make it. Its role in sexual health comes from nitric oxide: the enzyme that produces nitric oxide in blood vessel linings and penile nerves uses L-arginine as its raw material. Nitric oxide relaxes the smooth muscle in the penis so blood can flow in, which is the same pathway PDE5 inhibitors such as sildenafil enhance further down the chain.
A 2019 meta-analysis of 10 randomised trials involving 540 men with mild to moderate erectile dysfunction found that arginine supplements improved erectile function compared with placebo or no treatment, along with scores for intercourse satisfaction, orgasmic function and overall satisfaction. Trials used between 1,500 and 5,000 mg a day, and side effects were more common with arginine (8.3% versus 2.3%), though none were severe.1
A 2024 network meta-analysis of 15 trials in 1,000 men with erectile dysfunction, which ranked many supplements and medicines against each other, found L-arginine had a statistically significant effect on erectile function scores compared with placebo. L-arginine combined with tadalafil ranked second of all the regimens studied, with the clearest benefit in men with physical causes of ED.2
Why is L-arginine in semen volume supplements?
L-arginine is a common ingredient in semen volume supplements, where it is included for its role in blood flow and erections. Its research has focused on erectile function rather than the amount of fluid ejaculated.
The trials recruited men who already had erection problems, mostly mild to moderate, and measured erectile function with questionnaires.1 Semen volume itself depends mostly on the seminal vesicles, prostate and time since last ejaculation, and has not been a main outcome in L-arginine studies.
If erections have changed, a check-up is worthwhile alongside anything you try yourself, because erection problems can share causes with heart and blood vessel disease.
Why is L-citrulline sometimes preferred?
Much of an oral L-arginine dose is broken down in the gut and liver before it reaches the bloodstream. L-citrulline is absorbed more readily and converted into arginine in the body.
In a crossover study of 20 healthy volunteers, oral L-citrulline raised blood arginine levels more effectively than L-arginine itself, and increased markers of nitric oxide signalling.3 The two have not yet been compared head to head for erections in large trials, and research on products that combine them is ongoing.
Is L-arginine safe?
Most men in ED trials tolerated it, with mild side effects such as stomach upset. It is not suitable for everyone, particularly people with heart disease.
A trial giving L-arginine to people after a heart attack was stopped early: six people (8.6%) taking arginine died during the six-month study compared with none on placebo, and the authors concluded it should not be recommended after a heart attack.4
Because L-arginine acts on blood vessels, talk to a doctor before using it if you have heart disease, low blood pressure, or take nitrates, blood pressure medicines or PDE5 inhibitors. It is also worth seeing a doctor about erectile dysfunction rather than only self-treating.
Common questions
Does L-arginine work like Viagra?
It acts on the same nitric oxide pathway, but in a different way: it supplies the raw material for nitric oxide, while PDE5 inhibitor medicines block the enzyme that ends an erection. Trials in men with mild to moderate ED found improved erectile function scores, and it has been studied alongside tadalafil as well as on its own.12
How long did L-arginine trials last?
Trials generally ran for several weeks, so any effect is likely to build gradually rather than work on demand. Doses varied between trials, from 1,500 to 5,000 mg a day.1
Can I take L-arginine with sildenafil or tadalafil?
Some trials combined them,2 but both affect blood vessels and blood pressure. Ask your doctor before combining them, especially if you have any heart condition.
Read more on this
Supplement ingredients for men’s sexual health: what the research shows
Does cardio really improve erections? What the research says
Sources
- Rhim HC, et al. The potential role of arginine supplements on erectile dysfunction: a systemic review and meta-analysis. J Sex Med. 2019;16(2):223-234. PubMed
- Barbonetti A, et al. Nutraceutical interventions for erectile dysfunction: a systematic review and network meta-analysis. J Sex Med. 2024;21(11):1054-1063. PubMed
- Schwedhelm E, et al. Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism. Br J Clin Pharmacol. 2008;65(1):51-9. PubMed
- Schulman SP, et al. L-arginine therapy in acute myocardial infarction: the Vascular Interaction With Age in Myocardial Infarction (VINTAGE MI) randomized clinical trial. JAMA. 2006;295(1):58-64. PubMed
Not medical advice. Written by Eric Stephens from the research cited above; not reviewed by a doctor. If something worries you, see a GP.