L-Arginine

What is L-arginine?

L-arginine is a semi-essential amino acid found in protein foods such as meat, poultry, fish, dairy, nuts and legumes. The body also makes it from another amino acid, citrulline. Arginine is the substrate for nitric oxide synthase, the enzyme that produces nitric oxide in blood vessel walls. Nitric oxide relaxes smooth muscle and widens blood vessels, which is why arginine is a common ingredient in circulation, workout and male performance supplements.

What the research says

Erectile function

A 2019 systematic review and meta-analysis pooled 10 randomized trials with 540 men with mild to moderate erectile dysfunction. Arginine at 1,500 to 5,000 mg a day significantly improved erectile function compared with placebo or no treatment, along with satisfaction and orgasmic function scores, while sexual desire did not change. Adverse effects occurred in 8.3% of men taking arginine versus 2.3% on placebo, none serious. The authors noted that doses and treatment lengths varied, adding uncertainty (Rhim et al., 2019). Several included trials combined arginine with other compounds, so the effect of arginine alone is less clear.

Absorption

Much of an oral arginine dose is broken down in the gut and liver before reaching the circulation. In a crossover pharmacology study, oral L-citrulline raised blood arginine more effectively than the same amount of L-arginine (Schwedhelm et al., 2008). That is one reason many formulas pair the two, or favor citrulline.

Heart attack caution

The most important safety finding comes from the VINTAGE MI trial. People recovering from a heart attack took L-arginine (goal dose 3 grams three times a day) or placebo for six months. Arginine did not improve blood vessel stiffness or heart function, and 6 people in the arginine group died versus none on placebo, so enrollment was stopped. The authors concluded arginine should not be recommended after a heart attack (Schulman et al., 2006).

Context from supplement reviews

A 2023 review of marketed sexual-health supplements found arginine was among the few ingredients with some supportive evidence, but that many products used it at doses too low to matter (Petre et al., 2023).

How it’s used in supplements

Arginine is sold as capsules, tablets and powders, often as L-arginine hydrochloride or arginine alpha-ketoglutarate. Effective doses in trials are in the gram range, which usually requires several capsules or a scoop of powder. Common side effects are stomach upset, bloating and diarrhea. Because it can lower blood pressure, it may add to the effects of blood pressure medicines, nitrates and erectile drugs. People with heart disease, especially after a heart attack, people with low blood pressure or kidney disease, and those who are pregnant or breastfeeding should not use arginine without medical advice.