L-Arginine: Benefits for Men, Dosage and Side Effects

Nitric oxide synthase converts L-arginine to nitric oxide, which relaxes vascular smooth muscle and widens blood vessels. The practical catch is first-pass metabolism: much of an oral dose is broken down by arginase in the gut and liver before it reaches circulation, which is why oral doses have to be large and why L-citrulline (which converts to arginine downstream) often outperforms it gram for gram.

• Erectile function: a 2019 meta-analysis found doses of 1,500-5,000 mg improved erectile function scores against placebo, with larger effects in men with measurable vascular dysfunction.
• Blood pressure: a dose-response meta-analysis of randomised trials found reductions in systolic and diastolic pressure, at doses of 4-24 g/day (median 9 g/day).
• Combination use: trials pairing arginine with a PDE5 inhibitor showed better results than the inhibitor alone, though the inhibitor alone still beat arginine alone.
• Exercise: the weakest of its uses. Effects on strength and endurance are small and inconsistent.

Rhim 2019 meta-analysis of arginine for erectile dysfunction, and a 2022 dose-response meta-analysis in Advances in Nutrition for blood pressure. The direction of effect is consistent across both; the size is modest. Evidence for ergogenic use is markedly weaker than for vascular use, despite pre-workout marketing leaning on the opposite.

3-6 g/day is the usual supplement range and the one used in most erectile-function trials. Blood-pressure trials generally used more, a median of 9 g/day. Doses are best split across the day because single large doses are what cause the GI problems. Effects on vascular measures build over weeks, not on the first dose.

GI upset is the dose-limiting problem: bloating, cramping and diarrhoea become common above roughly 9 g in a single dose. Some people report nausea. Because it lowers blood pressure it can cause light-headedness when stacked with antihypertensives.

Additive blood-pressure lowering with antihypertensives, nitrates and PDE5 inhibitors such as sildenafil, which can produce symptomatic hypotension. Caution with anticoagulants. Anyone who has had herpes simplex should know that arginine can promote viral replication in laboratory conditions, though clinical relevance is unsettled. People who have had a recent heart attack should avoid supplemental arginine: a Johns Hopkins trial was stopped early over a mortality signal in that group.