L-arginine: what it does, what the evidence says on blood pressure and erections, and who should avoid it

What L-arginine is

L-arginine is an amino acid your body can make, and you also get it from protein foods. Denmark’s National Food Institute (DTU) estimates that people get about 3–5 g of arginine a day from an ordinary diet. Meat, fish, dairy, nuts and seeds are all good sources.

The main reason for interest in arginine is nitric oxide (NO). An enzyme called nitric oxide synthase makes NO from arginine, and NO relaxes the muscle in blood vessel walls. Vessels widen, blood pressure drops slightly and blood flow improves. That’s where the hopes for arginine in high blood pressure, angina and erectile dysfunction come from.

Arginine is also used to build proteins and creatine: your body makes creatine from glycine, arginine and methionine.

L-arginine benefits: what the evidence says

Mayo Clinic rates arginine as generally safe and possibly helpful for high blood pressure, angina, peripheral artery disease (leg pain on walking due to poor blood flow) and erectile dysfunction with a physical cause. It also says arginine isn’t recommended for anyone who has recently had a heart attack.

So the benefits are modest and the risks for some groups are serious. This isn’t a supplement to take “just in case”.

L-arginine and blood pressure

A 2011 meta-analysis pooled 11 double-blind, placebo-controlled trials with 387 people. Doses ranged from 4 to 24 g a day. Compared with placebo, systolic pressure fell by 5.4 mmHg on average and diastolic by 2.7 mmHg. The result held when only trials of 4 weeks or longer, and only people not on blood pressure medicines, were counted.

That’s a modest effect. It doesn’t replace blood pressure tablets your GP has prescribed. If you already take them, arginine may add to their effect and push your blood pressure too low.

L-arginine for men: the evidence on erections

A 2019 meta-analysis gathered 10 trials with 540 men with mild to moderate erectile dysfunction. Arginine at 1.5–5 g improved erections more often than placebo or no treatment. Side effects affected 8.3% of men on arginine and 2.3% on placebo, and none were severe.

These data have real limits:

• some trials gave arginine together with other ingredients, so arginine’s own share is unclear;
• doses and durations varied a lot;
• severe ED wasn’t studied.

Erections depend on healthy blood vessels, so ED is often linked with high blood pressure, diabetes and high cholesterol. If you have problems, see your GP first and get these checked. Don’t combine arginine with sildenafil without medical advice, as your blood pressure could drop too far. There’s no promise of better sexual performance here. For what usually makes sense for men, see our guide to supplements for men and the men’s health and sport section.

L-arginine after a heart attack: the VINTAGE MI trial

This is the biggest reason for caution. The VINTAGE MI trial (2006) enrolled 153 people after a first heart attack. Average age was 60, and 68% were men. Half took arginine, aiming for 9 g a day, and half took a placebo for 6 months on top of usual treatment.

• Arginine didn’t improve artery stiffness or heart function.
• 6 people (8.6%) died in the arginine group and none in the placebo group.
• The safety committee stopped recruitment early.

Death wasn’t the trial’s main outcome, so chance can’t be ruled out. But the authors stated plainly that arginine should not be recommended after an acute heart attack. Mayo Clinic gives the same advice.

L-arginine and herpes

People with herpes are often told to be careful with arginine. In cell culture studies from 1981, the herpes simplex virus needed arginine to multiply, and lysine, a similar amino acid, held it back. That’s the basis of the common advice to limit arginine-rich foods such as nuts and seeds.

Whether this matters in people isn’t known, because good trials are lacking. But if you get frequent cold sores or genital herpes flare-ups, discuss large doses of arginine with your GP first.

L-arginine side effects

At usual doses, healthy adults tolerate arginine fairly well. Mayo Clinic lists these possible effects when it’s taken by mouth:

• nausea, stomach pain, bloating and diarrhoea;
• headache;
• gout flare-ups;
• allergic reactions, airway inflammation and worsening asthma.

How does that compare with food? DTU estimates that 6 g of arginine from a supplement roughly doubles what you’d get from an ordinary diet. Total intake still stays well below 20 g a day, the level up to which no harm was found in healthy adults. Human studies have used up to 42 g a day for up to several months, but they weren’t designed to test safety, and you don’t need doses like that.

L-arginine interactions with medicines

According to Mayo Clinic, arginine may interact with:

• nitrates such as GTN (glyceryl trinitrate) for angina: blood pressure may drop too far;
• sildenafil: also a risk of very low blood pressure;
• blood pressure medicines: the effects add up;
• potassium-sparing diuretics (spironolactone, amiloride, triamterene): blood potassium may rise to unsafe levels;
• blood thinners: a possible higher risk of bleeding;
• diabetes medicines: blood sugar may fall further.

If you carry a GTN spray for angina, arginine isn’t for you unless your GP says otherwise. To check supplement combinations, use our vitamin compatibility chart.

L-arginine dosage: how to take it

1. Do the safety check above. If any line doesn’t apply to you, see your GP first.
2. Start with the dose on the label. Check the grams of arginine per serving rather than the capsule weight.
3. Use the trials as a guide: 1.5–5 g a day for erectile function, 4–24 g for blood pressure.
4. Stay under 20 g a day. Safety in healthy adults is supported up to that level; DTU judged 6 g a day from a supplement to be safe.
5. Watch how you feel. Nausea, stomach pain, bloating or diarrhoea mean lowering the dose. Check your blood pressure at home.
6. Review after 4–8 weeks. No effect means no point carrying on.

Who should avoid L-arginine without medical advice

• Anyone who has had a heart attack, or has angina or heart failure.
• Anyone taking nitrates, sildenafil, blood pressure medicines, potassium-sparing diuretics, blood thinners or diabetes medicines.
• People with frequent herpes outbreaks.
• People with asthma or severe allergies.
• Pregnant or breastfeeding women, and children: a doctor should decide.

How to choose L-arginine on iHerb

1. Look for L-arginine and find the line with the grams of arginine per serving.
2. For doses of several grams, powder is more practical than capsules.
3. Compare the price per 1 g of arginine in £ or €, not per tub.
4. Skip “men’s blends” with ten herbs: you can’t tell what works or what it interacts with.
5. Not sure you need a supplement? Try our vitamin check.

Our Supplement Facts guide explains how to find the grams on a label and work out the cost per dose. Another amino acid popular with men and athletes is L-carnitine.