Last updated: 10 November 2026
L-arginine is an amino acid your body uses to make nitric oxide, a gas that helps blood vessels relax and widen. Most people get about 4 to 5g a day from protein foods such as meat, fish, dairy, nuts, seeds and beans. Supplements are often 500mg a capsule, while trials used 1.5 to 24g a day.
L-arginine is sold for blood pressure, circulation, erections and exercise. Below: what it does, what the trials actually found, whether a 500mg capsule is enough, how it compares with L-citrulline and beetroot, and the medicines it mustn’t be mixed with without advice.
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Magnesium Glycinate Sleep Complex
Evopure doesn’t sell L-arginine. If you want an everyday supplement for energy and muscles, Evopure’s Magnesium Glycinate Sleep Complex is a berry drink powder with 290mg of magnesium (77% NRV) per 4.75g serving, from magnesium bisglycinate and citrate. Magnesium contributes to normal muscle function and to a reduction of tiredness and fatigue.
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View productWhat is L-arginine?
L-arginine is an amino acid, one of the building blocks of protein. Healthy adults make some in the body and get the rest from food, so it is called conditionally essential: needs rise after injury, surgery or serious illness. Its best-known job is making nitric oxide, which relaxes the walls of blood vessels.
| L-arginine fact | The detail |
|---|---|
| Type | Conditionally essential amino acid |
| Main jobs | Makes nitric oxide; also used for protein, creatine and urea |
| Intake from food | About 4.4g a day on average (US national survey) |
| Common capsule | 500mg |
| Amounts in trials | 1.5 to 5g a day (erections); 4 to 24g a day (blood pressure) |
| Safety level | Industry-funded review: no clear harm up to 20g a day in healthy adults |
| GB health claims | None authorised; EFSA rejected blood pressure, circulation and erection claims |
| Never without advice | After a heart attack, or with nitrates, sildenafil or tadalafil |
In the UK, L-arginine is sold as a food supplement. Protein-rich foods supply far more than most capsules do; see how much protein do I need?
What does L-arginine do?
L-arginine is turned into nitric oxide by enzymes in the lining of blood vessels. Nitric oxide signals the muscle in vessel walls to relax, which widens them and lets blood flow more easily. Arginine is also used to make proteins, creatine and urea, which helps the body clear ammonia.
The catch with supplements is absorption. Much of the arginine you swallow is broken down in the gut and liver before it reaches your blood. In a study of 20 healthy volunteers, L-citrulline raised blood arginine more effectively than the same amount of L-arginine itself.
L-arginine benefits: what the research shows
The best evidence for L-arginine is a small fall in blood pressure, about 5 points systolic, in trials using 4 to 24g a day. Trials in men with mild to moderate erection problems also found improvements at 1.5 to 5g a day. These doses are far above a 500mg capsule, and no L-arginine health claim is authorised in Great Britain.
| What was studied | What studies found | How strong |
|---|---|---|
| Blood pressure | 11 trials, 387 people, 4 to 24g a day: systolic down 5.4 mmHg, diastolic down 2.7 mmHg vs placebo | Review, small trials |
| Erection problems | 10 trials, 540 men with mild to moderate erectile dysfunction, 1.5 to 5g a day: better scores than placebo; more side effects (8.3% vs 2.3%) | Review, small trials |
| After a heart attack | 3g three times a day for 6 months: no benefit, and 6 deaths in the arginine group vs none on placebo; trial stopped early | Trial, safety signal |
| Exercise, muscle, immunity | EFSA found the claims unproven or too vague | Claims rejected |
Does L-arginine lower blood pressure?
A little, at high doses. Trials using 4 to 24g a day lowered blood pressure by about 5 points systolic and 3 points diastolic. It is smaller than the effect of most blood pressure medicines and no substitute for them: if you have high blood pressure, see your GP and never stop prescribed treatment. Our guides to normal blood pressure and low blood pressure explain the numbers.
L-arginine and erectile dysfunction
Small trials suggest L-arginine may help some men with mild to moderate erection problems, but no claim is authorised for it. Erection problems can be an early sign of heart disease, diabetes or high blood pressure, so see a GP rather than self-treating. For other evidence-led supplements for men, see supplements for men over 40 and 50.
Is L-arginine 500mg enough?
A 500mg L-arginine capsule is about a ninth of the 4 to 5g most people already get from food each day, and well below the 1.5 to 24g used in trials. On its own, 500mg is unlikely to have a measurable effect on blood pressure or blood flow. Labels usually suggest 1 to 3 capsules a day.
Don’t take several grams a day to match the trials if you have heart disease, low blood pressure or take any of the medicines below without speaking to your GP first. Higher doses also bring more stomach upset and diarrhoea.
L-arginine vs L-citrulline vs beetroot
L-citrulline is an amino acid the body converts into arginine, and it raises blood arginine more reliably than arginine itself because less is broken down on the way. Beetroot juice works by a different route: its nitrate is turned into nitric oxide. All three are sold for blood flow and exercise.
| Option | How it raises nitric oxide | Good to know |
|---|---|---|
| L-arginine | Direct building block | Much is broken down before reaching the blood |
| L-citrulline | Converted to arginine in the kidneys | Raised blood arginine more than arginine in a head-to-head study |
| Beetroot juice | Nitrate turned into nitric oxide | Mouthwash can blunt the effect; see our beetroot guide |
Read beetroot juice benefits and side effects for the nitrate evidence, and creatine if exercise performance is your goal: it has much stronger evidence than arginine.
Which foods are high in arginine?
The richest food sources of arginine are pumpkin seeds, peanuts and other nuts, followed by meat, poultry, fish, dairy, soya, lentils and chickpeas. Because arginine is part of protein, anyone eating enough protein from a mix of foods gets several grams a day without a supplement.
- Seeds and nuts: pumpkin seeds, peanuts, almonds and walnuts. See pumpkin seeds benefits.
- Animal protein: chicken, turkey, beef, pork, fish and dairy.
- Plant protein: soya, tofu, lentils, chickpeas and other beans.
If you are eating more protein for training, our muscle recovery guide covers timing and amounts.
L-arginine side effects and medicines
L-arginine can cause stomach pain, bloating, nausea and diarrhoea, especially at several grams a day. Because it can lower blood pressure, it may add to the effect of blood pressure medicines, nitrates and erection medicines such as sildenafil. It should not be taken after a heart attack.
- After a heart attack: in a US trial, people given L-arginine after a heart attack had more deaths than those on placebo. Don’t take it unless your cardiologist advises it.
- Nitrates for angina (GTN spray or tablets, isosorbide mononitrate): the NHS warns GTN with other medicines that lower blood pressure can make it drop too low. Speak to your GP or pharmacist first.
- Sildenafil, tadalafil and similar medicines: these also widen blood vessels, so check with your GP or pharmacist before combining them with arginine.
- Blood pressure medicines: arginine could lower your blood pressure further. Signs of low blood pressure include dizziness and fainting.
- Diabetes medicines: arginine can affect blood sugar, so ask your GP or diabetes team first.
- Cold sores: in lab studies the herpes virus uses arginine to multiply, so people who get frequent cold sores are often advised to be cautious. Human evidence is limited; see cold sores.
- Also check first if you have kidney or liver disease, low blood pressure, are due an operation, or are pregnant or breastfeeding. Not for children unless prescribed.
iIf you take any regular medicines, check with your GP or pharmacist before starting L-arginine.
Next step
Magnesium Glycinate Sleep Complex
Most people get enough arginine from protein foods. For everyday energy, Evopure’s Magnesium Glycinate Sleep Complex gives 290mg of magnesium (77% NRV) per 4.75g serving in a berry drink. Magnesium contributes to electrolyte balance, normal muscle function and a reduction of tiredness and fatigue.
Add Magnesium Glycinate Sleep Complex to bag
Subscribe and save 25% on your first order, then 20%. New to Evopure? Join our emails for 20% off a one-off first order. Free UK delivery over £45. If you take any regular medicines, check with your GP or pharmacist first. We don’t recommend our products during pregnancy or breastfeeding.
Subscribe £22.49One-off £29.99
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The FSA’s 10mg a day figure is precautionary advice rather than a legal limit, set while longer-term safety research continues. At Evopure we think it is a very cautious figure, and many adults use more. If you go above it, increase slowly, and check with your GP or pharmacist first if you take any medication.
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Sources 11
- Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. GOV.UK.
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2011). Scientific opinion on the substantiation of health claims related to L-arginine. EFSA Journal.
- NHS. Taking glyceryl trinitrate (GTN) with other medicines and Sildenafil (Viagra).
- NHS. High blood pressure.
- Dong JY et al (2011). Effect of oral L-arginine supplementation on blood pressure: a meta-analysis of randomized, double-blind, placebo-controlled trials. American Heart Journal.
- Rhim HC et al (2019). The potential role of arginine supplements on erectile dysfunction: a systemic review and meta-analysis. Journal of Sexual Medicine.
- Schulman SP et al (2006). L-arginine therapy in acute myocardial infarction: the VINTAGE MI randomized clinical trial. JAMA.
- Schwedhelm E et al (2008). Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine. British Journal of Clinical Pharmacology.
- King DE et al (2008). Variation in L-arginine intake follow demographics and lifestyle factors. Nutrition Research.
- Shao A, Hathcock JN (2008). Risk assessment for the amino acids taurine, L-glutamine and L-arginine. Regulatory Toxicology and Pharmacology. Authors from the Council for Responsible Nutrition, a US supplement industry body.
- FSA. Cannabidiol (CBD) guidance.
This guide is general information, not medical advice. Evopure doesn’t sell L-arginine.
