L-arginine

What it is

Arginine is a semi-essential amino acid found in meat, fish, dairy, nuts and seeds. Your body uses it to make proteins, creatine and nitric oxide.

It became popular as a nitric oxide booster for sports, circulation and sexual function. Most healthy people get enough from food.

Supplements are taken as free-form L-arginine, arginine HCl or arginine alpha-ketoglutarate (AAKG).

How it works

Enzymes convert arginine to nitric oxide, which relaxes blood vessels. The catch is that much oral arginine is broken down in the gut and liver before reaching the blood, so supplementing often does not raise nitric oxide as much as the theory suggests.

What the evidence says

• Moderate Blood pressure reduction
  Some meta-analyses show small reductions, though results vary and it is not a substitute for treatment.
• Limited Erectile function
  Small trials with high doses show mild effect in some men; evidence is not strong.
• Weak Exercise performance and pumps
  Most trials in healthy trained people show no meaningful benefit.
• Limited Recovery and wound healing in specific clinical settings
  Used in specialised nutrition products under clinical supervision; not a general supplement claim.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• Typical studied range: 3 to 6 g daily, divided into 2 or 3 doses.
• Doses above about 9 g in one go often cause gut upset.
• Take with food if you get stomach discomfort.
• Long-term upper limits are not firmly set; check current guidance.

Forms and what to look for

• L-arginine free form or HCl: the standard and most studied.
• AAKG: sold for sports, little evidence it is better.
• Arginine in combination with citrulline may raise arginine levels more than arginine alone.
• Check grams of actual arginine per serving.

What to expect, and when

• You are unlikely to notice anything in a single dose.
• Any blood pressure effect would take several weeks of daily use and should be monitored.

Side effects

• Nausea, bloating, diarrhoea and abdominal cramps at higher doses.
• Low blood pressure and light-headedness.
• Flushing or headache.
• May worsen cold sores in people prone to herpes outbreaks, a commonly reported link.

Interactions

• Blood pressure medicines, nitrates and sildenafil-type drugs: additive blood pressure lowering.
• Potassium-sparing diuretics and ACE inhibitors: arginine can raise potassium.
• Diabetes medicines: possible effect on blood sugar.
• Anticoagulants: speak to a pharmacist.

Who should avoid it

• People who have had a heart attack: a trial using arginine after heart attack was stopped over safety concerns, so avoid unless advised by a clinician.
• Anyone with low blood pressure, kidney disease or asthma.
• People prone to herpes outbreaks.
• Pregnant or breastfeeding people.

Risks and safety

• Interaction with heart and blood pressure drugs is the main concern.
• Not banned by WADA but multi-ingredient products can contain prohibited stimulants.
• Doses well above 10 g a day are not well studied.

Buying well: quality and testing

• Look for single-ingredient products with stated grams per serving.
• Informed Sport or NSF certification for athletes.
• Be wary of pre-workouts with undisclosed blends.
• Avoid claims about curing blood pressure or erectile problems.

Bottom line

Arginine is cheap and generally tolerated, but the evidence for sports and circulation is underwhelming. If you take heart or blood pressure medication, or have had a cardiac event, speak with a clinician first. Citrulline is often a better route to the same goal.