L-Arginine
Also known as Arginine, L-Arg
L-Arginine is a semi-essential amino acid and the primary substrate for nitric oxide (NO) synthesis. Nitric oxide dilates blood vessels, improving circulation and blood pressure. Its use in athletic performance has largely been superseded by citrulline, which raises arginine levels more efficiently, but arginine retains strong evidence for cardiovascular and erectile function.
Benefits
Raises nitric oxide and improves blood flow
ModerateAs the direct NO precursor, arginine supplementation increases nitric oxide, dilates blood vessels, and improves circulation.
Supports blood pressure
ModerateMeta-analyses show modest but consistent reductions in systolic and diastolic blood pressure with arginine supplementation.
Erectile function support
ModerateNitric oxide is the key signalling molecule behind penile erection; arginine at higher doses (3–6 g/day) has shown benefit in mild erectile dysfunction.
Pros & cons
Pros
- Direct nitric oxide precursor — clear mechanism
- Useful for cardiovascular and sexual health
- Widely available and inexpensive
Cons
- Citrulline raises blood arginine levels more effectively with fewer GI side effects
- High doses needed for performance benefits
- Not recommended after heart attack (one large trial showed harm)
Side effects
GI upset
Bloating, diarrhoea, and nausea are common at high doses.
May worsen herpes outbreaks
Arginine promotes herpes simplex virus replication; people prone to cold sores or genital herpes should be cautious.
Blood pressure drop
Can lower blood pressure significantly; caution with antihypertensives.
How to take it
Typical dose
3–6 g per day for cardiovascular/ED benefit; 6–10 g pre-workout for performance
Timing
30–60 minutes before exercise for performance; spread throughout the day for cardiovascular goals
Common forms
Tip: Consider L-Citrulline instead for workout pumps — it is better absorbed and raises arginine levels more effectively.
What the research says
Arginine and blood pressure
ModerateMeta-analysis of RCTs shows arginine supplementation significantly reduces systolic and diastolic blood pressure.
Arginine and erectile dysfunction
ModerateSupplemental arginine (3–6 g/day) improves erectile function scores in mild to moderate ED in multiple controlled trials.
How it connects
Relationships between L-Arginine and other supplements in the matrix.
L-Citrulline converts to arginine in the kidneys far more efficiently than oral arginine; the two share the same nitric oxide pathway.
Compare the pairingVitamin C protects nitric oxide from oxidative breakdown, extending the vasodilatory effect of arginine.
Compare the pairingMagnesium supports vascular smooth muscle relaxation alongside nitric oxide from arginine.
Compare the pairingZinc is a cofactor for nitric oxide synthase, the enzyme that converts arginine to NO.
Compare the pairingImportant cautions
- Do not use arginine after a heart attack — a large trial (VINTAGE MI) was stopped early due to increased mortality.
- Caution with low blood pressure, antihypertensive medications, and Viagra/PDE5 inhibitors.
- May promote herpes simplex flares; consider pairing with lysine if prone.
More Amino Acids
Creatine
The most-studied performance and cognition supplement.
Glycine
A calming amino acid for sleep, collagen, and metabolic health.
L-Citrulline
A superior nitric oxide booster that outperforms arginine for pumps and endurance.