L-Citrulline
L-citrulline is a non-essential amino acid and dietary supplement that raises plasma arginine and nitric-oxide availability more effectively than oral arginine itself. It is used for the training 'pump', modest blood-pressure and endurance effects, and as a mild erectile-function aid. Effects are real but small; it is a food-grade supplement, not a drug.
01 Overview
Orally, L-citrulline bypasses first-pass metabolism that limits arginine, is converted to arginine in the kidney and raises circulating arginine and nitric-oxide production more efficiently than arginine supplementation. Higher NO promotes vasodilation, which underlies its use for the muscle 'pump', small improvements in exercise tolerance, and mild erectile support.
Evidence is mixed and effect sizes are modest: a small controlled study found improvement in mild erectile dysfunction, and citrulline malate is popular pre-workout though the ergogenic data are inconsistent. It is well tolerated, with occasional mild GI upset, and is freely available as a supplement. It should be used cautiously alongside PDE5 inhibitors or antihypertensives given additive vasodilation.
02 Mechanism
Converted to L-arginine in the kidney, increasing nitric-oxide synthase substrate and NO-mediated vasodilation more effectively than oral arginine.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Erectile / vascular support | 1.5–3 g/day | Oral | L-citrulline dose used in the mild-ED study and for general vascular support. |
| Pre-workout (citrulline malate) | 6–8 g | Oral | Citrulline malate dose commonly used pre-training for the 'pump'. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Increased nitric oxide / 'pump'Raises plasma arginine and NO; increased muscle blood flow and perceived pump pre-workout. | modest | Observational | |
| Mild erectile-function improvementA small placebo-controlled study reported improvement in mild erectile dysfunction, weaker than PDE5 inhibitors. | small | Observational |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Mild gastrointestinal upsetOccasional bloating or stomach discomfort, especially at higher doses. | Mild | Uncommon | Anecdotal | |
| Additive hypotensionMay add to the blood-pressure-lowering effect of PDE5 inhibitors and antihypertensives. | Mild | Rare | Anecdotal |