L-Citrulline
A nitric oxide precursor. More reliable at raising blood arginine than arginine itself.
L-citrulline is a non-essential amino acid the body converts into arginine, the direct precursor of nitric oxide, which relaxes blood vessels and improves blood flow to working muscle. Paradoxically, taking L-citrulline raises blood arginine levels more reliably than taking arginine itself, because a large share of oral arginine is broken down by the gut before it reaches circulation. Straight L-citrulline is the cleanest form for measuring dose; citrulline malate combines it with malic acid at either a 2:1 or 1:1 ratio, the 2:1 form being the one most sports research uses at a typical 6-8g pre-workout dose. Effects are on endurance and perceived effort rather than one-rep strength.
Reference values
Daily reference values from official nutrition authorities. These are population reference figures, not personal recommendations.
| RDA | Upper limit | Source |
|---|---|---|
| 6000 mg | No UL set | UK |
Forms and bioavailability
Not all forms are absorbed equally. The form on your supplement label affects how much your body can actually use.
| Form | Absorption | With food | Timing | Evidence |
|---|---|---|---|---|
| citrulline malate (1:1) | Typical | Either | Either | Likely |
| citrulline malate (2:1) | Typical | Either | Either | Strong |
| L-citrulline (free form) | Typical | Either | Either | Strong |
How it pairs with other supplements
Works well with
Distinct ergogenic mechanisms: citrulline (NO-mediated blood flow) + beta-alanine (carnosine buffering) cover both oxygen delivery and acid buffering.
Stack Almanac tracks which citrulline form you're taking and highlights the classic pairing with beta-alanine, since the two cover distinct sides of the pre-workout equation despite sharing a shelf.
Track your L-Citrulline in Stack Almanac
Last reviewed: 2026-07-22. Reference values are adult-general RDAs from UK. Individual needs may vary. This page is for informational purposes only and is not a substitute for professional medical advice.