Comparison
L-Theanine vs L-Citrulline
L-Theanine
An amino acid found almost exclusively in tea leaves. Promotes relaxed alertness via alpha-wave promotion and GABA/serotonin/dopamine modulation. Pairs with caffeine in a 1:2 ratio to produce the most-validated focus synergy in the nootropic literature. Essentially no side-effect or interaction profile at typical doses.
L-Citrulline
Amino acid converted to L-arginine, raising nitric oxide. Used for vasodilation, athletic performance, and ED.
| Field | L-Theanine | L-Citrulline |
|---|---|---|
| Category | amino-acid | amino-acid |
| Dose range | 100–400mg | 3000–8000mg |
| Half-life | 1h | — |
| Onset | 30min | — |
| Evidence | EVIDENCEA | EVIDENCEA |
| Safety | ●●●●● | ●●●●● |
| Legal (US) | USOTC | USOTC |
| PubMed refs | 720 | 1100 |
The comparison in plain English
Auto-generated from dataL-Theanine and L-Citrulline are both in the amino-acid category respectively. L-Theanine An amino acid found almost exclusively in tea leaves. L-Citrulline Amino acid converted to L-arginine, raising nitric oxide.
Bottom line
L-Theanine (evidence A, safety 5/5) matches the evidence base of L-Citrulline (evidence A, safety 5/5). L-Theanine has the slightly cleaner safety profile. For users new to either, the higher-evidence option is the safer first try.
Choose L-Theanine if
L-Theanine is the better fit when your goal aligns with its mechanism (Crosses the blood-brain barrier within ~30 minutes of oral dosing) and the dose range (100–400mg) suits your protocol. Half-life is 1h.
Choose L-Citrulline if
L-Citrulline is the better fit when your goal aligns with its mechanism (Citrulline bypasses arginine's poor oral bioavailability — it is absorbed efficiently from the gut, then converted to arginine in the kidneys, raising plasma arginine and nitric oxide more reliably than oral arginine itself) and the dose range (3000–8000mg) suits your protocol. Half-life is —h.