L-tryptophan, a protein building block from everyday foods sold as an oral supplement mainly for sleep and mood, shows modest, inconsistent benefits. The most consistent is fewer, shorter night-time awakenings; benefits for long life are unproven. The main safety concerns are a rare, sometimes fatal muscle and blood disorder linked to a contaminated batch, with lingering uncertainty about tryptophan's own part, and dangerous overstimulation with certain antidepressants. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Eosinophil count (CBC) | 0.0–0.5 × 10⁹/L | Safety check: rising eosinophils can signal EMS |
| ALT and AST | ALT about 7–55 U/L; AST about 8–48 U/L | Safety check: a rise prompts stopping |
| Plasma tryptophan | About 21–108 µmol/L; rise from own baseline tracked | Confirms intake and absorption |
| Kynurenine-to-tryptophan ratio | No established target; track change from own baseline | Kynurenine output rises with dose |
| C-reactive protein | Not specified in the ER | Inflammation context for the kynurenine-to-tryptophan ratio |
Cadence: Baseline before starting; blood count at 4 weeks, then every 3–6 months, and immediately if muscle pain, rash, swelling or breathlessness appears; liver enzymes at 3 months, then every 6–12 months; diary at 2 and 4 weeks, with use usually stopped if no benefit appears by 4 weeks