Comparison guide
L-tyrosine or N-acetyl-L-tyrosine?
N-acetyl-L-tyrosine is more soluble and marketed as the superior form, but in a human study much of it was excreted unchanged rather than converted to tyrosine. All the stress-and-cognition evidence comes from plain L-tyrosine, at doses far larger than most capsules contain.
The options, compared
| Option | Evidence | Best for | The honest note | |
|---|---|---|---|---|
| L-Tyrosine | Moderate evidence | Acute stress and sleep loss | Preserves working memory under cold, noise or sleep deprivation at 100–150 mg/kg (roughly 7–12 g) taken 30–60 minutes beforehand. It does nothing reliable for rested, unstressed people. | View |
| N-Acetyl-L-Tyrosine | Limited evidence | Not worth the premium | An infusion study found it was largely excreted unchanged, and no trial has tested it for focus, mood or stress. Typical 300–500 mg servings are a small fraction of the tyrosine doses that worked. | View |
Our verdict
Plain L-tyrosine is what the stress and sleep-deprivation studies used and is much cheaper; skip N-acetyl-L-tyrosine. Take tyrosine only ahead of a specific acute stressor, and avoid it with MAO inhibitors, with hyperthyroidism, or with melanoma unless a doctor agrees.