Comparison
L-Theanine vs Glycine
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.
Glycine
Smallest amino acid, inhibitory neurotransmitter and sleep enhancer. NMDA co-agonist.
| Field | L-Theanine | Glycine |
|---|---|---|
| Category | amino-acid | amino-acid |
| Dose range | 100–400mg | 3000–5000mg |
| Half-life | 1h | 1h |
| Onset | 30min | — |
| Evidence | EVIDENCEA | EVIDENCEB |
| Safety | ●●●●● | ●●●●● |
| Legal (US) | USOTC | USOTC |
| PubMed refs | 720 | 980 |
The comparison in plain English
Auto-generated from dataL-Theanine and Glycine are both in the amino-acid category respectively. L-Theanine An amino acid found almost exclusively in tea leaves. Glycine Smallest amino acid, inhibitory neurotransmitter and sleep enhancer.
Bottom line
L-Theanine (evidence A, safety 5/5) has a weaker evidence base than Glycine (evidence B, 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 Glycine if
Glycine is the better fit when your goal aligns with its mechanism (The simplest amino acid and a direct inhibitory neurotransmitter at glycine receptors concentrated in the brainstem and spinal cord) and the dose range (3000–5000mg) suits your protocol. Half-life is 1h.