GABA

Gamma-aminobutyric acid is the brain's principal inhibitory neurotransmitter, and it is the target of benzodiazepines, alcohol, gabapentinoids and most sedative-hypnotics. That pharmacology creates an intuitive but misleading case for swallowing GABA itself. The blood-brain barrier expresses very limited transport for GABA, and the transporters that do exist largely move it out of the brain rather than in. Human studies measuring central penetration of oral GABA are sparse and unconvincing.

What the small trials do show is a change in EEG activity — increased alpha and decreased beta power — within thirty to sixty minutes of a 100 mg dose, alongside modest self-reported reductions in acute stress during arithmetic or public-speaking tasks. These are real signals, but they are more plausibly explained by GABA receptors on the enteric nervous system and vagal afferents than by direct cortical action. Fermented forms such as PharmaGABA, produced by Lactobacillus hilgardii, are the ones used in most of the published work.

For sleep, the evidence is thinner still: a handful of studies report shorter sleep latency at 300 mg taken an hour before bed, mostly in small Japanese and Korean cohorts with short follow-up. Compared with the trial base behind magnesium glycinate, L-theanine or CBT-I, GABA sits well down the list. It is inexpensive, well tolerated and unlikely to hurt you, which is a different claim from working.