TPH2
TPH2 tryptophan hydroxylase — the molecular target that 1 compounds in the wiki act on.
In one line: The factory enzyme that builds serotonin, your calm-and-contentment chemical.
TPH2 is the rate-limiting (slowest, controlling) enzyme that manufactures serotonin in the brain — the chemical behind calm, contentment, and healthy sleep. Supplements like 5-HTP skip past this bottleneck by supplying serotonin's near-finished ingredient directly.
Because they raise serotonin, they should never be combined with antidepressants — too much serotonin at once is dangerous.