Common (>10% users): Mild GI upset (nausea, indigestion) at higher doses (20 mg+) or on empty stomach. Mild headache — most often when choline cofactor is inadequate (same pattern as all racetams). Daytime sleepiness intermittently reported.

Less common (1-10%): Anxiety/nervousness (some users feel keyed-up rather than calmed — opposite of the typical anxiolytic report; suggests population variability in cholinergic response). Fatigue at very high doses. Mild irritability.

Rare-serious (<1% but worth knowing): None documented in the published literature. The Phase 2a trial at 240 mg/day for 6 weeks reported a placebo-comparable AE profile with no serious adverse events. Long-term safety data does not exist — no human use beyond the 6-week trial has been formally documented, so chronic-use safety is unknown.

Specific watch periods: First 1-2 doses for headache (resolve with adequate choline). First week for GI tolerance. No SJS/DRESS-type rash signals (this is not a typical concern for coluracetam).

Theoretical concerns: Sustained CHT1 up-regulation at the synaptic membrane is unstudied beyond 6 weeks. Whether continuous daily use causes adaptive down-regulation (coluracetam tachyphylaxis) or trafficking exhaustion is unknown. The PRN dosing pattern most users adopt likely circumvents this issue but it's not proven.