Category: receptor_pharmacology
Explains the two most-reported melatonin phenomenology shifts: (a) more vivid, longer, more emotionally intense dreams the night-of, and (b) lingering grogginess on waking — both more pronounced at the high doses (3-10 mg) typical of US OTC products than at the physiologic-mimic dose (~0.3 mg) the pharmacology actually supports. Melatonin acts at MT1 and MT2, Gi/Gq-coupled GPCRs in the SCN (Brzezinski 1997 NEJM review); MT1 mediates the sleep-promoting effect, MT2 the phase-shift effect. Zhdanova 2001 showed that 0.3 mg produces plasma levels approximating physiologic nocturnal peak and is sufficient for sleep-onset assistance in older insomnia; 3-10 mg pushes plasma to supraphysiologic peaks that persist into morning, explaining the grogginess. Burgess 2010 mapped the phase-response curve at 0.5 vs 3.0 mg and showed comparable peak phase-shift magnitude — the higher dose is not more effective, just longer-lasting. The vivid-dream phenomenon is REM-rebound-like: melatonin appears to consolidate REM and increase REM density (proposed mechanism: MT2-mediated facilitation of REM sleep generators in the pons + suppression of early-night arousals → more REM total) — but the strong-dose effect is also explained by morning-rising plasma overlap with normal endogenous SCN melatonin rise. Auger 2015 AASM guideline supports low-dose, well-timed melatonin (1-3 mg, 30-60 min before desired sleep) and explicitly notes the dose-grogginess relationship; Costello 2014 found grogginess and headache as the most common AEs. Mitigation: lower dose (0.3-1 mg), take 30-60 min before lights-out, prefer immediate-release over sustained-release for the dream/grogginess profile.