Melatonin dosage: why less works better
The most widely misunderstood aspect of melatonin pharmacology is the dose-response relationship: most research suggests that less is more, and that the doses sold in standard supplement products (5 mg, 10 mg) substantially exceed what the circadian system requires.
The 0.5 mg finding
Multiple clinical studies have found that doses around 0.5 mg produce circadian phase shifts comparable to much larger doses. A 1995 study by Lewy and colleagues demonstrated that 0.5 mg at the right time was as effective as 20 mg for shifting circadian timing, with the higher dose producing significantly more grogginess the following day. This is a ceiling effect: the melatonin receptor system becomes saturated at low concentrations, and more melatonin above that threshold mainly adds sedation.
Why standard products are so much higher
The 5 mg and 10 mg doses that dominate supplement shelves reflect market preferences (consumers equate higher doses with stronger effect) and the loose regulatory framework for supplements, which does not require efficacy evidence at the labeled dose. Melatonin is classified as a dietary supplement in the US rather than a drug, so the dose relationship does not need to be demonstrated before sale.
Morning grogginess and the half-life
The morning grogginess many people attribute to melatonin 'still being in the system' is almost always a dose effect rather than a clearance issue. With a 20-45 minute half-life, even a 10 mg dose drops below 1% of its starting amount within roughly 3-4 hours. By morning the pharmacology is essentially gone. The grogginess is more likely from oversedation than from residual blood levels.
Not medical advice
This content is for informational purposes only. It is not a substitute for advice from a qualified healthcare professional and should not be used to make medication, dosing, or health decisions.