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 (5mg, 10mg) substantially exceed what the circadian system requires.
The 0.5mg finding
Multiple clinical studies have found that doses around 0.5mg produce circadian phase shifts comparable to much larger doses. A 1995 study by Lewy et al. demonstrated that 0.5mg at the right time was as effective as 20mg for shifting circadian timing — with the higher dose producing significantly more grogginess the following day. The Cochrane jet lag review reached a similar conclusion. 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 5mg and 10mg doses that dominate supplement shelves reflect market preferences (consumers equate higher doses with stronger effect) and the FDA's 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, meaning the dose relationship does not need to be demonstrated to the agency's satisfaction before sale.
Morning grogginess and the half-life
The morning grogginess that 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 10mg dose drops below 1% of its starting amount within 6 half-lives — roughly 3-4 hours. By morning, the pharmacology is essentially gone. The grogginess is more likely from oversedation (higher dose than the receptor system needs) or from the dose disrupting sleep architecture rather 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.