15 mg melatonin: It's too high of a dose
15 mg of melatonin is unlikely to harm you, but it's too high of a dose. One thing that it's important to understand about melatonin is that doses above 0.5 mg aren't more effective. Melatonin's not like other drugs where taking more results in a more pronounced effect.
There's a "ceiling effect" at play, where 15 mg is just effective as 0.5 mg when it comes to regulating your circadian rhythm.
Effects from 15 mg Melatonin
You might experience the following side effects from taking too high a dose of melatonin:
- disrupted sleep
- mild sedation
Technically, 15 mg constitutes a melatonin overdose, but it's highly unlikely you will be harmed by ingesting 15 mg melatonin.
Effective melatonin dosage
Actually, 0.5mg is likely to be more effective than 15mg, because a 15mg dose will result in persistently elevated melatonin levels for the next 24hours. Check out the figure below. A 10mg dose of melatonin results in plasma melatonin levels that spike to 21,000 ug/mL. But even 12 hours, plasma melatonin levels are persistently elevated (1000 ug/mL) far above endogenous, normal levels.