What’s the half-life of melatonin, anyway?
The half-life refers to the amount of time required for the concentration of a drug or supplement to be reduced by 50% in your blood.
The half-life of melatonin is about 35-60 minutes, depending on individual variability. This means that roughly ~45 minutes after ingestion, the concentration of melatonin in your blood will be reduced by 1/2. You’ll notice that melatonin has a relatively quick half-life (the pharmacologists will say that it has “rapid pharmacokinetics”).
Most doctors and scientists recommend taking melatonin at least 2 hours before bed (rather than right at bedtime). This is because melatonin release signals to your brain that nighttime is approaching and it’s time to wind down in preparation for sleep.
So if the half-life of melatonin is ~45 minutes, and we’re supposed to take melatonin 2 hours before bed, won’t most of the melatonin you just ingested be out of your system by the time you go to bed. Well, yes, that is technically true. But melatonin is a chronobiotic – it helps your body entrain itself to cues in your environment, especially light and temperature. Even if you take melatonin hours before bed, it will affect your sleep because melatonin supplementation causes a circadian phase advance.