[I am not a sleep specialist. Please consult with one before making any drastic changes or trying to treat anything serious.]

Van Geiklswijk et al describe supplemental melatonin as “a chronobiotic drug with hypnotic properties”. Using it as a pure hypnotic – a sleeping pill – is like using an AK-47 as a club to bash your enemies’ heads in. It might work, but you’re failing to appreciate the full power and subtlety available to you.

Melatonin is a neurohormone produced by the pineal gland. In a normal circadian cycle, it’s lowest (undetectable, less than 1 pg/ml of blood) around the time you wake up, and stays low throughout the day. Around fifteen hours after waking, your melatonin suddenly shoots up to 10 pg/ml – a process called “dim light melatonin onset”. For the next few hours, melatonin continues to increase, maybe as high as 60 or 70 pg/ml, making you sleepier and sleepier, and presumably at some point you go to bed. Melatonin peaks around 3 AM, then declines until it’s undetectably low again around early morning.

Is this what makes you sleepy? Yes and no. Sleepiness is a combination of the circadian cycle and the so-called “Process S”. This is an unnecessarily sinister-sounding name for the fact that the longer you’ve been awake, the sleepier you’ll be. It seems to be partly regulated by a molecule called adenosine. While you’re awake, the body produces adenosine, which makes you tired; as you sleep, the body clears adenosine away, making you feel well-rested again.

In healthy people these processes work together. Circadian rhythm tells you to feel sleepy at night and awake during the day. Process S tells you to feel awake when you’ve just risen from sleep (naturally the morning), and tired when you haven’t slept in a long time (naturally the night). Both processes agree that you should feel awake during the day and tired at night, so you do.

When these processes disagree for some reason – night shifts, jet lag, drugs, genetics, playing Civilization until 5 AM – the system fails. One process tells you to go to sleep, the other to wake up. You’re never quite awake enough to feel energized, or quite tired enough to get restful sleep. You find yourself lying in bed tossing and turning, or waking up while it’s still dark and not being able to get back to sleep.

Melatonin works on both systems. It has a weak “hypnotic” effect on Process S, making you immediately sleepier when you take it. It also has a stronger “chronobiotic” effect on the circadian rhythm, shifting what time of day your body considers sleep to be a good idea. Effective use of melatonin comes from understanding both these effects and using each where appropriate.