The dose used should be the lowest amount that works, such as 1 mg or less. Some users find that a dose as little as 0.2 mg can induce sleep. It is ok to accasionally take a high dose such as 5 or 10 mg if needed. Melatonin is not toxic at high doses when used infrequently. Tiredness, low mood, or fatigue can develop when people use melatonin every night, especially in doses more than 2 or 3 mg.
Some people feel sleepy the next day with the wish to take naps.
We still don't know the long-term effects on the immune and hormonal systems of chronic melatonin use. I'm 42 years old and I'm currently using 0.5 mg of melatonin about once or twice a week. Not only does melatonin provide me with a deep sleep, but there seems to be a carry over effect into following nights. The effect of taking it one night seems to influence my sleep positively for another night or two. Discusses the controversy, safety issues, and effectiveness.