In an interesting study, a male patient who lacked melatonin was given melatonin supplements. The patient's pineal gland had been destroyed 5 years earlier in the course of treatment for a pineal tumor. The administration of melatonin 0.5 mg to 2 mg significantly improved his sleep and mood (Petterborg, 1991).
Every medicine has an ideal dosage. Too high doses of melatonin may make some people tired and depressed, especially those who are prone to depression. Leonard, from Vancouver, British Columbia, writes, "I've used melatonin and it worked quite well. I've had problems getting to sleep all my life. It usually takes me about 2 hours to fall asleep and the melatonin reduced that to around a half hour, a miracle for me. I used either 3 or 6 mg depending on what I felt I would need on a given night. I slept fine without the morning grogginess from other stuff I've used over the years. I stopped using it because I noticed that I was feeling a little depressed and I suspected the melatonin. I've suffered from serious depression when I was younger— suicide attempts, the whole deal. It went away about 10 years ago. When I stopped using melatonin I returned to my usual (somewhat sleep deprived but not depressed) self again. I think it's important to look into this possible effect of melatonin. I wonder if someone has to be predisposed to depression to be affected by melatonin like I was. This experience was enough for me to give up using melatonin without regrets despite how well it worked for my insomnia." It's possible that Leonard's melatonin dose was too high for him. Since he does not sleep well, he may benefit from some additional melatonin. Perhaps his ideal dose is 0.5 or 1 mg.
Low amounts of melatonin produced by our pineal gland lead to poor sleep, and consequently cause next-day tiredness and low mood. Too high doses may also have negative effects on mood.
Melatonin doses need also to be adapted to the seasons, to menstrual cycles, to the types of food we eat, to levels of exercise, and so on. A great many factors influence melatonin levels, sleepiness, and mood. You are the best person to figure out your ideal dose.
In addition to its effects on mood, melatonin can diminish anxiety and stress. It can influence the same brain receptors that benzodiazepines, such as Valium, use to provide relaxation (Pierrefiche, 1993). However, benzodiazepines interact negatively with brain receptors involved with memory. Melatonin does not interact with these receptors, and thus does not appear to interfere with memory and learning (Neville, 1986).
We've seen how changing the patterns of our sleep cycles through traveling and shift work can produce unpleasant consequences. Just how did these sleep cycles come about, anyway? Evolutionary secrets now revealed tell a fascinating story.