I suggest Melatonin.
I wouldn't. I would suggest 25-50 mg of Diphenhydramine. You may not get as restful of a sleep as you may need, but you will knock straight out for 8 hours or so. That is just in the short term, if the insomnia condition is as bad as idioticidioms says, then I would suggest going to the doctor pronto to get something better.
I have issues with Melatonin and here is why (ready for another Chrono Eric chemistry sciency post?):
Yes, melatonin is the natural regulator hormone of sleep in the body. However, Melatonin is N-acetyl-5-methoxytryptamine. The N-acetyl group conveys a great degree of polarity to the molecule, and large polar molecules cannot cross the blood-brain barrier with ease unless they have a transport protein specifically for them or one that they can piggyback on. Additionally, 5-MeO tryptamines are notable serotonin agonists and psychedelic drugs. So notable, in fact, that the famous chemist Alexander Shulgin published a synthesis of Melatonin in his book TiHKAL and several people experimented with various doses in an attempt to obtain psychotropic effects, but to no avail. The subjects didn't even report sleepiness. This is especially interesting considering that 5-MeO tryptamine itself is a potent hallucinogenic drug. This strongly suggests that the Acetyl group conveys so much polarity that significant amounts of exogenous melatonin do not cross the blood brain barrier. The exception, of course, is if there is a receptor for melatonin specifically in the area of the pineal gland where it is naturally synthesized.
Nonetheless, melatonin does seem to induce sleep and promote REM dreaming. It also seems to have other benefits. However, the dosages for each individual seem to vary greatly. Taking anywhere from 3-10 mg of melatonin, I can safely say, does jack shit to me except possibly induce a placebo effect. I've found its sleep-inducing capabilities to be much worse than diphenhydramine, and after taking melatonin for a long term in an attempt to adjust my circadian rhythm - I saw no significant results at all. Other people have reported positive results with as little as 0.3 mg, with higher doses being completely ineffective. Furthermore, I would tend to wake up about 3-4 hours after falling asleep, with no desire to return to sleep at all. With diphenhydramine, I can sleep straight through the night without waking.
I think that the dosage problem with Melatonin is too much of a pain to jack with, especially with insomnia. If you are looking for an effective and short-term sleep aid, diphenhydramine beats out melatonin any day.
