Hi. My Husband Has A Lot Of Trouble Sleeping. He'll

Hi. My husband has a lot of trouble sleeping. He'll sleep for a short period and then is wide awake. I was reading about melatonin and was wondering if this might possibly help him get a good night's sleep. If you feel this would be worthwhile trying, what amount should be taken, when, and for how long. Also, is it available over the counter? I realize that some people have side effects. Thank you.