Is melatonin any use for insomnia?

We asked Professor Russell Foster: Melatonin is a hormone produce in the pineal gland. It's highly regulated by light. It's produced at night. There's two bits of evidence to suggest it might be useful. 1, if you take melatonin about 70% of people will fall asleep; 2, it may help you shift your body clock. The evidence emerging is that yes, it may help you sleep. Chris - Is it harmful?

Russell - We don't have any evidence that it's harmful. I certainly wouldn't recommend using it without discussing with your GP first.