I have done this myself three separate times because I am studying brain signalling during sleep. I can tell you from personal experience you will have a hard time sleeping the next two nights. You will also have a very unusual (being polite) sensation in your head. They call it a Melatonin Hangover. I can best say it is like a headache, but the pounding is focused deep in the brain on top of the brain stem. It takes at least the three following days to get rid of. Unless your doing scientific research I highly do not recommend it. I can say I can do 20 mg without any after effects. So if your gung-ho about trying something .. limit it to 20 mg if you really must.