How do you fall asleep without using/relying on (legal) drugs?
Insomnia affects a lot of people. Here are steps to take in your everyday life to avert it.
1) Exercise regularly. If you live a relatively sedantary life, your body won't use much energy and, once bedtime comes, may not internally see a need to rest, contributing to insomnia.
However, by exercising for half an hour a day, whether with weights, cardio, playing sports, an aerobic routine, etc., you use energy and get your body's motor running. This will not only give you more energy during the day, but will sufficiently wear your body to where, once bedtime comes, it will want to rest.
Make sure, however, that you exercise in the morning or early afternoon, as you want to give your heart and body time to take advantage of the increased activity. If you exercise before bed, your circulation may still be moving at a higher rate at bedtime, and create the counterproductive problem of excaberating your insomnia.
2) Cut off sugar and caffeine in the afternoon and evening. In the case of coffee and tea, the idea is obvious, but even sugary products can have a similar effect to caffeine and keep you too wired to sleep. After dinner, forego dessert if you need to sleep that night. This also includes any alcohol, as most alcoholic drinks have some sugars in them, and alcohol itself can disrupt sleep patterns.
3) Relax and shut off the computer and TV before bed. Some people can fall asleep with the TV on, but usually the light source and noise can keep your mind moving at a time when it needs to start slowing down. Also, watching the news and seeing a bad story can create additional anxiety.
Being on the computer does even more to keep your mind moving, as the internet and other applications are more interactive. Get your business done about an hour before bed, and sit down with a book or another quiet hobby.
4) Again... relax. Most insomnia is generated from worries about life and personal problems. Most problems can't be solved late at night, so if anything's really bothering you, forget about it for the night and get some sleep. Worrying about it sure isn't going to fix the problem or help you get to sleep. You can deal with it in the morning if possible. If you can, try to do everything you can to take care of as many problems as you can during the day. If you're in an unavoidable situation, if you don't want to go to work or school in the morning, if you don't like your living situation... these are bigger problems that probably need to be addressed, whether or not you address your insomnia. Address these dilemmas and I'm guessing your insomnia may disappear.
These are starting points for dealing with insomnia. If problems or diet are keeping you awake, drugs certainly aren't going to help the bigger picture. Address any problems that are giving you anxiety in general, as they may be fueling your insomnia, and make changes to your lifestyle and diet that will help you get to sleep at night.