One possibility is medical marijuana, with sufficient precautions that it stays medical. I don't know exactly what level of precautions would be optimal, but you could do a lot better than we have now.
precautions
Always try to keep in mind that precautions are not free. Precautions stop a lot of people now from getting enough pain killing medication. I have experienced this myself, for 6 hellish weeks.
Over at Scott Adams' Blog you can find a very fine example of using the 'Rationality Engine' to solve the social problem of assisted dying.