2/? The four questions you originally came up withwere good, even if you could only answer 3:
1. Do you want to do it?
2. Can you actually get it?
3. Can you afford it?
4. Can you handle the side-effects?
1 is important - it's not up to anyone else. 2 is just medical criteria. 3 is troubling but OK if it works. 4 is an unfair fucker of a question you'll have no idea how to answer until after you've tried, but so far so good!