I have some history on methadone:

1) It used to be a brand name, Dolophine. And at one time when there were few opiates available, it was used for severe pain.
Like Cancer. At one time it was a legit pain management option.
It is not just for detoxing heroin addicts.

2) methadone is the generic name and is a useful alternative because it does not cause the euphoric highs that other opiates do (esp heroin), so it can be used to detox heroin without the "pleasure" which is the addictive part. It is very cheap and works for some PNers in very low doses.

I do think doctors are going to be resistant in giving a young person opiates.

That history of back pain you have, Sarah, and your lack of PN in the hands, bothers me. A nutritional cause would be affecting your hands too. I think getting another opinion in your case might be helpful. If your pain in your toes and legs is due to compressed nerves in the spine, a solution for that may present itself. But that would be your decision. Most PNers go thru many diagnostic opinions. Codeine is not a good drug for chronic pain...it has to be activated in the liver before becoming useful.
http://www.medscape.com/viewarticle/420696