Hi
Methadone does indeed have a very long half life--up to 72 hours. Withdrawal from methadone takes much longer than withdrawal from other opiate drugs for this reason, although this is also the reason why it works so well for addiction treatment and pain control.
Methadone works great for a lot of people, but not for everyone. If you are feeling the way you describe, and a dose adjustment has not corrected the problem, then you may need a different treatment for your pain.
The suggested method for withdrawal from methadone is to reduce the dose by 10% every 2-4 weeks. You always measure the 10% based on the dose you are on NOW, not your starting dose. For example, if you are on 50mg, your first drop would be 5mgs, and then your next drop would be 4.5mgs, the next drop 4mgs, etc. It is crucial to success that you go all the way down to 1mg before stepping off. Otherwise you risk serious withdrawals.
Methadone withdrawals, if going cold turkey, can last weeks or even months--and I speak of the acute phase where you have the severe opiate withdrawal symptoms. The majority of those who try this route end up relapsing or returning to methadone treatment.
If you are still in need of medication to treat your pain you could ask the doctor to simply switch you to a different pain med. If, however, your wish is to be opiate free, I would strongly suggest following the tapering protocol I mentioned which is supported by most experts in the field of methadone treatment--your chances of long term success are much higher. I know it may seem like a pain, and it is easy to get impatient, but it is truly the best way--and if done correctly, there is no need to experience any undue suffering or illness.
Wishing you the best,
Zenith
Certified Methadone Advocate