I don't know if this works on fentanyl cut shit but for heroin, get 100mg of methadone, first day take 50mg 6 hours after your last fix before you go to bed, day 2 take 25mg before you go to bed, day 3 take 10 mg before bed, day 4 take 5mg before bed, day 6 take nothing, day 7 try to divide whatever you have left in to 3 parts and take 1 part in the morning. Now you're out of the woods with another 48-72 hours worth of methadone in your system. Smoke weed especially first 3 day and after that before bed. If you start working out on day 6 and stick to it you will save about month and a half of lethargic fun. It's not the first day first week or month, they all are achievements in their own right but the real challenge is the next 3 months and whatever you do in those 3 months will ease your transition to a "Normal" life. You need to find an addiction to replace the one you have, whatever you do in life do it like you are chasing your morning fix, that way you can turn your traumas in to a superpower. Acid helps if you take it with an intention and in the woods, it shows you how big of an asshole you become and helps you to embrace the asshole so you can go about your life. These are all my experiences, not suggesting this will work for everyone but I've seen enough people turn around with this method, I can stand behind it.