I agree methadone and buprenorphine are especially very difficult withdrawals to endure because of their super long half-lifes. It may not be as harsh and intense as a short-acting opiate will give, but they are very long and drawn out. Symptoms just lingering and lingering and lingering..... my last WD from one of those was from buprenorphine. I had been using it mostly via IV route for several months. My average dose per day was 6mg, but some days i may have only done 2mg cuz of supply shortages.
I wound up getting arrested for some trouble I got in about 5 or 6 hours after my last 2mg IV dose. I was taken to jail, and was OK for a couple days cuz of the long half-life buprenorphine has. Around the 2nd day or so, I could feel the bupe leaving my system little by little, and with each little bit leaving, I could feel withdrawal symptoms manifest themselves little by little. After the 4th day, you are in full-blown withdrawal. The RLS was so terrible I was beating on myself. My cell-mate thought I was crazy.
After enduring slow and agonizing pain for about 12 days, I finally had gotten the medical staff there to put my GABAPENTIN 800z on the med cart. They helped IMMENSELY. I finally got some sleep that night after going 12 days without a wink. My eyes felt like they were going to pop out of my skull from all the pressure of them not being able to get rested. Over about 3 weeks to 30 days most of the WD symptoms resolved themselves. Besides the flashes of profuse sweating and having to shit all the time , the symptom that annoyed me most and stuck around the longest was the EXCESS MOUTH SALIVATION. It just would not stop! The other symptom that got me pissed off the most and is potentially dangerous is the CONSTANT URGE TO URINATE. It was tough to deal with cuz I wad on a top bunk and kept having to hop down to go. But this is the bad thing, it kept me from wanting to hydrate myself, cuz it seemed every sip of water I'd take, within minutes it wanted to come out!
So that was a tough one. Not exactly the most intense but long and drawn out. Thank God I managed to get my GABA, cuz who knows how long it would have been before i got any sleep if i didnt. That makes you want to kill yourself cuz lack of sleep us very bad for mental health.
I have been thru oxycontin, hydrocodone, codeine, darvocet, etc .. and most of the other weak-moderate fast-acting withdrawals as well. They can be pretty intense at their peak, but the worst is over with in 3-5 days. Usually after 6 I start getting sleep back again.
My absolute harshest withdrawal was from when one of my dealers had been selling black tar heroin, and I was using it via IV for about 3 months straight. About .25g/day average. It had ridiculously long "legs". It took forever for WD to hit. Well into the next day after your last dose. I think like mentioned before about poppies and opium, this dope had many other alkaloids in it whiched caused the duration of it to last longer. It was SEVERE heroin withdrawal symptoms for about 13 days until they began subsiding. Man that one was bad.