You don't have to stop smoking at all! This is all part of my doctors plan for me BTW. You can keep smoking while getting onto subs. Just start at a really low dose of sub. Like a half a MG. The goal is to taper off fent completely Yes but you can completely counteract the sickness that the fent causes by smoking it. If that makes sense. Like Yes, if fent is in your system while you take subs it'll put you into precipitated withdrawal but all you have to do to get out of that withdrawal is smoke a few hits of fent and you're good to go. I was smoking like a half gram a day now I'm up to 12mg subs and about $5 worth of fent a day