Opiates

No, opiates are not cholinergic antagonists. Opiates are a class of drugs that primarily act on the opioid receptors in the brain to produce pain relief and euphoria. Cholinergic antagonists, on the other hand, block the action of acetylcholine at cholinergic receptors, affecting processes like muscle contraction and neurotransmission. Therefore, opiates and cholinergic antagonists have different mechanisms of action and effects on the body.

I am on methadone and have been for years. I am also taking college courses, one being Psych Substance Abuse and Addiction. The answer is until the methadone is out of your system. It may take days, weeks, or months. For me, it would take months, but if you took methadone but you're not used to taking it, probably a few days or so. Methadone does block the effects of heroin, which is why a lot of people use the methadone maintenance treatment programs. If I were to try to use heroin tomorrow, it would just be a waste of time and money because I wouldn't even feel it, and I would hella pissed, which is the purpose of it blocking the heroin. The withdrawal from methadone can take weeks or months, and it's more intense than heroin.