dr. mccaul: with heroin, they become nauseous, they develop muscle aches, they get gooseflesh. they can't sleep. they have the "cold turkey" which you hear talked about and the "kicking the habit" actually comes from the fact that the muscle spasms, the legs will often have muscle spasms and muscle aches, and they literally are kicking in their sleep, and kicking through their unrest. narrator: to provide a smoother, less painful transition, many treatment programs use substitute drugs, such as methadone for heroin users. the dosage is slowly reduced, as the addict adjusts to a drug-free existence. to ask people to taper from their drug of choice or substance of choice isn't successful, because if they could do that, they certainly wouldn't need medical treatment. so what we ask them, is can we give you a substance similar or cross-tolerant, meaning that it works similarly in the brain as the substance of choice. dr. bigelow: the great advantages of drugs like methadone and lam are that they're orally effective, slow onset, long duration of action. so they prevent fluctuations