Hi,
Methadone's usefulness in treatment of opioid dependence is the result of several factors. It has cross-tolerance with other opioid including heroin and morphine and a long duration of effect, with the result that oral dosing with methadone will stabilize the patient by stopping the opioid withdrawal syndrome. Secondly, it's also possible to block the euphoric effects of heroin, morphine, and similar drugs but only in higher doses (60-80 mg+). As a result, properly dosed methadone patients can reduce or stop altogether their use of these substances.
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Rider21
Drug Treatment