The text above is a follow-up to ... -----Question-----. after taking a 80mg dose of methodone how long does it take for the effects to reach there peak or there maximum effect. -----Answer-----. Dear Charles, It takes about 4 hours for methadone to reach its peak concentration following oral administration. Some relief of pain occurs after 30 to 60 minutes and the duration of action is initially 6 to 8 hours.