When methadone is taken under medical supervision, long-term maintenance causes no adverse effects to the heart, lungs, liver, kidneys, bones, blood, brain, or other vital body organs. Methadone
produces no serious side effects
, although some patients experience minor symptoms such as constipation, water retention, drowsiness, skin rash, excessive sweating, and changes in libido. Once methadone dosage is adjusted and stabilized or tolerance increases, these symptoms usually subside.