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Adverse Effects of Methadone

From: Chapter 3: The Fundamentals of Methadone Maintenance Treatment, in Methadone Maintenance: A Counsellor's Guide to Treatment (© 2003).

In addition to its desirable effects (relieving opioid withdrawal and craving), methadone, like any other medication, may also cause a number of undesirable (adverse) effects. Some of these adverse effects (when they occur) tend to be persistent, while others tend to subside over time.

Given the length of time clients remain in MMT, concern about its adverse effects is fully justified.

The more common and more persistent adverse effects of methadone include the following:

  • sweating
  • constipation
  • changes in sexual desire and functioning
  • insomnia (U.S. Department of Health and Human Services, 1995).


Adverse effects of methadone that subside over time include the following:

  • reduced appetite; weight gain
  • nausea
  • drowsiness
  • tension, nervousness
  • headaches; body aches and pains (including "bone" aches)
  • chills (U.S. Department of Health and Human Services, 1995).


The adverse effects of other opioids are similar to those of methadone. When used at higher doses for severe pain or opioid dependence, therapeutic doses of opioids may also (initially) induce a sense of tranquillity and decreased apprehension.


Other adverse effects that have been associated with methadone include the following:

  • flushing, blushing
  • vomiting
  • dizziness, lightheadedness, unsteadiness, faintness
  • itching
  • constriction of airways
  • dry mouth
  • difficulty passing urine
  • reduced or absent menstrual cycle
  • dysphoria
  • palpitations (heart pounding)
  • swelling of feet and ankles
  • dental problems
  • muscle and joint pain
  • arms and legs feeling heavy
  • sleepiness
  • abdominal cramps.


Without minimizing the adverse effects of methadone, the following should be noted:

  • Not all clients will experience all adverse effects.
  • Many adverse effects are rare and will only be experienced by a few clients.
  • Different clients experience different adverse effects.
  • Most clients become tolerant to some adverse effects.
  • An adverse effect may be the consequence of too high a dose (intoxication) or too low a dose (withdrawal).
  • Adverse effects experienced with methadone may be more bothersome even if they are similar to or milder than adverse effects clients have experienced with other opioids.
  • Some adverse effects may not be disabling and may only be minimally bothersome.
  • Some adverse effects can be prevented or treated.
  • It is likely that factors other than the effects of methadone contribute to some of the adverse effects associated with methadone.