Long-term Effects of Methadone

Common side-effects from prescribed methadone can include:

• Constipation
• Excessive sweating
• Dry mouth
• Changes in sex drive
• Drowsiness
• Light-headedness
• Nausea and vomiting
• Weight gain

As with any opioid, methadone can cause respiratory depression and cardiac arrest. Because of the slow onset of action, the progression of respiratory depression in a person taking methadone is insidious, and can go unnoticed by the patient’s companions. An added risk factor is methadone’s long half-life of 24 hours or more. Serum methadone level will increase with each successive dose until it reaches steady state (this takes four to five half lives). During early induction, the new patient is at risk of overdose and death. Taken together, these factors make methadone a medication that has to be handled with respect, by clinicians who understand its properties and its dangers. Mixing opioids with other drugs also increases the risk of overdose. If you or someone you know uses opioids, it is a good idea to have a free naloxone kit. Naloxone is a medication that can temporarily reverse the effects of an opioid overdose and allow time for medical help to arrive.

If the methadone dose is too high, the following symptoms may be experienced. Call an ambulance straight away by calling 911 in Ontario if you or someone else has any of these symptoms:

• Depressed breathing, stupor or coma due to accumulation of the drug
• Severe constipation with obstruction of the bowel, or inability to pass urine
• Marked allergic reaction, with swelling of the face, lips, tongue and throat, wheezy breathing or tight chest
• Intense red rash with itching or hives
• Collapse

The dose of methadone should be reduced or treatment discontinued if the patient experiences moderate to severe side-effects as discussed above.  A patient may decide to wean off MMT if their use of illicit opioids has declined as reflected by negative or “clean” urine drug screens, and their socio-economic situation has improved. The best strategy to wean off MMT is to reduce the dose of methadone slowly by about 10% per week.  On the other hand, a patient has the option to switch to Suboxone® by a slow reduction in methadone while simultaneously increasing Suboxone® in a slow-step fashion over the span of about one week.

In the absence of pharmacological intervention, a person who has an opioid addicted  has roughly a 15% chance of succeeding in recovery. Many patients who discontinue methadone relapse within a year of stopping treatment.  Methadone causes physiological dependence and will result in physical and psychological withdrawal symptoms if discontinued abruptly.  The best strategy to wean off MMT is to reduce the dose of methadone slowly by about 10% per week.

Methadone withdrawal symptoms include:

Methadone withdrawal develops more slowly and is less intense than withdrawal from heroin. Withdrawal symptoms include: 

• Chills
• Fever
• Anxiety
• Muscle aches and pains
• Nausea
• Vomiting
• Sweating
• Rapid heartbeat
• Stomach cramps
• Irritability
• Paranoia
• Diarrhea
• Cravings
• Insomnia
• Hallucinations
• Depression