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Methadone side effects

Methadone oral tablet can cause extreme drowsiness and slowed breathing. This is more likely to occur during the first few hours after you take it and when your doctor increases your dosage.

Methadone can also cause other side effects.

More common side effects

The more common side effects of methadone can include:

  • constipation
  • nausea
  • sleepiness
  • vomiting
  • tiredness
  • headache
  • dizziness
  • stomach pain

If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.

Serious side effects

Call your doctor right away if you have serious side effects. Call 911 if your symptoms feel life-threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following:

  • Respiratory failure (not being able to breathe). Symptoms can include:
    • shortness of breath
    • chest pain
    • lightheadedness
    • feeling faint
    • slowed breathing
    • very shallow breathing (little chest movement with breathing)
    • dizziness
    • confusion
  • Orthostatic hypotension (low blood pressure when getting up after sitting or lying down). Symptoms can include:
    • low blood pressure
    • dizziness or lightheadedness
    • fainting
  • Physical dependence and withdrawal when stopping the drug. Symptoms can include:
    • restlessness
    • irritability or anxiousness
    • trouble sleeping
    • increased blood pressure
    • fast breathing rate
    • fast heart rate
    • dilated pupils (enlargement of the dark center of the eyes)
    • teary eyes
    • runny nose
    • yawning
    • nausea, vomiting, and a loss of appetite
    • diarrhea and stomach cramps
    • sweating
    • chills
    • muscle aches and backache
  • Misuse or addiction. Symptoms can include:
    • taking more of the drug than prescribed
    • taking the drug regularly even if you don’t need it
    • continuing to use the drug despite negative outcomes with friends, family, your job, or the law
    • ignoring regular duties
    • taking the drug secretly or lying about how much you’re taking
  • Seizures

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.

Methadone may interact with other medications

Methadone oral tablet can interact with other medications, vitamins, or herbs you may be taking. An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well.

To help avoid interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbs you’re taking. To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Examples of drugs that can cause interactions with methadone are listed below.

Drugs that you should not use with methadone

Do not take these drugs with methadone. Doing so can cause dangerous effects in your body. Examples of these drugs include:

  • Pentazocine, nalbuphine, butorphanol, and buprenorphine. These drugs may reduce methadone’s pain-relieving effects. This can cause withdrawal symptoms.

Interactions that increase your risk of side effects

  • Increased side effects from other drugs: Taking methadone with certain medications raises your risk of side effects from those drugs. Examples of these drugs include:
    • Benzodiazepines such as diazepam, lorazepam, clonazepam, temazepam, and alprazolam. Increased side effects can include severe drowsiness, slowed or stopped breathing, coma, or death. If you need to take one of these drugs with oxycodone, your doctor will monitor you closely for side effects.
    • Zidovudine. Side effects can include headache, tiredness, loss of appetite, nausea, and vomiting.
  • Side effects from methadone: Taking methadone with certain medications raises your risk of side effects from methadone. This is because the amount of methadone in your body is increased. Examples of these drugs include:
    • Cimetidine. Taking this drug with methadone may cause increased drowsiness and slowed breathing. Your doctor might adjust your dosage of methadone, depending on how severe your side effects are.
    • Antibiotics, such as clarithromycin and erythromycin. Taking these drugs with methadone may cause increased drowsiness and slowed breathing. Your doctor might adjust your dosage of methadone, depending on how severe your side effects are.
    • Antifungal drugs, such as ketoconazole, posaconazole, and voriconazole. Taking these drugs with methadone may cause increased drowsiness and slowed breathing. Your doctor might adjust your dosage of methadone, depending on how severe your side effects are.
    • HIV drugs, such as ritonavir or indinavir. Taking these drugs with methadone may cause increased drowsiness and slowed breathing. Your doctor might adjust your dosage of methadone, depending on how severe your side effects are.
  • Increased side effects from both drugs: Taking methadone with certain medications raises your risk of side effects. This is because methadone and these other medications can cause the same side effects. As a result, these side effects can be increased. Examples of these drugs include:
    • Allergy drugs, such as diphenhydramine and hydroxyzine. Taking these drugs with methadone may cause urinary retention (not being able to fully empty your bladder), constipation, and slowed movement in your stomach and bowels. This can lead to a severe bowel obstruction.
    • Urinary incontinence drugs, such as tolterodine and oxybutynin. Taking these drugs with methadone may cause urinary retention (not being able to fully empty your bladder), constipation, and slowed movement in your stomach and bowels. This can lead to a severe bowel obstruction.
    • Benztropine and amitriptyline. Taking these drugs with methadone may cause urinary retention (not being able to fully empty your bladder), constipation, and slowed movement in your stomach and bowels. This can lead to a severe bowel obstruction.
    • Antipsychotics, such as clozapine and olanzapine. Taking these drugs with methadone may cause urinary retention (not being able to fully empty your bladder), constipation, and slowed movement in your stomach and bowels. This can lead to a severe bowel obstruction.
    • Heart rhythm drugs, such as, quinidine, amiodarone, and dofetilide. Taking these drugs with methadone may cause heart rhythm problems.
    • Amitriptyline. Taking this drug with methadone may cause heart rhythm problems.
    • Diuretics, such as furosemide and hydrochlorothiazide. Taking these drugs together can change your electrolyte levels. This can cause heart rhythm problems.
    • Laxatives. Taking these drugs together can change your electrolyte levels. This can cause heart rhythm problems.

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