Methadone is a controversial addiction treatment medication that’s often used in a technique called methadone maintenance. This form of medication-assisted treatment (MAT) is designed to replace the use of more dangerous illicit opioids like heroin. Methadone is taken for up to a year and, in some cases, indefinitely, which is what makes it controversial.

Coming off methadone can be extremely difficult, and some report more intense withdrawal symptoms than heroin and other opioids. Because of this, methadone is becoming less popular than other MAT opioids such as buprenorphine. On the other hand, MAT and methadone have been shown to help remove people from a lifestyle of active addiction. Still, like any medication, methadone comes with potential side effects and adverse reactions.

Which side effects should be expected and which ones are potentially dangerous? Learn more about potential methadone side effects and which ones you should avoid.

Common Methadone Side Effects

Methadone is an opioid that primarily works by binding to the mu opioid receptor (MOR) and activating it. This is similar to other opioids that are used as pain relievers. However, methadone is as potent as other opioids because it has a lower affinity, which means it doesn’t bind as readily as other opioids.

This means that regular use as a MAT medication shouldn’t cause significant intoxication like a more potent opioid might. However, this psychoactive drug does have some significant effects on the brain and body that you may notice. It’s important to keep track of your symptoms and keep your doctor and medical team informed as to the effects of the medications you take. Some of the common effects you may encounter while using methadone include:

Mild Opioid Effects

Opioids bind to receptors all over the body so that they may cause effects throughout the body including in the brain, muscles, joints, and digestive system. As a psychoactive drug, it can also cause some common cognitive and psychological side effects including:

  • Sedation
  • Mood swings
  • Drowsiness
  • Insomnia
  • Memory issues
  • Anxiety
  • Nervousness
  • Depression

Methadone can also cause common physical side effects. Mild symptoms are normal but persistent or severe symptoms should be addressed immediately by speaking to your doctor. Common adverse effects include:

  • Headaches
  • Constipation
  • Flushing
  • Sweating
  • Weakness
  • Dry mouth
  • Itching

When your doctor first prescribes methadone, you should ask him about the symptoms you should realistically expect. If any symptom becomes too severe, you should let your doctor know as soon as possible.

Chemical Dependence

One of methadone’s major drawbacks is that using it to replace a more harmful drug means you will still be dependent on an opioid. Chemical dependency means your brain has adapted to a foreign psychoactive drug and integrated it into your normal brain chemistry. Using methadone will satisfy your brain’s need for that opioid to maintain balanced brain chemistry.

However, if you miss a dose or stop taking the drug altogether, that chemistry will become unbalanced, and you’ll start to experience unpleasant effects of withdrawal. To stop using methadone, you will have to go through a detox period where you are weaned off the drug. The safest way to do this is in a medical detox setting, but your doctors and clinicians will determine the best level of care when it’s time for you to stop using methadone.


Withdrawal is a consequence of chemical dependence, and it is a common side effect of methadone use. You may start to experience withdrawal symptoms when you miss a dose, take a smaller dose, or when you stop completely. Methadone withdrawal, as with other opioids, is often described as causing flu-like symptoms. People report that opioid-withdrawal causes some of the same symptoms as the flu but it’s generally worse than a typical case of the flu. Plus, methadone withdrawal is said to be particularly intense and may be difficult to get through.

Withdrawal Can Cause:

  • Lightheadedness
  • Increased tearing
  • Sensitivity to light
  • Runny nose
  • yawning
  • Sneezing
  • Nausea
  • Vomiting
  • Diarrhea
  • Fever
  • Sweating
  • Chills
  • Tremors
  • Tachycardia
  • High blood pressure

Opioid withdrawal symptoms aren’t known to be life-threatening, but they can be potentially dangerous if you go through it on your own. Symptoms like diarrhea, vomiting, and sweating can cause you to lose water quickly, leading to potentially dangerous dehydration.

If you are going through detox on your own, not paying attention to your hydration could lead to serious consequences. Withdrawal can also cause hypertension and tachycardia, which isn’t necessarily deadly to otherwise healthy users, but older people or people with cardiovascular problems could experience a heart attack or stroke if these symptoms aren’t addressed by a medical professional.

Side Effects That Should Be Avoided

Though there are a few symptoms of methadone use that you might be able to expect without causing any significant consequences, there are others that can be dangerous. If you experience severe or life-threatening symptoms, it’s important to seek medical help immediately. Common symptoms of methadone use that might require immediate medical or clinical attention include:

Abuse and Addiction

Though normal prescribed use of methadone doesn’t usually cause intoxicating effects, it can potentially be abused to achieve a euphoric high. During methadone maintenance, you will be given an appropriate dose each day, but if you obtain more illegally, you may start to abuse the drug. Abuse can lead to euphoria, heavy sedation, confusion, and drowsiness. Abuse can also lead to a severe substance use disorder that’s characterized by compulsive use despite the consequences.

Methadone addiction can be as potentially dangerous as an addiction to any other opioid. Prolonged use could lead to the use of illicit drugs like heroin when methadone becomes too difficult or expensive to obtain. Illicit opioid use increases your risk of experiencing serious consequences like an overdose.


High doses of methadone can lead to a potentially fatal overdose. A methadone overdose can suppress your central nervous system to a dangerous degree. The most common, life-threatening overdose symptom is respiratory depression, which is when your breathing slows or stops, leading to oxygen deprivation, coma, or death. Methadone overdose can be reversed with medical attention or with the opioid antagonist Narcan (naloxone).

Arrhythmias or Abnormal Heart RhythmsMethadone can sometimes cause abnormal heart rhythms or arrhythmias that can lead to serious medical complications. The drug can cause prolonged QT intervals, which is a measurement used in an electrocardiogram that measures the electrical pulse of a heartbeat. A longer pulse can lead to an arrhythmia that could lead to heart-related complications.

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