Methadone Side Effects: A Comprehensive Guide

Methadone is a medically accepted drug but is often illicitly prescribed and used by people for chronic and severe pain. While it boasts of several medical uses, Methadone side effects may be dangerous and life-threatening.

It poses risks of addiction even when used rightly, leading to potential drug misuse. Methadone finds utility in the treatment of addiction to heroin and other opioids.

However, while healthcare professionals consider it a safer alternative to most narcotics, the drug poses a high risk of abuse and dangerous effects on the user. So, provides a comprehensive guide to methadone use and potential side effects.

Methadone Side Effects

What Is Methadone?

In case you’re wondering: what is methadone? It is a prescription drug used as an opioid to manage moderate to severe ongoing pain. According to the Substance Abuse and Mental Health Services Administration (SAMHSA), methadone is among the drugs listed as Medications for Opioid Use Disorder (MOUD). But its use as an opioid exposes people to drug misuse and dependence.

It comes in various forms: powder, tablet, and liquid. Methadone also has an intravenous (IV) form, which only a healthcare provider should administer.

Methadone also comes as Methadose, a brand name for an oral soluble tablet. Oral methadone tablets relieve patients from severe pain and are only necessary when other short-term, non-opioid medication fails.

How Does Methadone Work?

Methadone works as a long-acting opioid agonist. It acts on opioid receptors in the brain, blocking off their effects to reduce craving and withdrawal symptoms. It works on the brain to alter how the body responds to pain.

Although methadone activates the opioid receptors, it does so more slowly than other opioids. Also, in an opioid-dependent person, methadone administration does not produce euphoria, making it a preferable alternative in an opioid treatment program (OTP).

What Are the Side Effects of Methadone?

Despite having beneficial effects on opioid withdrawal, methadone is still an opioid and may pose several dangerous side effects. That said, what are the side effects of methadone?

Methadone can cause mild to severe side effects. The following list highlights the mild ones that may occur briefly while taking methadone.

Common Methadone Side Effects

  • Nausea
  • Constipation
  • Tiredness
  • Stomach pain
  • Headache
  • Vomiting
  • Dizziness
  • Sleepiness

While these side effects may be mild, they may also become severe. In that case, you should discontinue usage and visit your doctor.

Severe Side Effects

Some severe side effects of methadone include the following.

  • Respiratory failure: This condition makes breathing on your own difficult. The symptoms include shortness of breath, lightheadedness, slowed breathing, shallow breathing, chest pain, dizziness, and confusion.
  • Orthostatic hypotension: This form of low blood pressure occurs when the methadone user stands after sitting or lying down. The symptoms include dizziness or lightheadedness and fainting.
  • Physical dependence and withdrawal: This is also called substance use disorder, a condition where a person finds it hard to live normally without drug intake. Symptoms include restlessness, irritability, increased blood pressure, loss of appetite, dilated pupils, chills, sweating, diarrhea, vomiting, and fast heart rate.

    Short-Term Side Effects of Methadone

    While methadone is a milder opioid, it’s still a narcotic with a high probability of causing dangerous side effects. In the short-term, controlled methadone doses helps reduce pains, heroin withdrawal symptoms, and cravings. However, high doses and misuse can cause unpleasant side effects, euphoria, and addiction.

    Some people may notice unpleasant side effects on brief methadone usage, exposing them to physical or psychological harm.

    Mild Methadone Side Effects

    These include drowsiness, lightheadedness, urinary retention, gastrointestinal distress, sexual impotence, and dry mouth.

    • Sexual Impotence: A study published in the National Centre for Biotechnology Information found that methadone therapy can cause sexual impotence and decreased libido. It does so by blocking the synthesis of releasing gonadotropin and testosterone hormones.
    • Urinary retention: Urinary retention is among the many adverse effects of opioid abuse or opioid therapy. Methadone and other opioids induce urinary retention by binding to mu (µ) and delta receptors responsible for inhibiting parasympathetic nerves that innervate the bladder.

    If you notice these symptoms, discontinue usage and consult your doctor. But less serious methadone side effects may not require medical attention.

    More Severe Short-Term Side Effects

    • Irregular heartbeat: Methadone may interfere with electrical signals sent from the brain to the heart, leading to irregular heart rhythm (atrial fibrillation).
    • Fainting: Methadone can produce bradycardia and vasodilation effects, causing a drop in blood pressure when the person using it stands up quickly. In people with underlying heart problems, this could cause cardiomyopathy, leading to fainting.
    • Tremors: Methadone usage may cause involuntary shaking due to a sudden adrenaline surge that triggers increased nervous and muscle response.
    • Respiratory depression: Respiratory depression occurs primarily with methadone hydrochloride tablets and may be life-threatening.
    • Unstable gait: This makes someone to walk in an abnormal, unsteady, or uncoordinated pattern. Opioid usage may impair your balance, increasing the risk of falls and injury.
    • Death from overdose: People may die if the impact of methadone on the heart and respiratory system exceeds their tolerance range. Some overdose deaths from methadone often result from self-administration.
    • Anaphylactic (allergic) reactions: Cases of opioid-induced anaphylaxis are rare but possible. Anaphylaxis is a severe, sometimes life-threatening, immune reaction. Its symptoms may include fainting, collapse of blood vessels, edema, itchy skin, rashes and swelling, difficulty breathing, and death.
    • Seizures: Opioids, including methadone, due to their interaction with the nervous system, can cause convulsions and seizures. However, seizures are rarely present in opioid withdrawal. It mostly happens in complicated cases.

    Medical providers often start with the lowest possible dose to manage withdrawal symptoms and avoid other side effects. It may take time and effort to adjust and reach the ideal methadone dose for people undergoing addiction treatment programs.

    Long-Term Side Effects of Methadone

    Physicians prescribe methadone for pain as an alternative to stronger opioids. However, the relief it provides the patient may cause drug dependence in someone enduring chronic pain.

    That is why most caregivers hesitate to prescribe methadone to their patients. Those who do are often extra careful in monitoring the patient’s prescription for signs of misuse or dependence.

    A study published in Clinical Pharmacology and Therapeutics found that nasal administration (inhalation) of methadone provides fast action with opioid-like effects and highs. Such misuse can lead to severe methadone addiction.

    Substance abuse and addiction may cause serious long-term health challenges. Long-term side effects of methadone include damage to blood vessels, liver, and brain. It can lead to cognitive decline, heart damage, and other serious health complications.

    Other long-term effects of methadone include weight loss, nervous system disorder, and substance use disorder, which may send you to rehab.

    Methadone Abuse Can Cause Weight Loss

    Opioid addiction may cause lasting damage to food and liquid intake, resulting in metabolic alterations and eating disorders, leading to weight loss.

    Prolonged methadone causes respiratory and cardiovascular damage

    Methadone abuse can cause lasting damage to the respiratory and cardiovascular systems. Ventricular arrhythmia, coronary artery disease, and cardiomyopathy are the major side effects of liquid methadone injection.

    Injecting methadone can lead to arteriosclerosis—the hardening of arteries resulting from plaque buildup in the inner lining—and collapsed veins. Over time, these issues weaken the blood vessels, leading to aneurysms, heart attacks, strokes, and death. Moreover, extreme stress on blood vessels may increase the risk of permanent brain damage.

    High methadone doses may also block the cardiac potassium ion current and induce QT prolongation (extended interval between the heart contraction and relaxation). QT prolongation poses a risk of sudden cardiac death.

    Hardening of blood vessels leads to abnormal blood flow and poor oxygen supply, which may cause organ damage, heart attack, and more.

    Prolonged Exposure to Methadone Causes Brain Dysfunction and Death

    Physical and psychological dependence on methadone may cause addicted users to lose brain function. Studies have shown that opioids cross the blood-brain barrier, posing significant neuro cytotoxic effects.

    Therefore, repeated exposure to methadone can destroy the brain’s neurotransmitters, which causes lasting damage to the addict’s cognitive centers. Methadone side effects on the brain include violent behaviors, hallucinations, delusions, and other behavioral disorders.

    In such cases, the individuals would require addiction treatment and rehabilitation.

    Changes in Menstrual Cycle in Women and Erectile Dysfunction in Men

    Prolonged use or misuse of methadone may block the synthesis of testosterone and gonadotropin-releasing hormones in men, leading to erectile dysfunction or impotence. It may also suppress gonadotropin synthesis and release in females, leading to hormonal imbalance, amenorrhea, or anovulatory, irregular cycles.

    Development of Opiate disorder and physical dependence

    Abuse and prolonged use of methadone or any opioid can lead to opiate disorder and physical drug dependence. The feeling of euphoria experienced from opioids increases the chances that the patient may continue using even after recovery, ignoring the negative consequences.

    Opioid use disorder can result from chronic methadone abuse, leading to potential disability, relapses, and death.

    Other Side Effects of Methadone

    There are other methadone side effects with unknown or rare incidences. These include the following.

    • Bleeding gums
    • Black, tarry stools
    • Changes in skin color
    • Blood in urine or stools
    • Inability to see colors like yellow or blue.
    • Dilated neck veins
    • Skin rash
    • Tenderness
    • Weight gain
    • Darkening of skin
    • Difficulty swallowing
    • Increased thirst
    • Bulging soft spot on an infant’s head
    • Muscle pain or cramps
    • The overbright appearance of light
    • Night blindness
    • Sore tongue
    • Double vision

    Some side effects of methadone may occur that do not require medical attention since they go away as your body adjusts to the medication. Your medical provider may tell you how to prevent or reduce some side effects. Endeavor to check with your doctor if the side effects continue or become worrisome.

    Note: Methadone can also cause psychological side effects. The psychological side effects include Hallucinations, insomnia, paranoia, delusions, depression, suicidal ideations, and impaired concentration.

    You should report these issues to your doctor, who may lower your methadone dosage or switch you to a different medication.

    What Is Methadone Used For?

    Well, what is methadone used for? It is a medication commonly used for chronic pain management. Many healthcare professionals prefer methadone to other opioids due to its mild and slow action.

    Medical providers can combine methadone with other medications to treat heroin addition and opioid use disorder (OUD). Such treatment is called Methadone Maintenance, a program that utilizes methadone to treat opioid dependence.

    Methadone maintenance treatment (MMT) has proven active in treating opioid dependence since the 1950s. Opioid or heroin addicts will be given a daily (ongoing) dose of methadone as a liquid or oral pill. It helps to reduce their withdrawal symptoms and cravings for opioids.

    Although methadone is addictive, it is considerably safer than depending on illegal opioids like heroin. Patients must take methadone under medical supervision to avoid misuse. The World Health Organization (WHO) included methadone on the list of essential medicines, highlighting its importance in treating opioid dependence.

    Oral methadone has found utility as a second-line opioid treatment for cancer and a few chronic pain conditions. It is an appropriate alternative when the side effects of other opioids limit dosage increment.

    Methadone Overdose

    Overdosing is among the risks associated with methadone usage, especially in the initial stages of MMT. It is a cause for concern to physicians, especially when they have to combine methadone with other depressant drugs.

    Most overdose death cases show methadone levels that may not constitute a lethal dose but result from interaction with other medications. Methadone overdose may not be noticeable until three to four hours after ingesting, making it even more dangerous.

    Healthcare providers must closely monitor patients for signs of overdose during the first week of treatment. Methadone overdose symptoms include the following:

    • Severe chest pain and discomfort
    • Cold, clammy skin
    • Change in consciousness
    • Constricted, pinpoint pupils
    • Decreased responsiveness or awareness
    • Loss of consciousness
    • Irregular, slow, or fast heartbeat
    • Shallow, slow, or fast-breathing
    • Increased sweating
    • Coughing with pink frothy sputum
    • Swollen legs and ankles
    • Excess sedation
    • Snoring
    • Slurred speech
    • Lack of muscle tone or movement
    • Pale lips, skin, or fingernails

    Combining methadone with central nervous system depressants, such as alcohol, benzodiazepines, or other opioids, can lead to overdose, coma, or death. Physicians should inform patients of the risks of using these drugs alongside methadone.

    In case of overdose, administer Naloxone to reverse the effects of methadone. Multiple doses of Naloxone over several hours or a prolonged infusion might be necessary since methadone has a long half-life. Send overdosed patients to a hospital where professionals can monitor them for at least four hours.

    Methadone Questions and Answers

    Can you overdose on methadone?

    Yes, you can. Methadone overdose cases are prevalent due to its long half-life and the tendency to combine them with central nervous system suppressants in the initial MMT stage. You should follow your doctor’s prescription and ask questions where necessary to avoid such.

    What are methadone side effects on body?

    Methadone can cause mild to severe side effects. Common methadone side effects include nausea, vomiting, gastrointestinal discomfort, drowsiness, fainting, lightheadedness, chest pain, weight gain/loss, tiredness, and constipation. More severe ones include hallucination, respiratory depression, sexual dysfunction, tremor, addiction or substance dependence, and orthostatic hypotension.

    There’s a similar medication with less side effects – Suboxone.

    What are the side effects of liquid methadone?

    Liquid methadone is s schedule-II-controlled substance. Therefore, people can easily abuse it, become dependent, and develop addiction. Injecting liquid methadone can lead to arteriosclerosis (constriction of blood vessels) caused by plaque buildup. Asides from this, the side effects of liquid methadone are the same in other forms.

    What are methadone side effects on the brain?

    As an opioid, prolonged exposure or abuse of methadone can cross the blood-brain barrier and interfere with nervous coordination. It can cause a significant neuro cytotoxic effect, destroying the neurons and eventually leading to brain death.

    Is methadone a legally acceptable medication?

    Yes, methadone is a legally acceptable medication for chronic pain and opioid use disorder (OUD) treatment. According to the Substance Abuse and Mental Health Services Administration, Methadone is on the list of Medications for Opioid Use Disorder (MOUD).

    Who should take methadone?

    Methadone is only for people certified as suffering from chronic pains or those undergoing treatment for opioid addiction. People having mild to moderate pain should not take methadone. Patients should only take methadone under the supervision of medical professionals.


    While methadone appears milder, it remains a very potent opioid. Users and medical professionals should be careful while prescribing and administering this medication as it can pose serious health risks to patients. In extreme cases, patients may die from methadone overdose and dependence.

    Furthermore, the distribution and dispensation of methadone must be under strict legal supervision to avoid indiscriminate use or abuse.