Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link



Gerald F. O’Malley

, DO, Grand Strand Regional Medical Center;

Rika O’Malley

, MD, Grand Strand Medical Center

Reviewed/Revised Dec 2022
Topic Resources

Opioids, a class of drugs derived from the opium poppy (including synthetic variations), are pain relievers with a high potential for misuse.

  • Opioids are used to relieve pain, but they also cause an exaggerated sense of well-being and, if used too much, dependence and addiction.

  • Taking too much of an opioid can be fatal, usually because breathing stops.

  • Urine tests can be done to check for opioids.

  • Treatment strategies include detoxification (stopping the drug), substitution (substituting another drug and gradually reducing its dose), and maintenance (substituting another drug that is taken indefinitely).

  • Ongoing counseling and support are essential in all treatment strategies.

"Opioid" is a term for a number of substances derived from the opium poppy and their synthetic and semisynthetic variations. Opioids have a legitimate medical use as powerful pain relievers Opioid Pain Relievers Pain relievers (analgesics) are the main drugs used to treat pain. Doctors choose a pain reliever based on the type and duration of pain and on the drug's likely benefits and risks. Most pain... read more . They include codeine (which has a low potential for dependence), oxycodone (alone and in various combinations, such as oxycodone plus acetaminophen), meperidine, morphine, pentazocine, and hydromorphone. Methadone taken by mouth and fentanyl taken by a skin patch are used for chronic severe pain. Heroin is a potent opioid that is illegal in the United States but is used in very limited treatment applications in other countries.

Abuse of opioids is relatively common, because these drugs are widely available and cause an exaggerated sense of well-being. People can become dependent on any opioid. (See also Drug Use and Abuse Overview of Substance-Related Disorders Medications and other substances, whether used for legitimate medical purposes, as a habit (for example, caffeine), or recreationally, are an integral part of everyday life for many people ... read more .)

Serious dependence and addiction rarely occur when people use opioids to treat a brief episode of severe pain (for example, from a burn or broken bone). Although many people who use opioids to relieve pain for more than several days feel some mild symptoms of opioid withdrawal when they stop, people who take opioids for a long time to treat chronic pain are at increased risk of developing a substance use disorder Substance Use Disorders Substance use disorders generally involve behavior patterns in which people continue to use a substance (for example, a recreational drug) despite having problems caused by its use. The substances... read more .

Tolerance can develop after a few days of continued opioid use. That is, people need more and more of a drug to feel the effects originally produced by a smaller amount. People may become more tolerant to some effects than to others. Although people with a substance use disorder often have tolerance to a drug, having tolerance by itself does not mean that a person has a substance use disorder.

Did You Know...

  • Taking opioids for a brief time to relieve the pain of an immediate injury, if supervised by a doctor, rarely leads to addiction.

  • Taking opioids during pregnancy can cause addiction in the fetus and withdrawal symptoms in the newborn.

Symptoms and Signs of Opioid Toxicity or Withdrawal

Opioids cause immediate and sometimes long-term symptoms.

Immediate effects

Opioids dull pain and are strong sedating drugs, causing people to become drowsy and quiet. Opioids may also cause euphoria.

Other, less desirable effects include

  • Constipation

  • Nausea and vomiting

  • Facial flushing

  • Itching

  • Confusion (especially in older people)

The products that result from the breakdown (metabolism) of the opioid meperidine can cause seizures.

When taken with certain other drugs, some opioids can cause a serious disorder called serotonin syndrome Serotonin Syndrome Serotonin syndrome is a potentially life-threatening drug reaction that tends to cause high body temperature, muscle spasms, and anxiety or delirium. Serotonin is a chemical that transmits impulses... read more . This syndrome is characterized by confusion, tremors, involuntary muscle spasms or twitching, agitation, excessive sweating, and a high body temperature.

A rare condition called spongiform leukoencephalopathy has been reported in heroin users who inhale the drug. Symptoms vary and may include motor restlessness, apathy, impaired coordination (ataxia), or paralysis. The symptoms may resolve, or they can progress to problems with the autonomic nervous system Overview of the Autonomic Nervous System The autonomic nervous system regulates certain body processes, such as blood pressure and the rate of breathing. This system works automatically (autonomously), without a person’s conscious... read more Overview of the Autonomic Nervous System and death.


Taking too much of an opioid at once (overdose) is life threatening. In the United States in 2020, there were about 91,800 deaths from opioid overdose. Breathing becomes dangerously slow and shallow and may stop. The lungs may fill with fluid. Blood pressure, heart rate, and body temperature may decrease, and pupils constrict (becoming like pinpoints). Eventually, people become unconscious or die, usually because breathing stops. Combining opioids with alcohol or other sedatives is even more lethal.

Long-term effects

Opioids themselves do not cause many long-term complications other than dependence. Some people have minor side effects such as chronic constipation, excessive sweating, sleepiness, or decreased libido. However, many complications can result from sharing needles Complications Drugs may be swallowed, smoked, inhaled through the nose as a powder (snorted), or injected. When drugs are injected, their effects may occur more quickly, be stronger, or both. Drugs may be... read more Complications with another person and from unknowingly injecting other substances with the opioid.

Withdrawal symptoms

Opioid withdrawal is uncomfortable but rarely life threatening. Symptoms can appear as early as 4 hours after opioid use stops and generally peak within 48 to 72 hours. They usually subside after about a week, although the time frame can vary considerably depending on which opioid is used.

Each opioid is eliminated from the body at a different rate, which alters how quickly withdrawal progresses and stops. Withdrawal symptoms are worse in people who have used large doses for a long time:

  • At first, people feel anxious and crave the drug.

  • Breathing becomes rapid, usually accompanied by yawning, perspiration, watery eyes, a runny nose, dilated pupils, and stomach cramps.

  • Later, people may become hyperactive and agitated and have a heightened sense of alertness.

  • Heart rate and blood pressure increase.

Other withdrawal symptoms include

  • Gooseflesh

  • Tremors

  • Muscle twitching

  • Fever and chills

  • Aching muscles

  • Loss of appetite

  • Nausea and vomiting

  • Diarrhea

Opioid use during pregnancy is especially serious because heroin and methadone easily cross the placenta and affect the fetus (see How Drugs Cross the Placenta How Drugs Cross the Placenta How Drugs Cross the Placenta ). Because babies born to women who use opioids have been exposed to the drugs their mothers have taken, they may quickly develop withdrawal symptoms, including

  • Tremors

  • High-pitched crying

  • Jitters

  • Seizures

  • Rapid breathing

If mothers take opioids immediately before labor and delivery, the baby’s breathing may be weak.

Diagnosis of Opioid Toxicity or Withdrawal

  • A doctor's evaluation

  • Sometimes urine tests

Acute opioid intoxication is usually apparent based on what people or their friends tell the doctor and on results of the physical examination. If it is not clear why a person is acting abnormally, doctors may do tests to rule out other possible causes of symptoms, such as a low blood sugar level Hypoglycemia Hypoglycemia is abnormally low levels of sugar (glucose) in the blood. Hypoglycemia is most often caused by medications taken to control diabetes. Much less common causes of hypoglycemia include... read more or a head injury Overview of Head Injuries Head injuries that involve the brain are particularly concerning. Common causes of head injuries include falls, motor vehicle crashes, assaults, and mishaps during sports and recreational activities... read more . Doctors can also do urine tests to check for the drug. Other tests may be done to check for complications.

Treatment of Opioid Toxicity or Withdrawal

An opioid overdose requires emergency treatment, but the ultimate and difficult goal of treatment is to help people control their use of opioids. Treatment can include

  • Emergency treatment

  • Detoxification

  • Possible maintenance treatment (for people who are unable to quit)

  • Rehabilitation

Emergency treatment

An opioid overdose is a medical emergency that must be treated quickly to prevent death. Breathing may require support, sometimes with a ventilator Mechanical Ventilation Mechanical ventilation is use of a machine to aid the movement of air into and out of the lungs. Some people with respiratory failure need a mechanical ventilator (a machine that helps air get... read more , if the overdose has suppressed breathing.

A medication called naloxone is given as an antidote to the opioid, rapidly reversing all adverse effects. It is given by injection or by nasal spray. Because some people briefly become agitated and delirious before they become fully conscious, physical restraints may be applied for a short time. Because naloxone precipitates withdrawal symptoms in people who are dependent on opioids, it is used only when necessary (as when breathing is weak).

People recovering from an overdose should be observed for several hours until the effects of naloxone have worn off to be sure that no side effects of the opioid remain. If people took an opioid with long-lasting effects (such as methadone or slow-release forms of other opioids), they are usually observed for a longer time.

If symptoms redevelop, people may be given another dose of naloxone, be admitted to the hospital, or both.


There are several approaches to detoxification:

  • Stopping the opioid and allowing withdrawal to run its course (cold turkey detoxification)

  • Substituting a similar but less potent drug, then gradually decreasing the dose and stopping the drug

In both detoxification strategies, treatment is usually needed to lessen the symptoms of withdrawal. The medication clonidine usually provides some relief. However, clonidine may cause side effects, such as low blood pressure Low Blood Pressure Low blood pressure is blood pressure low enough to cause symptoms such as dizziness and fainting. Very low blood pressure can cause damage to organs, a process called shock. Various drugs and... read more and drowsiness. Stopping clonidine may itself cause withdrawal symptoms, such as restlessness, insomnia, irritability, a fast heartbeat, and headaches.

Substitution typically involves giving drugs such as methadone and buprenorphine, which are then slowly decreased and eventually stopped completely.

Detoxification must be followed by rehabilitation Rehabilitation Opioids, a class of drugs derived from the opium poppy (including synthetic variations), are pain relievers with a high potential for misuse. Opioids are used to relieve pain, but they also... read more to prevent a return to opioid use. Ongoing treatment may include long-term counseling and support and medications such as naltrexone.

Maintenance treatment

For people who continually return to using opioids (called opioid use disorder), another approach—called maintenance—is often preferred. It involves substituting a prescribed medication at a regular dose that the user takes for a long time (months or years) rather than decreasing the dose and eventually stopping the medication. Methadone, buprenorphine, or naltrexone may be used as substitutes for opioids.

Maintaining opioid users with regular doses of one of these medications enables them to be socially productive because they do not have to spend time getting the illicit opioid and because the medications used do not interfere with functioning the way that illicit drug use does. For some opioid users, the treatment works. For many, lifelong maintenance is necessary.

Methadone suppresses withdrawal symptoms and the craving for the opioid without making opioid users overly drowsy or elated. However, opioid users must appear once a day at a clinic where methadone is dispensed in the amount that prevents severe withdrawal symptoms, minimizes craving, and supports daily functioning.

Buprenorphine is being used more and more because it can be prescribed by doctors in their office. Thus, opioid users do not have to go to a special clinic.

Naltrexone is a medication that blocks the effects of opioids (opioid antagonist). Before starting naltrexone, people must be fully detoxified from opioids, or a severe withdrawal reaction can occur. Depending on the dose, naltrexone’s effects last from 24 to 72 hours. Thus, the medication can be taken once a day or as few as 3 times a week. Because this medication has no opioid effects, naltrexone is most useful for opioid users who are strongly motivated to remain free of opioids and who are not severely dependent on opioids.


Regardless of which approach is used, ongoing counseling and support is essential. Support may include specially trained doctors, nurses, counselors, opioid maintenance programs, family members, friends, and other people with the same substance use disorder (support groups).

The therapeutic community concept emerged nearly 25 years ago in response to the problems of heroin use. Samaritan Daytop Village and Phoenix House pioneered this nondrug approach. Opioid users live in a communal, residential center for an extended period of time. These programs help people build new lives through training, education, and redirection. The programs have helped many people, but initial dropout rates are high.

Questions about precisely how well these programs have worked and how widely they should be applied remain unanswered. Because these programs require a lot of resources to run, many people may be unable to afford them.

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

  • National Institute on Drug Abuse (NIDA): Opioid-specific information from the federal agency that supports scientific research into drug use and its consequences and supplies information about commonly used drugs, research priorities and progress, clinical resources, and grant and funding opportunities.

  • Phoenix House: Residential substance use disorder treatment in states and Washington, DC.

  • Samaritan Daytop Village: A New York-based agency that helps various populations struggling with addictions, including military veterans, mothers and babies, and homeless people.

  • Substance Abuse and Mental Health Services Administration (SAMHSA): US Department of Health agency that leads public health efforts to improve behavioral health and provides resources, including treatment locators, toll-free helplines, practitioner training tools, statistics, and publications on a variety of substance-related topics.

Drugs Mentioned In This Article

Generic Name Select Brand Names
No brand name available
Dazidox , Endocodone , ETH-Oxydose, Oxaydo, OXECTA, OxyContin, Oxydose , OxyFast, OxyIR, Percolone, Roxicodone, Roxybond, XTAMPZA
7T Gummy ES, Acephen, Aceta, Actamin, Adult Pain Relief, Anacin Aspirin Free, Aphen, Apra, Children's Acetaminophen, Children's Pain & Fever , Children's Pain Relief, Comtrex Sore Throat Relief, ED-APAP, ElixSure Fever/Pain, Feverall, Genapap, Genebs, Goody's Back & Body Pain, Infantaire, Infants' Acetaminophen, LIQUID PAIN RELIEF, Little Fevers, Little Remedies Infant Fever + Pain Reliever, Mapap, Mapap Arthritis Pain, Mapap Infants, Mapap Junior, M-PAP, Nortemp, Ofirmev, Pain & Fever , Pain and Fever , PAIN RELIEF , PAIN RELIEF Extra Strength, Panadol, PediaCare Children's Fever Reducer/Pain Reliever, PediaCare Children's Smooth Metls Fever Reducer/Pain Reliever, PediaCare Infant's Fever Reducer/Pain Reliever, Pediaphen, PHARBETOL, Plus PHARMA, Q-Pap, Q-Pap Extra Strength, Silapap, Triaminic Fever Reducer and Pain Reliever, Triaminic Infant Fever Reducer and Pain Reliever, Tylenol, Tylenol 8 Hour, Tylenol 8 Hour Arthritis Pain, Tylenol 8 Hour Muscle Aches & Pain, Tylenol Arthritis Pain, Tylenol Children's, Tylenol Children's Pain+Fever, Tylenol CrushableTablet, Tylenol Extra Strength, Tylenol Infants', Tylenol Infants Pain + Fever, Tylenol Junior Strength, Tylenol Pain + Fever, Tylenol Regular Strength, Tylenol Sore Throat, XS No Aspirin, XS Pain Reliever
Demerol, Meperitab
ARYMO ER, Astramorph PF, Avinza, DepoDur, Duramorph PF, Infumorph, Kadian, MITIGO, MORPHABOND, MS Contin, MSIR, Opium Tincture, Oramorph SR, RMS, Roxanol, Roxanol-T
Dilaudid, Dilaudid-HP, Exalgo, Palladone, Simplist Dilaudid
Dolophine, Methadose
ABSTRAL, Actiq, Duragesic, Fentora, IONSYS, Lazanda, Onsolis, Sublimaze, SUBSYS
EVZIO, Kloxxado, Narcan, ZIMHI
Catapres, Catapres-TTS, Duraclon, Kapvay, NEXICLON XR
Belbuca, Brixadi, Buprenex, Butrans, Probuphine, Sublocade, Subutex
Depade, ReVia, Vivitrol
quiz link

Test your knowledge

Take a Quiz!