Skip to Content

Chronic Pain


James C. Watson

, MD, Mayo Clinic College of Medicine and Science

Last full review/revision Feb 2020| Content last modified Feb 2020

Chronic pain is pain that persists or recurs for > 3 months, persists > 1 month after resolution of an acute tissue injury, or accompanies a nonhealing lesion. Causes include chronic disorders (eg, cancer, arthritis, diabetes), injuries (eg, herniated disk, torn ligament), and many primary pain disorders (eg, neuropathic pain, fibromyalgia, chronic headache). Various drugs and psychologic treatments are used.

(See also Fibromyalgia and Overview of Pain.)

Unresolved, long-lasting disorders (eg, cancer, rheumatoid arthritis, herniated disk) that produce ongoing nociceptive stimuli may account completely for chronic pain. Alternatively, injury, even mild injury, may lead to long-lasting changes (sensitization) in the nervous system—from peripheral receptors to the cerebral cortex—that may produce persistent pain in the absence of ongoing nociceptive stimuli. With sensitization, discomfort that is due to a nearly resolved disorder and might otherwise be perceived as mild or trivial is instead perceived as significant pain.

Psychologic factors may also amplify persistent pain. Thus, chronic pain commonly appears out of proportion to identifiable physical processes.

In some cases (eg, chronic back pain after injury), the original precipitant of pain is obvious; in others (eg, chronic headache, atypical facial pain, chronic abdominal pain), the precipitant is remote or occult.

In most patients, physical processes are undeniably involved in sustaining chronic pain and are sometimes the main factor (eg, in cancer pain). However, even in these patients, psychologic factors usually also play a role. Patients who have to continually prove that they are sick to obtain medical care, insurance coverage, or work relief may unconsciously reinforce their pain perceptions, particularly when litigation is involved. This response differs from malingering, which is conscious exaggeration of symptoms for secondary gain (eg, time off, disability payments).

Various factors in the patient’s environment (eg, family members, friends) may reinforce behaviors that perpetuate chronic pain.

Chronic pain can lead to or exacerbate psychologic problems (eg, depression, anxiety). Distinguishing psychologic cause from effect is often difficult.

Symptoms and Signs of Chronic Pain

Chronic pain often leads to vegetative signs (eg, lassitude, sleep disturbance, decreased appetite, loss of taste for food, weight loss, diminished libido, constipation), which develop gradually. Constant, unremitting pain may lead to depression and anxiety and interfere with almost all activities. Patients may become inactive, withdraw socially, and become preoccupied with physical health. Psychologic and social impairment may be severe, causing virtual lack of function.

Some patients, particularly those without a clear-cut ongoing cause, have a history of failed medical and surgical treatments, multiple (and duplicative) diagnostic tests, use of many drugs (sometimes involving abuse or addiction), and inappropriate use of health care.

Diagnosis of Chronic Pain

  • Evaluation for physical cause initially and if symptoms change

A physical cause of chronic pain should always be sought—even if a prominent psychologic contribution to the pain is likely. Physical processes associated with the pain should be evaluated appropriately and characterized. However, once a full evaluation is done, repeating tests in the absence of new findings is not useful. The best approach is often to stop testing and focus on relieving pain and restoring function.

The effect of pain on the patient’s life should be evaluated; evaluation by an occupational therapist may be necessary. Formal psychiatric evaluation should be considered if a coexisting psychiatric disorder (eg, major depression, an anxiety disorder) is suspected as cause or effect. Pain relief and functional improvement are unlikely if concomitant psychiatric disorders are not managed.

Treatment of Chronic Pain

  • Often multimodal therapy (eg, analgesics, physical methods, psychologic treatments)

Specific causes of chronic pain should be treated. Early, aggressive treatment of acute pain is always preferable and may limit or prevent sensitization and remodeling and hence prevent progression to chronic pain.

Drugs or physical methods may be used. Psychologic and behavioral treatments are usually helpful. Many patients who have marked functional impairment or who do not respond to a reasonable attempt at management by their physician benefit from the multidisciplinary approach available at a pain clinic.

Many patients prefer to have their pain treated at home, even though an institution may offer more advanced modalities of pain management. Also, pain control may be compromised by certain practices in institutions; for example, they restrict visiting hours, use of televisions and radios (which provide useful distraction), and use of heating pads (for fear of thermal injury).


Analgesics include

  • Nonsteroidal anti-inflammatory drugs (NSAIDs)
  • Opioid analgesics
  • Adjuvant analgesics (eg, antidepressants, antiseizure drugs—see table Drugs for Neuropathic Pain)

Use of one or more drugs with different mechanisms of action (rational polypharmacy) is often necessary for chronic pain. Adjuvant analgesics are most commonly used for neuropathic pain.

Opioid analgesics are useful in managing chronic pain due to cancer or other terminal disorders. Opioids are sometimes underused in patients with such disorders, resulting in needless pain and suffering.

Reasons for undertreatment include

  • Underestimation of the effective dose
  • Overestimation of the risk of adverse effects

Generally, opioids should not be withheld when treating cancer pain or other terminal disorders; in such cases, adverse effects can be prevented or managed, and addiction is less of a concern.

Nondrug and nonopioid drug treatments are generally preferred to opioid treatment for chronic pain that is not due to cancer or another terminal disorder. The Centers for Disease Control and Prevention (CDC) has published guidelines for prescribing opioids for chronic pain. However, for persistent, moderate-to-severe pain that impairs function, opioids may be considered, usually as adjunctive therapy, when potential benefits are expected to exceed risks. Factors to consider include the following:

  • What conventional treatment practice is
  • Whether other treatments are reasonable
  • Whether the patient has an unusually high risk of adverse effects from an opioid
  • Whether the patient is at risk of misuse, diversion, or abuse (aberrant drug-taking behaviors)

When prescribing opioids for chronic pain, physicians should take several steps:

  • Provide education and counseling about misuse: Topics should include the risks of combining opioids with alcohol and anxiolytics and of self-adjusting dosing and the need for safe, secure storage of drugs. Patients should also be taught how to correctly dispose of unused drugs; they should be instructed not to share opioids and to contact their physician if they experience sedation.
  • Evaluate patients for risk of misuse, diversion, and abuse: Risk factors include prior or current alcohol or drug abuse, a family history of alcohol or drug abuse, and a prior or current major psychiatric disorder. The patient's history of controlled substance use should be reviewed using information from state prescription drug monitoring programs (PDMPs). Current recommendations are to screen with the PDMP when prescribing opioids initially and when refilling each prescription or at least every 3 months. Presence of risk factors does not always contraindicate opioid use. However, if patients have risk factors, they should be referred to a pain management specialist, or the physician should take special precautions to deter misuse, diversion, and abuse; these measures can include prescribing only small amounts (requiring frequent visits for refills), not refilling prescriptions allegedly lost, and using urine drug screening before first prescribing opioids and periodically (eg, at least yearly) thereafter to confirm that the prescribed opioid is being taken and not diverted to others.
  • Prescribe buprenorphine or methadone only if trained in the unique qualities and risks of these drugs.
  • Consider prescribing naloxone if patients are at risk of overdose but still require opioid therapy: Clinicians should discuss the risks of overdose and respiratory depression with the patient and family members. Risk factors for overdose include comorbidities, unavoidable concomitant drug usage (eg, benzodiazepines), prior history of overdose or substance use disorder, and use of high-dose opioids (≥ 50 oral morphine milligram equivalents daily [OMME]).
  • Obtain informed consent, when possible, to help clarify the goals, expectations, and risks of treatment, as well as the possible use of nonopioid treatment alternatives.
  • Regularly reassess the extent of pain reduction, functional improvement, and adverse effects, and look for signs suggesting misuse, diversion, or abuse: For example, reassess patients within 4 weeks of starting opioids, when the dose is increased, and at least every 3 months.
  • Reassess potential benefits and risks if opioid dose exceeds 50 mg OMME/day, and avoid exceeding 90 mg OMME/day when possible.

Previously, long-acting opioids were long preferred to immediate-release opioids in the treatment of chronic pain; however, doses of long-acting opioids are often higher, and they may have more adverse effects. Current guidelines emphasize that when starting opioids for chronic pain, clinicians should prescribe immediate-release opioids instead of long-acting opioids (1). Also, using the lowest effective dose (even for immediate-release opioids) is preferred over transitioning to a long-acting opioid (see tables Opioid Analgesics and Equianalgesic Doses of Opioid Analgesics).

Equianalgesic Doses of Opioid Analgesics*


Parenteral (mg)

Oral (mg)
































* Equivalences are based on single-dose studies influenced by clinical experience. Cross-tolerance between drugs is incomplete, so when one drug is substituted for another, the equianalgesic dose should be reduced by 50%; methadone should be reduced by 75–90%. Some experts have suggested that morphine:methadone equivalence is nonlinear and that it changes when morphine dosage is higher, as in the following morphine-to-methadone conversion ratios:

  • < 100 OMME/day: 3:1
  • 101–300 OMME/day: 5:1
  • 301–600 OMME/day: 10:1
  • 601–800 OMME/day: 12:1
  • 801–1000 OMME/day: 15:1
  • ≥ 1001 OMME/day: 20:1

Methadone dosage should still be reduced by 75–90% even when this more conservative equivalence calculation is used.

† Parental oxycodone is available in Europe but not in the US.

OMME = oral morphine milligram equivalents.

As pain lessens, patients usually need help reducing use of opioids. If depression coexists with pain, antidepressants should be used.

Depending on the condition, joint or spinal injections, nerve blocks, neuromodulation (spinal cord stimulation) or neuraxial infusion may be appropriate.

Physical methods

Many patients benefit from physical therapy or occupational therapy. Spray-and-stretch techniques can relieve myofascial trigger points. Some patients require an orthosis.

Spinal cord stimulation may be appropriate.

Transcutaneous electrical nerve stimulation (TENS) uses low current at low-frequency oscillation to help manage pain.

Integrative medicine techniques

Integrative medicine techniques (previously called complementary alternative medicine) can often be used to treat chronic pain. Techniques include acupuncture, mind-body techniques (eg, meditation, yoga, tai chi), manipulation and body-based therapies (eg, chiropractic or osteopathic manipulation, massage therapy), and energy-based therapies (eg, therapeutic touch, reiki).

Psychologic treatments

Behavioral treatments can improve patient function, even without reducing pain. Patients should keep a diary of daily activities to pinpoint areas amenable to change. The physician should make specific recommendations for gradually increasing physical activity and social engagement. Activities should be prescribed in gradually increasing units of time; pain should not, if at all possible, be allowed to abort the commitment to greater function. When activities are increased in this way, reports of pain often decrease.

Various cognitive-behavioral techniques of pain control (eg, relaxation training, distraction techniques, hypnosis, biofeedback) may be useful. Patients may be taught to use distraction by guided imagery (organized fantasy evoking calm and comfort—eg, imagining resting on a beach or lying in a hammock). Other cognitive-behavioral techniques (eg, self-hypnosis) may require training by specialists.

Behavior of family members or fellow workers that reinforces pain behavior (eg, constant inquiries about the patient’s health or insistence that the patient do no chores) should be discouraged. The physician should avoid reinforcing pain behavior, discourage maladaptive behaviors, applaud progress, and provide pain treatment while emphasizing return of function.

Pain rehabilitation programs

Pain rehabilitation programs are multidisciplinary programs for patients with chronic pain. These programs include education. cognitive-behavioral therapy, physical therapy, drug regimen simplification, and sometimes detoxification and tapering of analgesics. They focus on

  • Restoring function
  • Improving quality of life
  • Helping patients control their own life, despite chronic pain

Treatment reference

  • 1. Centers for Disease Control and Prevention: 2018 Annual surveillance report of drug-related risks and outcomes—United States. Surveillance special report. Centers for Disease Control and Prevention, U.S. Department of Health and Human Services. Published August 31, 2018. Accessed 1/22/20.

Key Points

  • Nociceptive stimuli, sensitization of the nervous system, and psychologic factors can contribute to chronic pain.
  • Distinguishing between the psychologic causes and effects of chronic pain may be difficult.
  • Seek a physical cause even if psychologic factors are prominent, and always evaluate the effect of pain on the patient's life.
  • Treat poorly controlled pain with multimodal therapy (eg, appropriate physical, psychologic, behavioral, and interventional treatments; drugs).

More Information

  • CDC guideline for prescribing opioids for chronic pain

Drugs Mentioned In This Article

Drug Name Select Trade
Hydromorphone DILAUDID
buprenorphine BUPRENEX
Levorphanol No US brand name
Pentazocine TALWIN
Meperidine DEMEROL
methadone DOLOPHINE
naloxone EVZIO

Copyright © 2022 Merck & Co., Inc., known as MSD outside of the US, Kenilworth, New Jersey, USA. All rights reserved. Merck Manual Disclaimer