Pain Relief Medications

What are pain medications?

Pain is the oldest complaint that medicine has attempted to treat, and there are thousands of different ways to reduce pain with chemicals. Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.

Pain medications (also called analgesics or pain relievers) are a class of drugs used to relieve pain. Analgesics lessen the amount, duration, or sensation of pain. They work by reducing the pain by interfering with the way the pain message is transmitted by the nerves. Pain relievers do not treat the problem causing the pain, but they provide temporary relief from pain symptoms.

Analgesics are used to treat pain related to many conditions, including the following:

  • arthritis and joint pain
  • headaches
  • muscular aches
  • menstrual cramps
  • back pain (including herniated discs, degenerative disc disease and spinal stenosis)
  • trauma pain
  • childbirth pain
  • surgical pain
  • orofacial and dental pain
  • fibromyalgia
  • colds and flu

Pain relievers work at the level of the nerves, either by blocking the signal from the peripheral nervous system, or by distorting the interpretation by the central nervous system. Selection of an appropriate analgesic is based on consideration of the risk-benefit factors of each class of drugs, based on type of pain, severity of pain, and risk of adverse effects. Each pain medication has its advantages and risks. Specific types of pain may respond better to one kind of medication than to another kind. Each person may have a slightly different response to a pain medication.

Types of pain medications range from the gentle over-the-counter acetaminophen to the very strong and highly addictive narcotics. Medications within classes function differently. Some are more useful than the others, depending on the person and the type of pain.


Acetaminophen (Tylenol) is a pain reliever and fever reducer with no anti-inflammatory properties. It relieves pain by working centrally (in the brain) to elevate the pain threshold and thus switching off the perception of pain. It is appropriate for mild to moderate pain. Acetaminophen has very few side effects and is relatively inexpensive. It is less irritating to the stomach than other over-the-counter pain medications and is safer for children. However, the risk of liver or kidney damage is significant when acetaminophen is used at high doses.

Acetaminophen does not produce addiction, tolerance, or gastrointestinal (stomach) upset. Very few patients are allergic to it.

Non-steroidal anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs (NSAIDs) represent a widely used group of pain relievers. Drugs in this class have varying degrees of anti-inflammatory, antipyretic, and analgesic properties as well as different side effects, time to onset of action, and duration of action.

NSAIDs stop cyclooxygenase enzymes (also called COX enzymes) in the body from working. COX enzymes speed up the body's production of hormone-like substances called prostaglandins. Prostaglandins cause the feeling of pain by irritating the nerve endings. They are also part of the system that helps the body control its temperature. By inhibiting COX enzymes and as a consequence by reducing the level of prostaglandins, NSAIDs help relieve pain. They also help reduce inflammation (swelling), lower fevers and prevent blood from clotting.

NSAIDs are used primarily to treat inflammation, mild to moderate pain, and fever. Aspirin is used to inhibit the clotting of blood and prevent strokes and heart attacks in individuals at high risk.

NSAIDs are used to relieve pain related to the following conditions:

  • arthritis, osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, gout, pseudogout, psoriatic arthritis, juvenile arthritis
  • muscle sprains and strains
  • minor injuries and trauma pain (e.g. sports injuries)
  • headaches, migraines
  • eye and ear pain
  • toothaches and other types of dental pain, orofacial pain
  • neck pain, including whiplash
  • back pain, including back sprain, degenerative disc disease, herniated disc, sciatica and spinal stenosis
  • shoulder pain
  • arm and wrist pain, including tennis elbow and carpal tunnel syndrome
  • menstrual cramps, pelvic pain
  • leg pain, knee pain and foot pain
  • joint pain
  • chronic fatigue syndrome
  • complex regional pain syndrome
  • fibromyalgia

Like acetaminophen, they are relatively inexpensive. However, NSAIDs are usually not appropriate for people with stomach problems because they may have a higher risk for stomach bleeding. All NSAIDs except aspirin increase the risk of serious adverse cardiovascular events, such as heart attack or stroke. NSAIDs can also interfere with other medications.

Common side effects include: upset stomach, nausea, abdominal pain, diarrhea, heartburn, unusual bleeding, drowsiness, dizziness, skin rashes. More severe side effects include: allergic reactions, high blood pressure, stomach bleeding, stomach ulcers (with long-term use), kidney or liver problems.

Widely used NSAIDs include: ibuprofen, ketoprofen, naproxen, diclofenac, and ketorolac.

Most NSAIDs are appropriate only for oral administration. However ketorolac (Toradol) is appropriate for injection and may be used in moderate to severe pain for short periods. Ketorolac has the distinction of being the only non-narcotic pain reliever available in a parenteral formulation.

COX-2 inhibitors

COX-2 inhibitors (Coxibs) are a relatively new type of prescription NSAIDs that reduces pain and inflammation by blocking a specific enzyme (COX-2) in the body. These medications target only the COX-2 enzyme that stimulates the inflammatory response. Because they do not block the actions of the COX-1 enzyme, these medications generally don't cause the kind of stomach upset or bleeding that traditional NSAIDs do. COX-2 inhibitors also don't offer the same kind of protection against heart disease.

Currently, only celecoxib (Celebrex) remains on the market. Valdecoxib (Bextra) and rofecoxib (Vioxx) have been voluntarily withdrawn from the market by their manufacturers because of an increased risk of heart attack, stroke, and severe skin toxicity.

COX-2 inhibitors are prescribed for osteoarthritis, rheumatoid arthritis and some types of acute pain. Coxibs are often more expensive than other NSAIDs.

Narcotic analgesics

Narcotic medications contain natural, synthetic or semi-synthetic opiates (natural opium alkaloids). Narcotic analgesics act directly on the central nervous system. They have a higher analgesic potency and wider range of indications than any of the other currently available medications for pain control. They are used to relieve moderate to severe pain and are often prescribed to patients recovering from operations and serious injuries.

Narcotic analgesics differ in their potency, speed of onset, duration of action, and route of administration. Commonly used narcotics, listed in ascending order of potency include: codeine (Tylenol #3), propoxyphene (Darvocet), hydrocodone (Vicodin), oxycodone (Percocet, Oxycontin). The most potent opioids are fentanyl (Sublimaze), hydromorphone (Dilaudid), meperidine (Demerol), morphine, oxymorphone (Numorphan).

Narcotics act by attaching to specific proteins called opioid receptors, which are found in the brain, spinal cord, and gastrointestinal tract. When these compounds attach to certain opioid receptors in the brain and spinal cord, they can effectively change the way a person experiences pain. They inhibit pain-transmitting neurons and stimulate pain-inhibitory neurons thus changing the brainís interpretation of pain.

Long-term use of narcotic analgesics can lead to physical dependence - the body adapts to the presence of the substance and withdrawal symptoms occur if use is reduced abruptly. This can also include tolerance, which means that higher doses of a medication must be taken to obtain the same initial effects. Physical dependence is not the same as addiction. Physical dependence can occur even with appropriate long-term use of opioid and other medications. Addiction is a compulsive, often uncontrollable drug use in spite of negative consequences.

Narcotic pain relievers have several side effects and potential risks, such as impairment of mental function, drowsiness, dizziness, constipation, nausea, vomiting, dry mouth, sedation. Patients taking a narcotic should avoid driving or operating heavy machinery. Addiction to narcotics is a possible, but unlikely, event. It is rare for people to become addicted if the drugs are used to treat pain for a short period of time. Studies have shown that properly managed medical use of narcotic analgesics is safe and rarely causes addiction. Taken exactly as prescribed, they can be used to manage pain effectively.

Despite significant side effects, narcotic analgesics remain the most potent and effective pain relievers available today.

Combined analgesics

Compound or combined analgesics usually contain a small amount of a mild narcotic, and a simple analgesic such as aspirin or paracetamol. These combination analgesics are often prescribed if the non-narcotic painkillers are not enough. People who experience migraines may use combination analgesics. Some combination analgesics are: Aspirin with codeine, Dextropropoxyphene with paracetamol, Dihydrocodeine with paracetamol, Paracetamol with codeine.

Adjuvant analgesics

Adjuvant analgesics are not analgesics in the true pharmacological sense, but may contribute significantly to pain relief in selected circumstances when used either alone or in combination with other analgesics.

More information about Adjuvant analgesics


Antidepressants may be considered multipurpose analgesics, appropriate for a trial in any persistent pain condition. Analgesic effect occurs at lower doses and more quickly than antidepressant effects.

Tricyclic antidepressants (TCAs) such as amitriptyline, nortriptyline and desipramine are successfully used in migraine, diabetic peripheral neuropathy, post-herpetic neuralgia (PHN), arthritis pain and post-stroke pain.

TCAs are more effective at relieving pain than the newer antidepressants, but have double the rate of adverse effects.


Anticonvulsants are commonly used to manage neuropathic pain. Although these drugs have been used for decades, their widespread use for pain did not begin until several years after the FDA approval of gabapentin (Neurontin).

Gabapentin and pregabalin are used for the treatment of diabetic painful polyneuropathy and postherpetic neuralgia. Phenytoin, carbamazepine, valproic acid, lamotrigine, topiramate, and oxcarbazepine, also are used in neuropathic pain.

Muscle relaxants

Skeletal muscle relaxants relieve pain from muscle spasms by promoting relaxation and depressing the nervous system.

Local anesthetics

Local anesthetics may provide relief of neuropathic pain if neither antidepressants nor anticonvulsants are effective. Topical 5% lidocaine gel (Lidoderm) has modest effectiveness in postherpetic neuralgia.

References & Resources

  • 1. The Merck Manual of Medical Information. Mark H. Beers et al., eds. 2nd Home Edition. Whitehouse Station, NJ: Merck; 2003.
  • 2. Pain medications MedlinePlus Medical Encyclopedia. U.S. National Library of Medicine
  • 3. Physicians' Desk Reference. 59th ed. Montvale, N.J.: Thomson PDR, 2005.

Published: May 05, 2007
Last updated: April 18, 2018


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