Drugs of varying potency that are used to relieve pain

Common drugs

    Opioid painkillers

  • Codeine

  • Diamorphine

  • Fentanyl

  • Methadone

  • Morphine

  • Pentazocine

  • Pethidine

  • Tramadol

    Nonopioid painkillers

  • Aspirin

  • Celecoxib

  • Diclofenac

  • Etodolac

  • Etoricoxib

  • Fenoprofen

  • Ibuprofen

  • Indometacin

  • Ketoprofen

  • Mefenamic acid

  • Naproxen

  • Paracetamol

  • Piroxicam

  • Piroxicam

    Combination painkillers

  • Aspirin with codeine

  • Dextropropoxyphene with paracetamol

  • Dihydrocodeine with paracetamol

  • Ibuprofen with codeine

  • Paracetamol with codeine

Painkillers work in different ways, depending on the type of preparation. Some drugs block the nerve pathways that transmit pain signals from a part of the body to the brain. Other painkillers reduce the perception of pain by preventing further transmission of pain signals once they reach the brain. However, pain relief for most long-term disorders depends on treatment of the underlying cause.

What are the types?

The two main types of painkiller are opioid (narcotic) and nonopioid (non-narcotic). A number of commonly used painkillers are combinations of more than one drug. Opioid painkillers are mainly used to relieve severe pain. Nonopioid painkillers, most of which are nonsteroidal anti-inflammatory drugs, may be used to ease mild to moderate pain. Combinations of two or more painkillers and, in some cases, another drug may provide greater pain relief than a single drug.

Opioid painkillers

These drugs are the strongest painkillers available. They may be given for pain during a heart attack (see Myocardial infarction) or following surgery or serious injury. They are also widely used in pain relief for cancer. Opioids act on the brain, altering the perception of pain. These drugs work in a similar way to natural substances called endorphins, which are released in the brain in response to pain. Opioids bind to the same receptors in the brain as endorphins and stop the transmission of pain signals from cell to cell (see How opioid painkillers work).

Prolonged use of opioids may lead to dependence. However, you are very unlikely to become dependent if you take the drugs for a few days to relieve severe pain. Dependence is also not usually a cause for concern in the treatment of pain in a terminally ill person. However, prolonged use leads to tolerance, which means that progressively higher doses are needed to achieve the same level of pain relief.

Opioids may be taken orally or, if the pain is extremely severe or accompanied by vomiting, may be given by injection. They are also available as patches. Side effects include constipation, nausea, vomiting, and drowsiness. Larger doses can depress breathing and may also cause confusion and impaired consciousness. Overdose may be fatal.

Nonopioid painkillers

These types of drug are less potent than opioids, and a number are available over the counter. They include paracetamol and non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin and ibuprofen. Nonopioids are used mainly for pain such as headache or menstrual pain and also lower fever and reduce inflammation in conditions such as arthritis.

Side effects are rarely a problem if you take nonopioid painkillers occasionally and at the doses recommended for pain relief. However, when used repeatedly, aspirin and other NSAIDs may damage the lining of the stomach and intestines. NSAIDs may also cause various other adverse effects; for a fuller discussion of these effects, and warning about use of NSAIDs.

Paracetamol relieves pain and lowers fever, but, unlike NSAIDs, it does not reduce inflammation. The drug works by blocking pain impulses in the brain. Paracetamol is dangerous if taken in doses above the recommended maximum daily intake. Overdose can cause severe liver and kidney damage.

Combination painkillers

Combination painkillers, which may contain other, non-painkiller types of drug, are available as over-the-counter remedies for headaches, backache, menstrual pain, and other minor disorders. However, caffeine, an ingredient included in some remedies, may itself cause headaches.


Do not give aspirin to children under 16 years, except on the advice of a doctor, because it increases the risk of Reye’s syndrome.

Drug Action: How Opioid Painkillers Work

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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