How pain medication works

Have you ever found yourself in a pharmacy, looking for a painkiller for a headache or a pulled muscle in your back … but you don’t really know what type of painkiller to buy Download the book cover?

There are a variety of different types of pain medications available, but how exactly do they work and remember, not all of them are available over-the-counter.

What are painkillers?

  • Painkillers are medications that are used to treat or relieve pain.
  • One of the most common reasons why patients visit their doctor is for the purpose of getting relief from pain.

What are some of the different ways of providing pain relief to a patient?

  • by mouth/orally: tablets, capsules, syrups/liquids
  • by rectum: as a suppository
  • by injection: into a muscle (intra-muscular), under the skin (subcutaneous)
  • other injections: epidural, joint block injection, nerve block injection, trigger point injection
  • via a vein: usually via a drip or a PCA (patient-controlled analgesia pump, in hospital)
  • via the skin/transdermal: via a skin patch applied to the skin
  • topical: via cream, gel, patch or spray
  • miscellaneous: TENS machine, acupuncture, physiotherapy, chiropractor, yoga, pilates

What types of medication can be used to provide pain relief?

a) Paracetamol

b) NSAIDS / COXIBS (anti-inflammatories): such as aspirin, ibuprofen, diclofenac, naproxen, mefenamic acid, COXIBs

c) Opiates/opioids (also known as narcotic analgesics):
*weak opioids: codeine, dihydrocodeine
*strong opioids: morphine, oxycodone, pethidine, tramadol, pethidine

d) Combinations of paracetamol with codeine and/or other products (all in one pill/tablet)

e) Corticosteroids : such as prednisone, prednisolone, methylprednisolone

f) Anti-depressants: such as tricyclic anti-depressants, SSRI’s, SNRI’s

g) Anti-epileptic/anti-convulsant medications: such as carbamazepine, gabapentin, pregabalin

How do painkillers work to provide pain relief?

a) Paracetamol:

  • exact method by which it works is still not fully known, but it appears to block COX enzymes in the brain and spinal cord (working on parts of the brain that receive “pain signals”)
  • it offers relief of mild pain and can lower a temperature/fever
  • however, it does not have anti-inflammatory effects
  • caution must be exercised not to exceed the maximum dose of 8 (500mg) tablets per 24 hours, as overdosing can cause serious liver damage
Read  If you’re taking medication, watch what you eat and drink!


  • they reduce pain and inflammation in joints and muscles (such as in arthritis and back pain)
  • they block the effect of COX (cyclogenase enzymes), which in turn, decreases the production of prostaglandins (prostaglandins are responsible for causing pain and inflammation at the site of injury or damage)
  • they should not be used in people who are allergic to them, have peptic/stomach ulcers, chronic kidney disease, cardiac disease and in certain asthmatics as well as people with nasal polyps.
  • aspirin should never be given to a person younger than 16 years of age (risk of Reye’s syndrome)

c) Opioids:

  • they bind to opioid receptors in the brain, gut and other areas of the body
  • they are originally derived from the opium poppy plant, with morphine being the most active substance and codeine being less powerful
  • weak opioids are used to treat more severe pain that has not been relieved by paracetamol and NSAIDs/COXIBS, or they are used in combination with these medications
  • strong opioids are used to treat severe pain such as post-operative pain, cancer-related pain and pain from serious injury
  • side effects can include: nausea, vomiting, constipation, drowsiness, confusion, itching, dry mouth, breathing problems, becoming tolerant to/dependant on medication

d) Corticosteroids:

  • act as potent anti-inflammatory agents reducing redness, swelling, stiffness, itching and allergic reactions
  • side effects can include: osteoporosis, weight gain, cataract formation, headache, risk of developing type 2 diabetes, peptic ulcers, mood changes, insomnia, immune-suppression

e) Anti-depressants:

  • they work by adjusting different levels of chemicals in the brain, referred to as neurotransmitters
  • this contributes to a feeling of well-being and pain control in patients with certain chronic pain conditions that have not responded to other treatments, for example tension type headaches, PMS, fibromyalgia
  • side effects can include: blurry vision, nausea, constipation, dry mouth, headache, fatigue, difficulty urinating

f) Anti-epileptics/anti-convulsants:

  • their precise action is still unclear, but they appear to minimise the effects of nerves that cause pain
  • side effects can include: drowsiness, dizziness, nausea, fatigue