The opioids work on specific opioid receptors in the body, which are mainly located in the brain and the spinal cord. Many oral opioids are used in the treatment of chronic pain. Combining opioids with other painkillers such as paracetamol and NSAIDs involves attacking the pain on different receptors. This often decreases your opioid requirements by up to 30 percent, which leads to improved pain relief and a reduced risk of side effects.

Well-known examples of opioids are codeine, morphine and pethidine.

They can be categorised according to their effect in:

Low-efficacy opioids (examples include codeine (codeine phosphate) and propoxyfene).They are effective against mild to moderate pain, but scientific studies have shown that paracetamol and NSAIDs in optimal doses are more effective. If paracetamol with or without an NSAID does not relieve your pain sufficiently, you will benefit by adding codeine or propoxyfene to your medication. Many manufacturers combine these different painkillers in one commercial preparation and aim to block pain at two or three different receptor sites with one tablet (e.g. Myprodol® : paracetamol + ibuprofen + codeine; Doxyfene® : paracetamol + propoxyfene). Like all the opioids, codeine and propoxyphene might cause sedation. Codeine is also a good cough suppressant, even at lower doses than used for pain relief.

Moderate-efficacy opioids

These include dihydrocodeine (e.g. DF118®), tilidine (DF118n®) and tramadol (Tramal®). They are effective against moderate pain, and in adequate doses also against more severe pain. They can be taken orally. Tramadol causes less sedation and respiratory depression. None of these agents should be taken together with other central nervous system depressants like sleeping tablets, sedatives, or even alcohol.

High-efficacy opioids

Examples of strong opioids are morphine and pethidine. They are effective against severe pain and are mostly administered by injection. An interesting finding after surgery is that strong opioids do not seem to take ordinary headaches away, whereas simple paracetamol does.

The side effects differ in severity between the different preparations, but generally affect one’s mental state: drowsiness, decreased alertness (take care when driving a car), sedation (or sometimes agitation, especially in children), euphoria or dysphoria (e.g. some patients report that it feels as if their body does not belong to them anymore), dependence and addiction. Respiratory side effects can include depression of breathing and cough; extreme caution is warranted if you have asthma or chronic obstructive lung disease. Other side effects could be nausea and vomiting, constipation (never take opioids together with anti-diarrhoeal drugs), constriction of the gall-bladder sphincter (it can make a gallbladder crisis worse), difficulty in passing urine and itching. If you take opioids for a long time, the effects could fade.

Different opioids should not be combined, as this increases the risk for possible side effects without increasing the efficacy of the medication.The codeine levels in combination-type medications that contain codeine are quite low, and may even be too low to relieve pain, but high enough to cause drowsiness.

Reviewed by Prof CL Odendal, senior specialist at the department of anaesthesiology at the University of the Free State, April 2010.

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