We all experience pain at one time or another during our lives so it's helpful to understand how painkillers actually work!
Painkillers fall into two categories, namely non-opioids and opioids and there are two ways in which painkillers work.
Either they block the nerve pathways that transmit pain signals from the body to the brain or by reducing the perception of pain by preventing further transmission of pain signals once they reach the brain!
Non-opioid painkillers are not as strong as opioids and many are available over-the-counter. Their side effects are rarely a problem if they are taken occasionally, as suggested and according to the recommended dosage.
Two types of non-opioid drugs are available and include:
Nonsteroidal Anti-inflammatory Drugs (NSAIDs)
Nonsteroidal anti-inflammatory drugs or NSAIDs, such as Fastum, are used to treat mild to moderate pain. In addition to relieving pain, they also reduce inflammation or swelling that often accompanies pain and makes it worse.
NSAIDs work at the site of pain to prevent the stimulation of nerve endings and provide relief by reducing the sensation of pain and reducing inflammation that often accompanies pain and worsens it.
The efficacy of NSAIDs is based upon the fact that they reduce the production of chemicals called prostaglandins that are responsible for swelling and pain found in inflamed tissue.
NSAIDs are most commonly used to treat muscle and joint pain but may also be used to treat other types of pain such as period pain.
Since NSAIDs irritate the stomach lining and can cause digestive upsets such as heartburn, indigestion, nausea, bloating, diarrhoea and stomach pain and even ulceration and bleeding, it is recommended that they be taken immediately after eating a meal.
NSAIDs should be taken at the lowest effective dose for the shortest duration.
Paracetamol
Paracetamol, such as Panado®, is the most widely used painkiller and, if taken as prescribed, can be one of the safest analgesics. It can be used for everyday pain such as headaches, toothache and joint pain. Not only is it used to treat adult pain and fever, but also that experienced in babies and children.
Like the opioids, paracetamol works on the brain and spinal cord to reduce the perception of pain. It is thought that paracetamol works by reducing the production of chemicals called prostaglandins in the brain. Since it only affects the production of prostaglandins in the brain and not the rest of the body, it has no effect on inflammation or swelling. It can, however, lower temperature.
Unlike NSAIDs, paracetamol does not usually irritate the stomach lining and in this way cause gastrointestinal discomfort or upset. However, a paracetamol overdose can cause severe liver or kidney damage.
Opioids are powerful painkillers which have similar properties to drugs that are derived from opium such as morphine. Opioids are given to treat pain that occurs during a heart attack or a myocardial infarction, pain following surgery or a serious injury and even pain experienced with cancer.
Dependence may occur if opioid painkillers are taken for an extended or long period of time. This is because prolonged usage leads to tolerance which means that higher doses of the painkiller need to be given to achieve the same effect or level of pain relief. A person is unlikely to become dependent if they take the painkiller for a few days only to relieve severe pain.
Side effects that may be experienced with opioids include clouded thought, nausea, vomiting, constipation, drowsiness and depressed breathing.
Opioids work directly on the brain. They work in the same way as endorphins which are substances that are naturally produced by the brain in response to pain. Endorphins stop the cell-to-cell transmission of the pain signal in the brain.
Opioid medicines include:
Codeine
Codeine is considered to be a mild opioid analgesic that is mostly used to relieve mild to moderate pain. Although it is similar to morphine, it is weaker. Many drug formulations combine codeine with a non-opioid analgesic such as paracetamol. Codeine is habit-forming. However it is seldom that addiction will occur if it is taken for a short period of time at the recommended dosage. A common side effect that may occur with codeine usage is constipation.
Mephenesin
Mephenesin works on the brain to provide a muscle relaxant effect for pain that is associated with tension.
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The British Medical Association New Guide to Medicines and Drugs 7th Edition 2007:80-1,252,395
Martindale The Complete Drug Reference 33rd Edition 2002:27-8,69,1329