It is a relatively safe drug for the relief of mild to moderate pain and fever, but will cause liver damage if overdosed. The recommended dosage limit is four grams of paracetamol over a 24-hour period and a maximum single dose of one gram every four to six hours.

In Hong Kong, there are well over 900 registered pharmaceutical products containing paracetamol in different dosage forms and strengths.

It is a popular ingredient found in many multi-component cold and cough preparations and even in proprietary Chinese medicines, therefore it is important to note the amount of paracetamol in each dose unit so as not to exceed the four-gram daily limit.

The consequence of taking too much paracetamol over a long period of time could be life-threatening.

Normally paracetamol is cleared from the body by conversion into non-toxic metabolites in the liver, but about 10 per cent will be converted into a liver-damaging metabolite, which is detoxified by glutathione which is present in the liver.

People who take too much paracetamol produce excessive amounts of this toxic compound that depletes the store of glutathione, resulting in liver damage and, if not treated promptly, can lead to liver failure and death.

For pain with swelling and inflammation, non-steroidal anti-inflammatory drugs (Nsaids) with better anti-inflammatory activities can be used. However, prolonged usage of Nsaids could lead to a higher risk of heart attack and stroke, as well as hypertension and kidney problems.

There are some important points to be observed in using painkillers.

Aspirin is a salicylate with action similar to Nsaids, but it is not suitable for children below the age of 16 as it can induce Reye's syndrome with damaging effects to multiple organs, including the brain and liver. People with asthma and breathing problems should avoid using aspirin and Nsaids.

Pregnant women should not use any drug, particularly during the first 12 weeks of pregnancy unless under medical supervision. If painkillers have to be used during this period, paracetamol is a good choice, while Nsaids like Ibuprofen should not be used in the last trimester of pregnancy. This is because they can cause a dangerous rise in blood pressure inside the lungs of the baby.

Frequent use of painkillers can result in a medication over-use headache that cannot be relieved or can even worsen with the use of painkillers. The only way to deal with this is to stop using the drug immediately or seek medical advice. Long-term use of high doses of paracetamol carries the same risk as Nsaids, such as hypertension, myocardial infarction, stroke, bronchoconstriction and renal failure.

Headaches with the following characteristics, however, require immediate medical attention and should not be self-treated. Worsening headache with fever, frequent severe headache, thunderclap headache of sudden-onset reaching maximum intensity within five minutes, headache triggered by coughing, sneezing, laughing, straining, exercise, body position and jaw claudication, new-onset neurological and cognitive dysfunctions, recent head trauma, neck stiffness, nausea, visual disturbance, painful red eye, misty vision or haloes and semi-diluted pupils.