Unclear medicine leaflets lead patients to overestimate the risk of side effects by up to 50 per cent and can influence their decision about whether to take prescribed medication.
The study was published in the British Journal of Health Psychology. Researchers questioned 285 visitors to Cancer Research UK's patient information website, CancerHelp.org.uk.
They found that people interpreted the risk of having side effects differently, when percentages were used as in: '20 per cent of patients will have side effects' or when words were used such as 'common', 'very common' or 'uncommon'.
But they were much more likely to have an accurate understanding of the risks when they were described as ‘one in five people may have side effects'.
Previous studies have shown that patients want straightforward information about their treatment. They are most likely to read leaflets about their medicine when it is first prescribed to them. The risk of side effects will have a big influence on whether they take their medication.
Each patient will react differently to medication and until now it has been unclear how best to explain the risks.
Dr Peter Knapp, study author based at the University of Leeds, said: ‘These are important findings which will help health workers and pharmaceutical companies explain information to patients in the best possible way.'