Provision of information about drug side-effects to patients.

To make informed decisions about taking medicinal drugs, people need accurate information about side-effects. A European Union guideline now recommends use of qualitative descriptions for five bands of risk, ranging from very rare (affecting <0.01% of the population), to very common (>10%). We did four studies of more than 750 people, whom we asked to estimate the probability of having a side-effect on the basis of qualitative and quantitative descriptions. Our results showed that qualitative descriptions led to gross overestimation of risk. Until further work is done on how patients taking the drugs interpret these terms, the terms should not be used in drug information leaflets.