Patients May Overestimate Unwanted Effect Risks

Patients May Overestimate Side Effect Risks From Drug Labels

LONDON (Reuters Health) Mar 08

British researchers have called for European Union (EU) guidelines to be revised after finding that patients greatly overestimate the risk of drug side effects when given only qualitative information about risks.

Professor Dianne C. Berry, from the University of Reading, and colleagues, at University of Leeds, explain that EU guidelines, which came into force in January 1999, recommend that drug information categorises the risks of side effects into five bands. These range from very rare, affecting fewer than 0.01% of the population, to very common, affecting more than 10%.

The research team carried out four studies in which more than 750 adults recruited from public places were asked to estimate the probability of experiencing side effects when given qualitative or quantitative information on prescribed drugs. Their findings are reported in the March 9th issue of The Lancet.

In the largest of these studies, 360 adults were given qualitative descriptions of "common" and "rare" for the occurrence of side effects, which corresponded to actual risks of 2% and 0.02%, respectively.

The study team found that participants vastly overestimated the risk of side effects. People in the study thought that the personal risk associated with the word common was 50%, and the corresponding figure when given the word rare was 21%.

"To make informed decisions about taking medicines people need accurate information on side effects. While attempting to be helpful, the EU really put the cart before the horse because they issued the guidelines before there was any evidence that the words associated with risk would be meaningful," said study co-author Professor D. K. Raynor.

"Not only did participants given qualitative information believe the probability of side effects to be significantly higher than the true risk, but our study suggested that they were nearly two times less likely to comply with treatment," he added.

When patients were given quantitative information on risk they still perceived the level of risk to be greater than the actual risk. Those given a numerical value of 2% perceived their actual risk to be 9.5%; when given a value of 0.02%, they estimated their risk of side-effects to be 7.0%.

"One possible reason is that people have a healthy scepticism on the health information they are provided with. They may feel that the numbers given are an underestimate," Prof. Raynor suggested.

The researchers say that terms like rare or common should not be used until research shows how people interpret them.

"We need to come up with something that does work, and my view is that we still need to use verbal descriptions," Prof. Raynor continued. "For example, if the real risk of side-effects is 10%, we need to find the word that is perceived by patients to match that figure most closely. An average drug has a list of 20 to 30 potential side effects so depicting the risk levels quantitatively for each drug will be confusing. More research is needed to assess which words are perceived to correspond most closely with the actual figures for risk."

Prof. Raynor and his colleagues are currently studying other aspects of drug labelling. "If someone feels they have a side effect listed on the medication, they need to know what they should do," Prof. Raynor said. "Currently, the guidelines suggest that action should be taken 'immediately' or 'as soon as possible'. Our preliminary data suggest that patients do not distinguish between these options, so the distinction is effectively meaningless."

Prof. Raynor and colleagues are currently working in partnership with academics in other EU states to see if their findings are applicable across the region.

Noel Wathion, from the European Medicines Evaluation Authority, appeared to query the rationale behind the study.

Although he said he had not had the opportunity to look at the paper in depth, he pointed out that the EU guidelines favoured the use of numerical rather than qualitative information. "We plan to review the outcome of this study in more detail and in the context of the EU guidelines," he said in an interview.

Lancet 2002;359:853-854.

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