Many US adults believe that the US Food and Drug Administration (FDA) only approves drugs that are extremely effective and have no serious side effects, a new study has found.

The research, reported in the Archives of Internal Medicine September issue, found that 39% of participating adults believed that the FDA only approves prescription drugs that are "extremely effective," while 25% thought the agency only approves products which do not have serious side effects. Moreover, 25% believed that only extremely effective drugs can be advertised, and 17% thought that medicines which have serious side effects cannot be advertised.

In fact, FDA approval does not necessarily ensure that a drug has a large or important benefit, or that all serious adverse effects are known, according to authors Lisa Schwartz and Steven Woloshin. "Uncertainties are greatest in the first few years after approval and for drugs approved solely on the basis of a surrogate outcome," they add.

Moreover, they point out that the FDA has never required advertisements to acknowledge uncertainties inherent in all new drugs.

The "important gaps" in what people know about prescription drugs revealed by their research "undoubtedly contribute to the rapid uptake of drugs despite uncertainty about benefit and harm," say Drs Schwartz and Woloshin, but they also report the results of a randomised controlled trial which show that giving patients explanations highlighting uncertainties about drug benefits can help them improve their choice of treatment. 

"Simple explanations (ones that are brief enough even for television advertisements) can help consumers make better decisions," they say, and comment that the "enthusiasm" for Merck & Co's cholesterol-lowerer Zetia (ezetimibe) and withdrawn anti-inflammatory Vioxx (rofecoxib) "might have been dampened had consumers known to look for drugs approved based on patient outcomes or drugs with a longer safety record."  

The authors also call on the FDA to communicate more effectively what it knows and does not know about how well drugs work.