We need to get better evidence about harms

Should kids be plastered with sunscreen this summer? Is this likely to be more beneficial than harmful? How would we know? For example, sunscreen use has been associated with overexposure to the sun, perhaps because of overconfidence in its abilities.1 2 Might there also be a potential risk of developing contact allergies, skin irritation, and rare but severe adverse effects? People making a decision about whether or not to use sunscreen need reliable evidence on the balance of benefits and harms. The same is true of all healthcare interventions, and unfortunately reliable evidence on harms is often lacking.

Great progress has been made in obtaining reliable evidence on the beneficial effects of interventions, but developments in the identification, interpretation, and reporting of harmful effects is more challenging. Randomised controlled trials are the best way to evaluate small to moderate effects of healthcare interventions, and much of the evidence for benefits from treatment comes from such studies. However, they are not always suitable to evaluate harms, and this was made clear during a recent meeting jointly organised by the Cochrane Collaboration and BMJ Knowledge in London.

There are various problems with randomised controlled trials in relation to harms and some of these problems affect systematic reviews too. Firstly, trialists may know which benefits to assess …