The treatment effects of drugs are conventionally estimated in randomised controlled trials. Random allocation of patients ensures that any difference in outcome observed between the experimental groups must be attributable either to chance or to the randomised treatments. Although a remarkably durable approach, randomisation does have limitations. Randomised trials conducted for regulatory purposes rarely include people with comorbidities, since adverse events observed as a result of these comorbidities may undermine the attempts to establish the safety of the new drug. Furthermore, randomised trials are costly and time consuming and may not be conducted by industry sponsors when a “positive” outcome seems unlikely. Thus health policy makers often have to make important decisions about new drugs when not all relevant trials have been undertaken. This is the situation currently regarding the use of antiviral therapy in H1N1 influenza. It may be argued that at such times we should be informed by all available evidence and not constrained by randomised trials alone.

The authors of the Cochrane Collaboration systematic review of neuraminidase inhibitors for preventing and treating influenza in healthy adults1 approached Roche, the manufacturer of oseltamivir, for unpublished data. Among the incomplete data that Roche provided was a list of observational studies that it considered to describe the “real life” value of antiviral treatment. The BMJ invited us to provide a rapid review of these studies and the extent to which they support the use of oseltamivir to treat influenza in healthy adults.