An international study of nearly 100 clinical trials that were stopped early after positive results has found that many of the therapeutic effects were exaggerated. In the Journal of the American Medical Association, the authors recommend that drug researchers resist pressures to end clinical trials early and instead continue them longer before even considering premature termination.

“In most cases, early stopping of clinical trials resulted in misleading estimates of treatment effects … likely to result in misguided decisions about the trade-off between risks and benefits of a therapy,” said corresponding author Victor Montori of the Mayo Clinic. “On average, treatments with no effect would show a reduction in relative risk of almost 30% in stopped early trials. Treatments with a true relative risk reduction of 20% would show a reduction of over 40%.”

Clinical trials end early because of a convincing (usually large) apparent difference between an experimental treatment and an existing standard therapy Studies end so participants taking a placebo or less effective medication can also take the studied drug if it seems to work well. Doctors can prescribe a therapy sooner if it reaches the market earlier. Montori says almost everyone benefits from a trial ending early — doctors, researchers, funding sources, pharmaceutical companies, scientific journals, even reporters — everyone except patients, who may ultimately take the wrong drugs.

The study authors recommend that researchers use restraint and truncate clinical trials only near their end — and only with very good reason. Otherwise, says Dr Montori, patients and physicians could be making treatment choices based on inaccurate information, or worse, choosing one treatment when another may be more appropriate.