The positive treatment effects of clinical trials that were ended early were often exaggerated, according to a study published Tuesday in the Journal of the American Medical Association.

The conclusion was based on an international study by a team lead by Victor Montori, an endocrinologist at the Mayo Clinic in Rochester, Minnesota.

The team studied 91 clinical trials that were ended early, and compared them to 424 trials that were completed.

The trials that were ended early were cut short because of what appeared to be convincing evidence that the experimental treatment was markedly better than the existing therapy.

Test subjects taking a placebo could then also take the drug that was being tested, and the item could be on the market sooner, the researchers said.

Almost everyone - doctors, researchers, funding sources, pharmaceutical firms, scientific journals, even reporters - benefits from a trial ending early, Montori said.

Patients, however, may end up with a treatment that may not be as beneficial as it appears.

"Our research shows that in most cases early stopping of clinical trials resulted in misleading estimates of treatment effects," Montori said.

"These misleading estimates are likely to result in misguided decisions about the trade-off between risks and benefits of a therapy."

Montori and the authors urged researchers to resist pressure to end clinical trials early and continue the tests for longer periods before they consider early termination.