Wegovy, the promising obesity drug from Novo Nordisk, reduced the risk of serious heart problems by 20% in a large clinical trial. The study results sent weight-loss related stocks soaring and could increase pressure on insurers to cover these treatments.

Insurers, however, tapped the brakes on the optimism. Although the trial results demonstrate that obesity drugs may have significant health benefits beyond shedding unwanted pounds, organizations representing U.S. insurers emphasized that the data are still preliminary. They also expressed concern about the high costs involved with covering those medications, which are nearly $1,350 per month for a single patient.

"It's impossible to evaluate the efficacy and long-term effectiveness of a prescription drug based solely on a drug manufacturer's press release," said David Allen, a spokesperson for America's Health Insurance Plans. "Health insurance providers will continue to analyze new evidence as it becomes available."