Fenfluramine, part of the fen/phen obesity drug that was banned in the U.S. in 1997 after it was linked to heart problems, is still causing damage, according to a new report.

People who stopped using the drug had damaged heart valves up to seven years later, researcher Charles Dahl from the Central Utah Clinic said.

Dahl studied the hearts of 5,743 former fenfluramine users.

"Valve problems were common in individuals exposed to fenfluramines, more frequent in females and associated with duration of drug use in all valves assessed," he said in a news release. The valves ensure blood flows in the correct direction through the heart.

A news release on the study said that the risk of heart-valve surgery was seven times higher for people who took fen/phen, though less than one-half of a percent of users had required surgery.

Since its withdrawal, there have been reports that tens of thousands of lawsuits have been filed against the drug's manufacturers.