Benfluorex, commonly known as Mediator, a diabetes drug that was widely prescribed as a slimming aid, has been responsible for thousands of hospitalizations and deaths in France before it was withdrawn.
Mahmoud Zureik of the National Institute of Health and Medical Research (Inserm), who co-led the probe, told AFP that around 3,100 people had required hospitalisation during the 33 years during which the drug was sold.
However, these figures could well be an "underestimate," he said.
Mediator, known by its lab name as benfluorex, was initially licensed to reduce levels of fatty proteins called lipids, with the claim that it helped diabetics control their level of blood sugar.
But it also suppressed appetite, which meant it gained a secondary official use to help obese diabetics lose weight.
In fact, it was widely sold on prescription for non-diabetics wanting to slim.
In 2009, Mediator was pulled from the European market amid evidence that it damaged heart valves and caused pulmonary hypertension.
Its French manufacturer, Servier, is being probed on suspicion of dishonest practices and deception.
The new study is an extrapolation based on figures for deaths from faulty heart valves, although not from hypertension, among major users of the drug.
The main data comes from France's national health insurance system, which said that 303,000 patients used Mediator in 2006.
According to Mediator, 145 million packets of Mediator were sold on the French market before the drug was pulled.
The Mediator case came to light after a scandal involving a similar type of anti-obesity drug, fenfluramine, in the late 1990s.