"If you kick out the 940 worst patients in terms of adverse drug responses, then still have worse outcomes on the drug, imagine how bad it would have been if you included the dropouts. This is fake research, and sadly typical for company-sponsored studies," said Dr. John Pippin, senior medical and research adviser for the Physicians Committee for Responsible Medicine.
Conversely, the fact that all subjects were already at increased cardiovascular risk by virtue of the fact that the study selected for this trait, some might argue that the increased risk could be avoided if doctors prescribed the diet drug only to patients who are in good cardiovascular health.
"Those receiving treatment in the study are a homogenous population," Niswender said. "But as physicians we tailor therapies to patients."
Though only a minority of obese patients does not suffer from increased cardiovascular risk, Niswender said it is possible these patients could benefit from the drug without seeing undo increase in risk.
However, some preliminary data show an increase in adverse cardiac events, even in those in good cardiovascular health, Pippin said.
Given the small effect on weight seen in trials, he said approving a drug with so little therapeutic effect but a persistent cardiac effect is "crazy."
Meridia's potential to increase heart rate and blood pressure was known at the time of its FDA approval for weight loss back in 1997.
Since then, the company has added warnings concerning the drug, noting that those ever suffering from heart attack, heart arrhythmia, stroke, arterial disease, or uncontrolled high blood pressure should not be on the drug.
Meridia's effect on weight loss and its effect on heart health are indelibly tied, Pippin said.
"When we eat, our brain releases neurochemicals that tell us we're full, the most prominent of which is serotonin. Meridia and certain other diet drugs, they block the action that makes that serotonin go away, giving you the feeling that you are full continually, which makes you eat less," he said.
Unfortunately, the excess presence of these chemicals has potentially negative effects on the cardiovascular system as well, he said, which is why a number of diet drugs that work in this way have ended up causing heart problems in some patients.
A prominent example of this is fen-phen, a popular diet drug of the 1990s. Fenfluramine, a main ingredient in the pill, was found to be associated with valvular heart disease and pulled from the market in 1997.
More recently, Arena Pharmaceuticals has been developing a diet drug thought to use the same pathway as fen-phen but in supposedly safer way. The FDA released a statement Tuesday however, which called out the safety of the new drug, noting issues with heart valve disease and psychiatric side effects with its main ingredient, lorcaserin.
"I think the FDA has been burned with cardiovascular disease for a number of diet drugs that have been on the market," Niswender said. "I think this is part of their rationale for requiring more stringent cardiovascular data up front for diabetes drugs. It's going to take more [in the future] to get these drugs approved."
ABC News' Kim Carollo contributed on this report.