Nobody knows the answer.
On the other hand, researchers say that if the weight-loss drugs are to blame, a likely link is their highly potent effect on serotonin, a brain chemical that regulates moods and emotions. Even as scientists race to untangle the serotonin-heart valve link, new evidence emerging this week suggests the research that led to last week's recall may be flawed. My group was a biased sample. The FDA confirmed that Dr. Bowen contributed a large number of patients, but declined to say how many. While many scientists feel there is strong evidence that the diet drugs do cause some damage, it's unclear how extensive the damage is, or whether it's reversible once the drugs are stopped.