Fen-Phen (in combination), as well as fenfluramine (Pondimin) and a related compound, dexfenfluramine (Redux), used alone, have been associated with serious medical complications.

These complications include: valvular heart disease (damaged heart valves), PPH (Primary Pulmonary Hypertension) and neuropsychological complications (memory impairment, behavioral changes, depression or mood swings and psychosis).

The FDA (Food and Drug Administration) approved the use of both components of Fen-Phen (fenfluramine and phentermine) and the related drug dexfenfluramine (Redux) based upon manufacturers' research that demonstrated efficacy and safety.

However, the FDA did not approve the combined or prolonged use of these drugs.

While the FDA approves the initial marketing of a drug and specifies indications (diseases or symptoms for which the drug can be used) it does not regulate prescribing practices. Therefore, drugs may be used by individual physicians at their discretion for symptoms or disorders other than those cited by the FDA (off-label use).

Off-label use is a common and necessary part of medical practice. Waiting for FDA approval for every indication would unnecessarily delay and restrict physicians' efforts to treat their patients. In many cases approval will never come, as it depends upon complex, protracted and expensive efforts on the part of pharmaceutical companies to demonstrate that a drug is both effective and safe for each indication.

If physicians have already discovered that a drug is useful in an off-label application, they will prescribe it in that fashion, regardless of a lack of FDA approval.

Unless they believe that FDA approval will lead to an increase in the prescribing practices of physicians (and higher profits that will at least offset the costs of gaining approval) there is no incentive for drug companies to pursue approval for additional indications.

Specifically with respect to fen-phen, physicians used the drugs individually or in combination based upon available evidence that this was safe. No available information suggested that prolonged used was problematic.

As conflicting information became available, physicians altered prescribing practices and exercised greater caution and discrimination.

The FDA intervened and requested that both drugs, fenfluramine (Pondimin) and dexfenfluramine (Fastin), be removed from the market when sufficient evidence accumulated to demonstrate the serious risks associated with these products.

The other component of fen-phen, phentermine (Fastin), was not withdrawn from the market, since it was not shown to be associated with the serious medical conditions that patients were developing.

It has been subsequently shown that American Home Products and Wyeth had knowledge of a higher incidence of serious complications associated with their products (the fenfluramine component of fen-phen and dexfenfluramine), but withheld or minimized this data, and continued to aggressively market these agents despite information that should have resulted in alternative action.