Fenfluramine and Phentermine are two active ingredients that were found in a drug under the name Fen-Phen intended to treat overweight.

At the end of the 20th century, production of this drug was prohibited in the United States. This was associated with side effect occurring after using this medication.

There were several other drugs with the same composition as Fen-Phen on the American market. They all were withdrawn from the pharmaceutical market.

A relationship was established between Fen-Phen use and occurrence of problems with heart valves, as well as with an increased risk of developing pulmonary hypertension.

Fenfluramine is an agent that stimulates the release of serotonin, but Phentermine – the production of norepinephrine. Side effects of each of these drugs alone were not reported.

Fenfluramine came into the market in the 1970s, but did not become popular because weight loss was insignificant after its administration. Patients lost up to 8 kg for six months using it.

However, this indicator was significantly higher in combination with Phentermine. Many specialists used this combination to treat obesity.

After the publication of information on the increased risk of cardiovascular side effects, Fen-Phen ceased to be used in medical practice.