Phentermine is well known as an appetite suppressant. Today it is the most commonly prescribed of all FDA approved diet drugs. While new patients are using Phentermine each day, very few people realize what a long and interesting history this drug actually has.

Phentermine first received FDA approval in 1959. This first form of Phentermine was Phentermine resin. Phentermine resin was prescribed by some physicians as an appetite suppressant, but the drug did not begin to experience true popularity with the public until the 1970s.

Phentermine Hydrochloride is the form of the drug which was introduced in the early years of the 1970s, and while this was simply a slight evolution of Phentermine resin, it grew to be very well known among diet patients. At this time the drug was most often sold as Fastin, Lonimin, Adipex-P, or the generic version known simply as Phentermine. The earliest users of the medication were told to take the medication without any other medications. Soon, that was to change with the phenomenon Phentermine “cocktails”.

In 1973, a drug called Fenfluramine was approved by the FDA for the short-term treatment of obesity. When Fenfluramine was reported by many patients to be inefficient in appetite supression, some doctors began prescribing what would become known as the “Phen-Fen cocktail”. While the FDA did not specifically approve the use of Fenfluramine and Phentermine together, doctors were free to combine them using a practice known as “off label” prescribing because they were both FDA approved drugs. When Fenfluramine and Phentermine were combined, they resulted in a very strong combination diet drug which soon became extremely popular. With millions of prescriptions written every year, and diet clinics opening which focused solely on Phen-Fen, the drug reached peak popularity in the 1990s, and that popularity continues even today.

Phen-Fen maintained its position as top diet drug for many years, for a time in the mid 1990s sharing popularity with another diet drug cocktail. “Dexfen-Phen” was a combination of Dexfenfluramine and Phentermine, using the newly FDA approved weight loss drug Dexfenfluramine. This new Phentermine based drug cocktail was very similar to Phen-Fen, with near identical effects.

The Phentermine combination cocktails were some of the most prescribed drugs of any kind until 1997, when the Mayo clinic released findings regarding Dexfenfluramine and Fenfluramine. Certain problems with heart valves were found in patients who had taken these two drugs, luckily Phentermine was not in any way related to these reactions. Following the FDA’s release of the Mayo clinic findings, further studies were undertaken.

Based on these findings of these studies, which were focused exclusively on Dexfenfluramine and Fenfluramine, the FDA requested the withdrawal of the two drugs found to cause the problems. Dexfenfluramine and Fenfluramine were promptly withdrawn from the market. Since Phentermine had proven to be merely part of the drug mix, but was clearly not the drug causing the heart damage, the FDA did not request its withdrawal from the market. Phentermine was never, at any time, found to be the cause of any medical problems and in fact, has been proven to be consistently effective for 50 years now.

In more recent times, another Phentermine cocktail has emerged. With “Phen-Pro”, Phentermine is combined with Prozac or another antidepressant. While Prozac is normally used as a mood elevator, it is prescribed in this cocktail due to its ability to help Phentermine be more effective over longer periods of time. Normally, Phentermine loses some of its ability to promote weight loss after a short initial period of use. With Phen-Pro, it appears that the appetite suppressant effects can be extended for even longer. Just as with the previous cocktails, the FDA has not approved the use of these drugs in combination, and Prozac and Phentermine are prescribed together off label only.

Phentermine has had a very long and interesting history, but it remains the single most effective and successful diet drug ever. In its 50 years on the market, Phentermine has proven to be effective when used alone, and in combination with other medications as well.