Phentermine is a regulated prescription medication used to reduce appetite.
Phentermine is a prescription weight loss drug. The FDA approved it in 1959 for short-term use in people over 16.
In the 1990s, it was part of a combo called fen-phen. The FDA later pulled the other drugs due to heart risks.
Today, phentermine is sold under different brand names. You can take it alone or with other medications.
Because it can be habit-forming, doctors prescribe it only for short periods. It’s meant for people with obesity or weight-related health problems.
Phentermine is an appetite suppressant. It helps reduce calorie intake by making you feel less hungry, which may lead to weight loss.
Doctors believe phentermine works by increasing certain brain chemicals—norepinephrine, serotonin, and dopamine. These chemicals send signals that reduce hunger.
However, your body can build tolerance to phentermine after a few weeks. If that happens, talk to your doctor about next steps.
Studies show phentermine helps with weight loss, even though it’s only FDA-approved for short-term use (up to 12 weeks).
However, doctors sometimes prescribe it for longer, often recommending short breaks in between. Most people lose about 3–7% of their starting weight within 3 to 6 months.
When combined with topiramate (sold as Qsymia), phentermine leads to even more weight loss than when used alone. This combo helps more people lose at least 5% of their body weight compared to other weight-loss medications.
Average weight loss with different Qsymia doses:
•3.75/23 mg: 7.8 pounds (3.55 kg)
•7.5/46 mg: 16 pounds (7.27 kg)
•15/92 mg: 18 pounds (8.25 kg)
This weight loss often comes with a smaller waistline, better blood sugar control, improved insulin sensitivity, and lower blood pressure.
With a prescription, the price of a month’s supply of phentermine can vary significantly, ranging from $30 to upwards of $200, contingent upon the brand, formulation, and strength of the medication.
