Phentermine and Topiramate

How Does It Work?

As mentioned, this drug contains two medications, phentermine and topiramate. Phentermine is a weight-loss medicine that is chemically related to amphetamines. It is thought to primarily work by increasing the release of certain naturally occurring substances in the hypothalamus, a part of the brain that helps control appetite. This action helps to suppress appetite, decreasing the amount of food a person eats.
It is not entirely clear how topiramate, the other active ingredient in the diet pill, helps with weight loss. It is thought that the medication primarily works in the brain to suppress appetite and enhance feelings of fullness.

Clinical Effects of Phentermine and Topiramate

In clinical studies, phentermine and topiramate helped people who were overweight and obese lose weight. In these studies, up to 70 percent of people taking phentermine and topiramate for a year lost at least 5 percent of their body weight, and up to 48 percent of people lost at least 10 percent of their weight.
In comparison, 21 percent of those taking a placebo (a "sugar pill" with no active ingredients) had lost at least 5 percent of their weight after a year, while only 7 percent had lost at least 10 percent of their previous weight.
It should be noted that everyone in the study also consumed a low-calorie diet and increased their physical activity.

When and How to Take This Medicine

Some general considerations to keep in mind during treatment with phentermine and topiramate include the following:
  • Phentermine and topiramate comes in the form of a capsule. It is usually taken by mouth once a day.
  • You can take phentermine and topiramate with or without food. Try taking it with food if it upsets your stomach.
  • You should take your dose in the morning, as taking it later in the day could cause insomnia.
  • Take this medication at the same time each day to keep an even level of the drug in your bloodstream.
  • Do not stop taking phentermine and topiramate suddenly, as doing so could cause serious problems, such as seizures. If you no longer need it, your healthcare provider may want to gradually reduce your dose.
  • Phentermine and topiramate is used in combination with a reduced-calorie diet and exercise program. Make sure to follow your complete weight-loss program for the best results.
  • For the medication to work properly, it must be taken as prescribed. Taking more than the recommended amount could increase your risk for serious side effects.
Last reviewed by: Kristi Monson, PharmD
9 Signs You May Have Hyperactive-Impulsive Type Adult ADHD