Appetite Suppressants (Sympathomimetics) for Obesity

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Appetite Suppressants (Sympathomimetics) for Obesity


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How It Works

Sympathomimetic appetite suppressants make you feel less hungry. They work by changing levels of brain chemicals (neurotransmitters) that affect mood and appetite. This medicine tends to work for only a few weeks, so it is not recommended for long–term use. That is why it is important to learn healthy habits for eating and getting more active.

Why It Is Used

Appetite suppressant medicines help people who are obese (those with a body mass index [BMI] of 30 or higher) to lose weight. It may also be prescribed for people who have BMIs of 27 or higher when they have other health conditions (such as diabetes, high blood pressure, or high cholesterol) that are made worse by being overweight.

How Well It Works

These medicines work to decrease your appetite for only a few weeks. They are not meant for long-term use. If you think they are not working, do not take more than the dosage prescribed. Talk to your doctor. Taking too much of this medicine can cause side effects and may lead to a habit.

A review of research reports that using phentermine may result in more weight loss than when taking a placebo. Most of the people using phentermine also made lifestyle changes, such as diet or exercise.1

Side Effects

All medicines have side effects. But many people don't feel the side effects, or they are able to deal with them. Ask your pharmacist about the side effects of each medicine you take. Side effects are also listed in the information that comes with your medicine.

Here are some important things to think about:

  • Usually the benefits of the medicine are more important than any minor side effects.
  • Side effects may go away after you take the medicine for a while.
  • If side effects still bother you and you wonder if you should keep taking the medicine, call your doctor. He or she may be able to lower your dose or change your medicine. Do not suddenly quit taking your medicine unless your doctor tells you to.

Call 911 or other emergency services right away if you have:

  • Trouble breathing.
  • Swelling of your face, lips, tongue, or throat.
  • Chest pain.

Call your doctor if you have:

  • Hives.
  • Diabetes and you notice a change in your blood sugar.
  • Noticed that you have a harder time exercising after you started taking the medicine.
  • Become addicted to the medicine.

Common side effects of this medicine include:

  • An increase in blood pressure.
  • Headache.
  • Nervousness or restlessness.
  • Constipation.
  • Dry mouth.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Phentermine is no longer marketed in Europe due to a possible association with heart and lung problems.1

To help prevent sleeplessness, take these types of medicines at least 4 to 6 hours before you go to bed.

Taking medicine

Medicine is one of the many tools your doctor has to treat a health problem. Taking medicine as your doctor suggests will improve your health and may prevent future problems. If you don't take your medicines properly, you may be putting your health (and perhaps your life) at risk.

There are many reasons why people have trouble taking their medicine. But in most cases, there is something you can do. For suggestions on how to work around common problems, see the topic Taking Medicines as Prescribed.

Advice for women

Women who use this medicine during pregnancy have a slightly higher chance of having a baby with birth defects. If you are pregnant or planning to get pregnant, you and your doctor must weigh the risks of using this medicine against the risks of not treating your condition.


Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.



  1. Arterburn DE, et al. (2008). Obesity in adults, search date February 2007. Online version of BMJ Clinical Evidence:


ByHealthwise Staff
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerTheresa O'Young, PharmD - Clinical Pharmacy
Last RevisedMay 14, 2012

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