Prescription Weight Loss Medicine

Prescription weight loss medications treat obesity.

The Cleveland Clinic

Weight Loss:
Prescription Weight Loss Medicine

Obesity often requires long-term treatment to promote and sustain weight loss. As in other chronic conditions, such as diabetes or high blood pressure, long-term use of prescription medications may be appropriate for some people. While most side effects of prescription medications for obesity are mild, serious complications have been reported (see below.)

Keep in mind that these drugs are not a cure-all. The use of weight-loss medications should be combined with physical activity and improved diet to lose and maintain weight successfully over the long term .

Do I Need Medicine to Lose Weight?

Using prescription drugs to treat obesity should be used as an option for the following individuals:

  • People with a body mass index (BMI) > 30 with no obesity-related conditions.
  • A person with a BMI of > 27 with two or more obesity-related conditions .

What Prescription Medicines Are Used to Treat Obesity?

Currently, most available weight-loss medications approved by the FDA are for short-term use, meaning a few weeks or months. There are many other medications in addition to the most common medications noted below.

Most available weight-loss medications are "appetite-suppressant" medications. These include: Didrex, Tenuate, Sanorex, Mazanor, and Adipex-P. These medications generally come in the form of tablets or extended-release capsules (pills that release medication over a long period of time). Appetite suppressants can be obtained by a doctor's prescription or purchased over the counter .

In the mid 1990s doctors also prescribed the popular appetite suppressant Redux or the combination of phentermine and fenfluramine, called "Phen-fen." However fenfluramine (Pondimin) and Redux were withdrawn from the market in 1997 because they caused damage to heart valves. Phentermine is still available. Taking phentermine alone has not been associated with the adverse health effects of the fenfluramine-phentermine combination. Meridia was withdrawn from the market by the FDA in 2010, as it was found to also damage the heart.

Another type of prescription weight loss drug is a fat absorption inhibitor. Xenical is the only example of this type of treatment approved for use in the U.S. Xenical works by blocking about 30% of dietary fat from being absorbed, and is the most recently approved weight loss drug.

In 2012, the FDA approved two drugs for long-term weight loss, lorcaserin hydrochloride (Belviq) and phentermine/topiramate Xenical and Contrave areis other weight-loss medications approved for longer-term use in significantly obese people, although the safety and effectiveness have not been established for use beyond 1 year.

How Do Appetite Suppressants Work?

Appetite suppressants promote weight loss by tricking the body into believing that it is not hungry or that it is full. They decrease appetite by increasing serotonin or catecholamine -- two brain chemicals that affect mood and appetite.

How Do Fat Absorption Inhibitors Work?

Fat-absorption inhibitors work by preventing your body from breaking down and absorbing fat eaten with your meals. This unabsorbed fat is eliminated in bowel movements.

Do Prescription Weight Loss Drugs Really Work?

In general, Xenical is moderately effective, leading to an average weight loss of 5 to 22 pounds over a 1 year period, more than what would be expected with non-drug treatments. However, the response to these medications is based on each individual, and some people experience more weight loss than others. Likewise, there is no one correct dose for these medications. Your doctor will decide what works best for you based on his or her evaluation of your medical condition and your response to treatment.

Some people have lost more than 10% of their initial body weight with the help of prescription medications. This is a large enough amount to reduce the risk of high blood pressure, diabetes and other obesity-related health complications . Patients generally experience a maximum weight loss within 6 months of starting medication treatment.

Over the short term, weight loss due to prescription drugs may reduce a number of health risks in obese individuals. However, there are currently no studies to determine the effects of these medications over the long term.

Are There Risks to Taking These Medications?

When considering the use of long-term weight-loss medication treatment for obesity, the following possible concerns and risks should be discussed with your doctor:

  • Addiction. Currently, all prescription medications to treat obesity except Xenical are "controlled substances." This means that doctors are required to follow certain restrictions when prescribing them since they could be addictive.
  • Developed tolerance. Most people's weight tends to level off after 6 months while taking a weight-loss medication. This leads to a concern that the person has developed a tolerance for the medication. However, it is unclear whether this leveling off is indeed due to a developed tolerance or if the medication has reached its limit in effectiveness.
  • Side effects. Most side effects of weight loss medications are mild (although some can be unpleasant) and usually improve as your body adjusts to the medication. Rarely, serious and even fatal outcomes have been reported.

What Are the Side Effects?

Most appetite suppressants are used as a short-term treatment for people with obesity. Not only do the drugs' effects tend to wear off after a few weeks, but they can also have some unpleasant side effects, including:

Some side effects with Xenical include, gas with discharge, urgent need to go to the bathroom, oily or fatty stools, an oily discharge and spotting, increased number of bowel movements and the inability to control bowel movements. These side effects are generally mild and temporary, but may be worsened by eating foods that are high in fat. Because Xenical reduces the absorption of some vitamins, people taking Xenical should take a multivitamin at least 2 hours before or after taking the medication.

In the event that any of the following symptoms occur while taking Xenical, you should call your doctor as soon as possible.

  • Achiness
  • Chills
  • Irregular heartbeat
  • Painful menstruation
  • Swelling of the body or of the feet and ankles

Because of the short-term effects of these drugs, it is important for people who are trying to lose weight to learn new eating habits and to exercise while the drug is still effective. Once healthy eating and regular exercise have been learned and established, it is important to continue eating right and exercising if you hope to continue losing weight and keep lost weight from returning.

Appetite suppressants are not for everybody. For example, there are limited studies on these medications' effects on older adults and no studies have been done on children.

What Should I Discuss With My Doctor Before Taking Weight Loss Medicine?

Before a doctor will prescribe a prescription weight loss drug, he or she will ask you about the following: any existing allergies you may have, whether or not you are pregnant or breastfeeding, and what types of other medications you may be taking. Existing medical conditions may also affect the use of these drugs. You should tell your doctor if you have any of the following conditions.

People who are prescribed appetite suppressants should follow the prescription carefully. Because appetite suppressants may cause drowsiness or lightheadedness, it is important to know how you respond to these medications before you attempt to drive or operate machinery.

Are There Other Precautions to Take When Using Anti-obesity Medications?

  • Follow the directions on your prescription label carefully. If there is any part that you do not understand, ask your doctor or pharmacist.
  • Do not take any more or less medicine than prescribed and do not take it more often than prescribed.
  • If you miss a dose, take it as soon as possible. However, if it is close to when you are scheduled to take your next dose, simply skip the missed dose and proceed with your regular schedule. Do not take a double dose.
  • These medications should be kept in their original container, tightly sealed and away from children.
  • They should be stored at room temperature, away from excess heat and moisture (not in the bathroom or near the kitchen sink).
  • Any medication that is outdated or unused should be thrown away.

Taking these medications too often or in too large a quantity, or for longer than prescribed can lead to addiction or, in worst-case situations, an overdose. Symptoms of an overdose can include confusion, convulsions, hallucinations and coma. If you experience any of the following symptoms, call your doctor immediately.

  • A decrease in the ability to exercise
  • Chest pain
  • Swelling in the feet or lower legs
  • Difficulty breathing


  1. MedicineNet


Medically reviewed by Robert Bargar, MD; Board Certification in Public Health & General Preventive Medicine August 2, 2017

Portions of this page from The Cleveland Clinic 2000-2004.

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