Diet Drugs


Prescription weight-loss medications are used to help obese people lose weight when the drugs are used along with a program of a healthy diet and exercise.


All prescription weight-loss drugs are intended to reduce caloric intake or increase calorie usage, however the methods vary.


The Food and Drug Administration (FDA) had approved five prescription weight-loss medications for long-term use as of the beginning of 2018. Three of these worked as appetite suppressants by affecting one or more neurotransmitters in the brain. One medication reduced the amount of fat that could be absorbed by the body and another normalized blood sugar to increase satiety. Newer drug development programs have been investigating the molecular mechanisms that underlie the regulation of both appetite and metabolism (energy homeostasis).

Diet pills approved by the U.S. Food and Drug Administration

Generic name

Trade name(s)

Drug type

FDA approval date

Approved for short-term use

benzphetamine hydrochloride


appetite suppressant



Tenuate, Tenuate Dospan

appetite suppressant



Bontril, Plegine, Prelu-2, X-Trozine, Adipost, Melfiat

appetite suppressant



Adipex-P, Fastin, Ionamin, Oby-trim, Pro-Fast, Zantryl

appetite suppressant


Approved for long-term use



appetite suppressant



Xenical, Alli

lipase inhibitor


phentermine and topiramate extended-release


appetite suppressant




appetite suppresssant




appetite suppresssant


Note: The drug sibutramine (Meridia) was previously included in this list but was removed from US markets in 2010 at the request of the FDA.

SOURCE: U.S. Food and Drug Administration.

Weight-loss medications are meant for people who have been advised to lose weight for health reasons, for example, those who have health problems related to obesity, including high blood pressure or type 2 diabetes. Before prescribing a medication, doctors consider current health issues, other medications taken, family medical history, and body mass index (BMI). Those with a BMI of 30 or more or a BMI of at least 27 accompanied by weight-related health problems may qualify. When combined with physical activity and healthy eating habits, people taking these medications lose between 3% and 9% more of their starting body weight than people in a lifestyle program who do not take medication. Most weight loss occurs during the first six months of medication use.

Appetite suppressants (anorexiants)

These medications use neurotransmitters in the brain that control appetite and mood. The model for these drugs is amphetamine. The mechanism of amphetamines on appetite suppression is not fully understood. It is known that amphetamines and amphetamine-like drugs cause the release of norepinephrine and dopamine. Although they are stimulants, amphetamines do not increase the basal metabolic rate, the rate at which the body uses energy while in a resting state. The following medications work by suppressing appetite:

Lipase inhibitors

Orlistat was the first of a class of anti-obesity drugs called lipase inhibitors. Orlistat, marketed under the brand name Xenical, inhibits the pancreatic enzyme lipase that breaks down dietary fat. This decreases the body's absorption of dietary fat by as much as 30%. The undigested fat is excreted in the stool. The FDA approved orlistat for nonprescription sale in 2007.

Blood sugar normalizers

Liraglutide (Saxenda) is similar to a natural hormone in the body (incretin) that helps normalize blood sugar and may increase satiety to control appetite.

Other agents

A large number of other agents have been offered for over-the-counter sale as weight loss agents; however, they have not been either adequately studied or properly standardized and so cannot be recommended. In addition, many of the products marketed as herbal have been found to be adulterated with active drugs, including sibutramine and amphetamine. People taking these agents under the impression that they are safe because they are labeled as natural products may be taking inappropriate doses of active drugs.

Some products claim to increase the body's thermogenesis. These claims purport that the body will burn more calories in the resting state, leading to increased weight loss. Some herbal remedies are based on seaweed, which has a high iodine content. As iodine is needed for the normal function of the thyroid gland, it is claimed that these products may help speed up metabolism. No research has shown that providing more iodine will have this effect. At one time, thyroid hormone was prescribed for this purpose, but because of the very high risks associated with thyroid hormone, this use has been discontinued. Comparable claims have been made for green tea extract, but the weight loss benefits of these products are not clear. In one study, patients taking green tea had greater weight loss than the subjects in the control group, but on careful review, it was found that patients in the active group were exercising more than patients taking placebo. A review of research indicated evidence of a small amount of weight loss using green tea, but it is unlikely to be clinically significant.

A drug that causes loss of appetite. Caloric—Relating to heat or calories.
A neurotransmitter and precursor of norepinephrine; found in high concentrations in the brain.
Nutrients in the diet that are not digested by enzymes. Insoluble fiber travels through the digestive tract and has a laxative effect.
Relating to homeopathy, a system of treating diseases by giving people very small doses of natural substances which, in healthy people, cause the same symptoms as the disease being treated.
A hormone that constricts blood vessels.
Producing heat. Relating to diet drugs, the term indicates a drug which causes increased use of calories without exercise.

Homeopathic remedies have been offered as weight loss products. Homeopathy itself is controversial at best, and no reputable studies indicate that homeopathic remedies have any value in weight reduction.

Starch blockers are products which inhibit the digestion of starch, and so reduce its caloric value. This, in theory, could lead to reduced effective calorie intake; however, the value of these products has not been demonstrated.


No weight loss product has demonstrated the ability to induce weight loss without diet, exercise, and behavioral modification. Drug therapies also have possible side effects. Liraglutide (Saxenda) may increase the chance of developing pancreatitis and has caused a rare type of thyroid tumor in animals. In controlled studies, patients taking the drug orlistat showed increases in weight during the second year.


Pregnant or nursing women should avoid diet drugs.

Side effects

Safety is a concern when deciding to take prescription weight-loss medications and, in some cases, the side effects may outweigh the benefits. Some of the side effects of weight-loss medications are an increase in blood pressure, nausea, constipation, headaches, nervousness, heart palpitations, dry mouth, and insomnia. Depression can be another possible side effect. Those who take orlistat may have oily diarrhea that leaks from the anus.


Weight-loss drugs are used with programs of diet, exercise, and behavioral changes, such as portion control, that are intended to maintain lifetime weight goals. These behaviors must be continued after the drugs are discontinued.

Parental concerns

Although most weight-loss medications are approved only for adults, the FDA has approved orlistat for children ages 12 and older. No other weight-loss drugs have been approved for children under age 16.

See also Calories ; Ephedra ; Fen-Phen ; Green tea ; Herbalife ; Hoodia ; Obesity ; Orlistat .



Parks, Peggy J. Diet Drugs San Diego, CA: ReferencePoint, 2014.


Dong, Z., L. Xu, H. Liu, et al. “Comparative Efficacy of Five Long-Term Weight Loss Drugs: Quantitative Information for Medication Guidelines.” Obesity Reviews 18, no. 12 (December 2017): 1377–85.

Gadde, Kishore M., Corby K. Martin, Hans-Rudolf Berthoud, et al. “Obesity: Pathophysiology and Management.” Journal of the American College of Cardiology 71, no. 1 (January 2, 2018): 69–84.

Jones, Ben J., and Stephen R. Bloom. “The New Era of Drug Therapy for Obesity: The Evidence and the Expectations.” Drugs 75, no. 9 (June 2015): 935–45.

Kelly, E. M., A. A. Tungol, and L. A. Wesolowicz. “Formulary Management of 2 New Agents: Lorcaserin and Phentermine/Topiramate for Weight Loss.” Journal of Managed Care Pharmacy 19, no. 8 (October 2013): 642–54.

Kim, Gilbert W., J. E. Lin, E. S. Blomain, et al. “AntiObesity Pharmacotherapy: New Drugs and Emerging Targets.” Clinical Pharmacology and Therapeutics 95, no. 1 (2014): 53–66.

Opala, T., P. Rzymski, I. Pischel, et al. “Efficacy of 12 Weeks Supplementation of a Botanical Extract-Based Weight Loss Formula on Body Weight, Body Composition and Blood Chemistry in Healthy, Overweight Subjects— A Randomised Double-Blind Placebo-Controlled Clinical Trial.” European Journal of Medical Research 11, no. 8 (August 30, 2006): 343–50.

Shyh, Grace, and Angela Cheng-Lai. “New Antiobesity Agents: Lorcaserin (Belviq) and Phentermine/Topiramate ER (Qsymia).” Cardiology in Review 22, no. 1 (January 2014): 43–50.


Mayo Clinic Staff. “Prescription Weight-Loss Drugs.” Mayo Clinic. (accessed May 3, 2018).

MedlinePlus. “Weight-Loss Medicines.” U.S. National Library of Medicine. (accessed May 3, 2018).

National Institute of Diabetes and Digestive and Kidney Diseases. “Prescription Medications to Treat Overweight and Obesity.” National Institutes of Health. (accessed May 3, 2018).


Obesity Society, 1110 Bonifant St., Ste. 500, Silver Spring, MD, 20910, (301) 563-6526, Fax: (301) 563-6595, ., .

Office of Dietary Supplements, National Institutes of Health, 6100 Executive Blvd., Rm. 3B01, MSC 7517, Bethesda, MD, 20892-7517, (301) 435-2920, Fax: (301) 480-1845,, .

Weight-Control Information Network, National Institute of Diabetes and Digestive and Kidney Diseases Health Information Center, 9000 Rockville Pike, Bethesda, MD, 20892, (800) 860-8747,, .

Samuel D. Uretsky, PharmD
Revised by Jeanie Simoncic

  This information is not a tool for self-diagnosis or a substitute for professional care.