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Last updated January 21, 2020. 4 minute read

Weight loss pills—6 are FDA approved. This is how they work

There are currently six weight-loss medications approved by the FDA: phentermine, phentermine/topiramate, liraglutide, lorcaserin, naltrexone/bupropion, and orlistat. Weight-loss medications, in addition to diet, exercise, and lifestyle modifications, are appropriate for some people to help with their weight loss goals.

Dr Chimene Richa Md Written by Dr. Chimene Richa, MD
Reviewed by Dr. Tzvi Doron, DO

Being overweight or obese is more than just not fitting into your clothes; they are chronic medical conditions that affect many people worldwide. In the United States, over 71% of adults over the age of 20 are classified as overweight or obese; that’s more than two out of every three adults (CDC, 2016). Obesity is determined by using a person’s Body Mass Index (BMI); this is a measurement of your body weight in kilograms (1 kilogram equals 2.2 pounds) divided by your height in meters squared (1 meter equals ~3 feet 3 inches). You can easily calculate your BMI by clicking here. Using your BMI, you can determine which of the following categories applies to you:

  • Normal weight: BMI of 18.5 to 24.9 kg/m2 
  • Overweight: BMI of 25 to 29.9 kg/m2 
  • Obesity: BMI of 30 kg/m2 or higher 

Being overweight or obese increases your risk of several health conditions, including heart disease, stroke, and diabetes. Losing as little as 5-10% of the excess weight can significantly improve your health. Weight-loss medications, in addition to diet, exercise, and lifestyle modifications, are appropriate for some people to help with their weight loss goals.

Vitals

  • Overweight and obesity are chronic medical conditions that affect over 71% of adults in the United States.
  • Overweight is defined as having a BMI of 25-29.9 kg/m2, and obesity is a BMI of 30 kg/m2 or higher.
  • There are currently six weight-loss medications approved by the FDA: phentermine, phentermine/topiramate, liraglutide, lorcaserin, naltrexone/bupropion, and orlistat.
  • Weight-loss drugs work best when combined with diet, exercise, and other lifestyle modifications.

What are weight-loss medications?

Weight loss drugs work in different ways. Some act as an appetite suppressant (decrease your desire to eat) while others decrease how much fat you absorb from the foods you eat. Medications for weight loss are indicated for the following people:

  • A BMI of 30 kg/m2 or more
  • A BMI of 27 kg/m2 or more with a weight-related health problem, like high blood pressure, type 2 diabetes, or heart disease.

There are currently six medications approved by the Food and Drug Administration (FDA) to treat weight loss with a wide range of responsiveness to these treatments (NIDDK, 2016). None of these drugs should be used in women who are pregnant, trying to become pregnant, or breastfeeding.

  • Phentermine: This drug decreases your appetite and is only approved for short-term use, up to 12 weeks. It is a stimulant and considered a “scheduled” drug by the Drug Enforcement Administration (DEA); this means that there is some potential for abuse.  
  • Phentermine/topiramate (brand name Qsymia): This is a combination of phentermine and the anti-seizure drug, topiramate; using both drugs together works better than either drug alone to reduce appetite. Because of the potential for abuse, it is considered a scheduled drug by the DEA. 
  • Liraglutide (brand name Saxenda): This injectable drug is part of a class of drugs called GLP-1 agonists, most commonly used to treat type 2 diabetes. It makes you feel less hungry or full sooner
  • Lorcaserin (brand name Belviq): Lorcaserin works by activating a specific serotonin receptor (5-HT2C receptor) in the brain to promote a feeling of fullness (satiety) after eating smaller amounts of food. Because of the potential for abuse, it is considered a scheduled medication by the DEA. 
  • Naltrexone/bupropion (brand name Contrave): Naltrexone is used to treat drug and alcohol dependence. Bupropion is used to treat depression and help people quit smoking. The combination helps you to feel less hungry and to promote a feeling of fullness after eating smaller amounts of food. 
  • Orlistat (brand names Xenical, Alli): This drug works by decreasing the amount of fat from your food that is absorbed by the digestive system. It is available in prescription strength (brand name Xenical) and a lower non-prescription (brand name Alli) strength. 

All of the above medications are considered effective at helping people achieve at least 5% weight loss at one year; phentermine-topiramate and liraglutide had the highest odds of achieving this goal (Khera, 2016).

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Are there potential side effects of weight loss medication?

Before starting any prescription treatment program, talk to your healthcare provider about the risks and benefits. Below is a summary of some of the potential side effects of the FDA-approved weight-loss drugs (NIDDK, 2016).

  • Phentermine
    • Dry mouth, constipation, difficulty sleeping, headaches, dizziness, nervousness, restlessness, increased blood pressure, faster pulse
  • Phentermine/topiramate
    • Constipation, dizziness, dry mouth, taste changes (especially with carbonated beverages), tingling of hands and feet, difficulty sleeping
  • Liraglutide
    • Nausea, diarrhea, constipation, abdominal pain, headache, faster pulse
  • Lorcaserin
    • Constipation, cough, dizziness, dry mouth, feeling tired, headache, nausea
  • Naltrexone/bupropion
    • Constipation, diarrhea, dizziness, dry mouth, headache, increased blood pressure, faster pulse, difficulty sleeping, liver damage, nausea, vomiting
  • Orlistat
    • Diarrhea, gas, leakage of oily stools, stomach pain

Do weight loss medications replace diet and exercise?

Absolutely not! Nothing can replace exercising and healthy diet choices with regards to your health and weight loss. In fact, weight loss medications work better when combined with a healthy diet and lifestyle changes. According to the US Preventative Services Task Force (USPSTF), treating obesity with drugs should only be used as a part of an overall program that also includes lifestyle modifications, like diet and exercise, counseling, and behavioral interventions (USPSTF, 2004). People taking weight loss medications along with lifestyle modifications lose, on average, 7% to 10% of their initial weight at one year; this may improve your risk of multiple health problems like type 2 diabetes and high blood pressure (Yanovski, 2014).

In conclusion…

Weight-loss medications may be the added boost that you need to help you lose weight; however, they are not for everyone. Talk to your healthcare provider about your options for losing weight with prescription medications to see if any are right for you. Remember that weight loss is most successful and sustainable if you combine it with lifestyle changes, like a healthier diet and increased exercise.