Side Effects of Weight Loss Drugs (Diet Pills)

What common or serious side effects occur with weight loss pills (diet pills)?

Some weight loss drugs are associated with important or serious side effects, or may have the potential for dependence and abuse.

  • Fenfluramine, used in the combination drug fen-phen was associated with dangerous heart and lung side effects and is no longer on the market.
  • Sibutramine was removed from the U.S. market in 2010, also due to an increased risk of serious heart side effects, including heart attack and stroke.
  • Many of the weight loss drugs known as sympathomimetic amines can stimulate the heart and lead to high blood pressure and fast heart rates (tachycardia).
  • Lipase inhibitors such as Alli or Xenical have been associated with rare liver injury and patients should be alert for signs of liver disease such as itching, yellow skin or eyes (jaundice), stomach pain, loss of appetite, pale or tar-colored stools, brown-colored urine (due to excess bilirubin in the urine).
  • Qsymia was FDA-approved as a new weight loss medication in 2012. Qsymia has a restricted-access program and a risk evaluation and mitigation strategy (REMS) because one of the drugs contained in Qsymia by the name of topiramate can lead to severe birth defects in pregnant women. Qsymia is also being investigated as a treatment for obstructive sleep apnea and diabetes.
  • Many stimulant weight loss drugs may be associated with constipation, dry mouth, restlessness, withdrawal effects, or insomnia (difficulty falling asleep).

Most weight loss medications are only recommended for short-term (up to 12 weeks) use; however, orlistat (Alli, Xenical) can be used for longer-term weight loss, including the maintenance of previously lost weight. Qsymia and Belviq are also indicated for chronic, long-term use if weight loss occurs with use of these medications.

Most people will regain some or all of the weight they lost when they stop using weight loss drugs unless efforts are made to retain their weight loss with diet and exercise.

Appetite Suppressants (anorexiants) - Side effects may include: increased blood pressure and heart rate, insomnia, nervousness, blurred vision, restlessness, or headache. Dependence, abuse or withdrawal may occur with long-term use; some forms may cause stomach side effects like constipation, dry mouth, nausea or vomiting. A healthcare provider should be contact if side effects like chest pain, pounding or rapid heartbeat, difficulty urinating, or shortness of breath occur - examples:

Lipase inhibitors - Oily spotting, gas, fecal urgency, soft stools, fecal incontinence, possibility of serious liver injury; take Alli or Xenical with a daily multivitamin that contains fat-soluble vitamins such A, D, E and K - examples:

Other weight loss drugs

  • Belviq (lorcaserin) - Headache, nausea, dizziness, fatigue, dry mouth, constipation

Common Side Effects Associated With Weight Loss Drugs

Brand Drug Name Drug Category Common Side Effects
Adipex-P (phentermine) Appetite suppressant; sympathomimetic amine Increased blood pressure and heart rate, insomnia, nervousness, restlessness, dependence, abuse or withdrawal may occur with long-term use
Alli (orlistat) - over-the-counter (OTC) only Lipase inhibitor Oily spotting, gas (flatulence), fecal urgency, soft stools, fecal incontinence; take Alli with a daily multlivitamin
Belviq (lorcaserin) Selective serotonin 2C receptor agonist (suppresses appetite) Headache, nausea, dizziness, fatigue, dry mouth, constipation; euphoria/dissociation may occur with higher doses; do not exceed 10 mg two times a day
Bontril PDM, Bontril SR (phendimetrazine) Appetite suppressant; sympathomimetic amine Increased blood pressure and heart rate, insomnia, nervousness, restlessness, dependence, abuse or withdrawal may occur with long-term use
Desoxyn (methamphetamine) Appetite suppressant; sympathomimetic amine High abuse potential; use only if alternative treatments are ineffective; increased blood pressure and heart rate, insomnia, nervousness, restlessness, dependence, abuse or withdrawal may occur with long-term use
Didrex (benzphetamine) Appetite suppressant; sympathomimetic amine Increased blood pressure and heart rate, insomnia, nervousness, restlessness, dependence, abuse or withdrawal may occur with long-term use
Diethylpropion Appetite suppressant; sympathomimetic amine Constipation, restlessness, dry mouth, Increased blood pressure and heart rate, insomnia, nervousness, restlessness, dependence, abuse or withdrawal may occur with long-term use
Qsymia (phentermine and topiramate extended-release capsules) Combination appetite suppressant-anorectic; exact action of topiramate on weight loss is not known Paresthesias, dizziness, altered taste, insomnia, constipation, dry mouth
Suprenza (phentermine) Appetite suppressant; sympathomimetic amine Increased blood pressure and heart rate, insomnia, nervousness, restlessness, dependence, abuse or withdrawal may occur with long-term use
Xenical (orlistat) Lipase inhibitor Oily spotting, gas (flatulence), fecal urgency, soft stools, fecal incontinence; take Xenical with a daily multivitamin

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See Also:

References:

U.S. Department of Health and Human Services. National Institutes of Health. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). NIH Publication No. 07–4191. Prescription Medications for the Treatment of Obesity. Accessed October 3, 2012. http://win.niddk.nih.gov/publications/prescription.htm#meds

Last updated: 2014-02-24 by Leigh Anderson, PharmD.

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