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Weight Loss Medications Summary


Weight loss medication can be an important part of many individuals’ weight loss journeys. Yet, it can be confusing to navigate the many medications available on the market, all with different indications, mechanisms, and side effects. Treatment should be individualized for each patient, as the medication your doctor prescribes will depend on your medical history and treatment goals. This article will discuss the various weight loss medications available, as well as their mechanisms of action (MOA) and common side effects.

Semaglutide (Wegovy/Ozempic)

Mechanism of action

Semaglutide acts like a natural hormone found in the body known as glucagon-like peptide 1 (GLP-1) . GLP-1 helps to control blood glucose levels, which is why semaglutide is often used to treat diabetes. In addition, it can also help with cardiovascular disease and weight loss via its mechanism. To promote losing weight, semaglutide helps to curb your appetite and reduce food intake1.

Side effects

Semaglutide comes in different routes of administration, including an oral and subcutaneous form. The incidence of side effects depends on the route in which you take it. Common side effects of semaglutide are oftentimes related to the gastrointestinal (GI) system, which can include stomach pain, constipation, diarrhea, nausea, and vomiting. In addition, semaglutide can cause drowsiness and headaches2.

Liraglutide (Saxenda)

Mechanism of action

Like semaglutide, liraglutide is a GLP-1 agonist. It acts on the hypothalamus, a specific region of the brain that helps to regulate appetite and food cravings. Liraglutide helps to decrease feelings of hunger and increase feelings of satiety after a meal. Doing such helps you to eat less food, thereby promoting weight loss 3.

Side effect

Liraglutide can cause similar GI side effects to semaglutide, including constipation, diarrhea, nausea, and vomiting. It can also cause increased heart rate, headache, and low blood sugar. As it is available as a subcutaneous injection, injection-site reactions (such as redness, rash, or itchiness) can occur 2.


Mechanism of action

Phentermine plays a role in regulating hormones related to your fight or flight response, including epinephrine, norepinephrine, and dopamine. For example, phentermine acts on the central nervous system (CNS) to initiate the production of norepinephrine in the hypothalamus. Doing such helps to control your appetite. It also works via a secondary mechanism in which it helps to move fat via stimulation of the CNS and adrenal glands4.

Side effects

In terms of cardiovascular side effects, phentermine can cause increased blood pressure, an elevated heart rate, and palpitations. It can also cause anxiety, a tingling sensation in your feet or hands, trouble sleeping, and constipation2.


Mechanism of action

Vyvanase, a medication commonly used for attention deficit hyperactivity disorder (ADHD), is also FDA approved for emotional eating control. It helps with binge eating via modulating dopamine, norepinephrine, and serotonin release. As aforementioned, these neurotransmitters are involved in appetite regulation. Therefore, Vyvanse can help with overeating by controlling hunger and eating behaviors5.

Side effects

Vyvanse can cause a few GI-related side effects such as upper abdominal pain and dry mouth. Because it is a stimulant medication, it can also cause insomnia2.


Mechanism of action

Contrave consists of two drugs: naltrexone sustained release (SR) and bupropion SR. The mechanisms underlying how Contrave assists with weight loss are not entirely clear, however, the mechanism may be similar to other weight loss drugs. Studies suggest that Contrave involves pathways within the CNS, particularly regarding the hypothalamus. Via these pathways, Contrave can cause feelings of satiety, decrease one’s food intake, and increase one’s energy expenditure6.

Side effects

Contrave can cause headaches, dizziness, depression, anxiety, and impaired sleep. In terms of GI side effects, nausea is very common, but it can also cause constipation, diarrhea, vomiting, and dry mouth. Because Contrave contains bupropion, it also carries the risk of causing suicidal thoughts2.


Mechanism of action

Xenical inhibits lipases, which are enzymes in the body that break down fats found in the food you eat so that they can be absorbed in the intestines. Therefore, when you take Xenical and eat a food that has fat, it reduces the amount of fat that is absorbed into the body by roughly 30 percent. This can help with managing weight and weight loss7.

Side effects

Xenical can cause several common side effects. In terms of GI effects, it can cause gas, (sometimes with discharge), urgent or increased bowel movements, oily or fatty stools, loose stools, discolored stool, nausea, vomiting, diarrhea, and rectal and stomach pain. Xenical can also cause weakness, headache, back pain, cold symptoms, jaundice (yellowing of the eyes or skin), skin rash, itching, and teeth or gum problems2.


Mechanism of action

Like Contrave, the way that topiramate promotes weight loss is unclear. However, mice models indicate that topiramate can have an effect on how your body uses energy. This is likely due to its inhibitory effect on glutamate, a chemical found in the body. Glutamate stimulates the hypothalamus, which in turn can cause you to want to increase food intake8.

Side effects

Topiramate can cause stomach pain, nausea, diarrhea, anorexia, and problems with taste. It can also lead to fatigue, dizziness, trouble with memory, tingling or pricking sensations, low bone mineral density, fever, and upper respiratory tract infections2.


Mechanism of action

Metformin can cause weight loss primarily due to its effects on appetite regulation via the hypothalamus, thereby reducing the number of calories that you ingest. It can also cause several GI side effects, which may indirectly affect weight loss9. Additionally, metformin can also reduce body fat secondary to optimizing insulin, glucose and glycogen, thus decreasing blood sugar levels and increasing demand of fatty acids used for energy.

Side effects

Metformin primarily causes GI side effects like gas, nausea, vomiting, diarrhea, indigestion, and stomach pain. Additionally, long-term use of metformin is associated with vitamin B12 deficiency2.


Mechanism of action

Plenity is taken with a meal and then releases hydrogel particles contained within its capsule. These hydrogel particles then mix with the food you ingest, producing a larger volume of material in the stomach and intestines. With this larger volume, your body feels full and satisfied, causing you to want to eat less.

Side effects

Plenity can cause diarrhea, gas, stomach pain, and changes to your bowel habits.


  1. (n.d.). Retrieved May 9, 2022, from https://go.drugbank.com/drugs/DB13928
  2. Lexicomp (n.d.). Retrieved May 9, 2022, from https://login.ezproxymcp.flo.org/login?qurl=https://online.lexi.com%2flco%2faction%2fhome
  3. Saxenda® (Liraglutide) injection 3 mg mechanism of action. (n.d.). NovoMEDLINK. Retrieved May 9, 2022, from https://www.novomedlink.com/obesity/products/treatments/saxenda/about/how-saxenda-works.html
  4. Phentermine—An overview | sciencedirect topics. (n.d.). Retrieved May 9, 2022, from https://www.sciencedirect.com/topics/neuroscience/phentermine#:~:text=Phentermine%20is%20a%20sympathomimetic%20amine,nervous%20system%20to%20suppress%20appetite.&text=It%20has%20been%20shown%20to,with%20no%20effects%20on%20serotonin.&text=It%20is%20dosed%20up%20to,for%20short%2Dterm%20obesity%20treatment.
  5. Guerdjikova, A. I., Mori, N., Casuto, L. S., & McElroy, S. L. (2016). Novel pharmacologic treatment in acute binge eating disorder – role of lisdexamfetamine. Neuropsychiatric Disease and Treatment, 12, 833–841. https://doi.org/10.2147/NDT.S80881
  6. Ornellas, T., & Chavez, B. (2011). Naltrexone sr/bupropion sr(Contrave). Pharmacy and Therapeutics, 36(5), 255–262..
  7. Bansal, A. B., & Al Khalili, Y. (2022). Orlistat. In StatPearls. StatPearls Publishing. http://www.ncbi.nlm.nih.gov/books/NBK542202/
  8. Fox, C. K., Marlatt, K. L., Rudser, K. D., & Kelly, A. S. (2015). Topiramate for weight reduction in adolescents with severe obesity. Clinical Pediatrics, 54(1), 19–24. https://doi.org/10.1177/0009922814542481
  9. Yerevanian, A., & Soukas, A. A. (2019). Metformin: Mechanisms in human obesity and weight loss. Current Obesity Reports, 8(2), 156–164. https://doi.org/10.1007/s13679-019-00335-3
David Bauder David J. Bauder, PA-C David Bauder, PA-C, is a certified physician assistant and the assistant medical director at Weight Loss and Vitality in Manassas and Alexandria, Virginia, Washington, DC; and Gaithersburg, MD. He enjoys helping patients optimize their physical and mental health to improve their overall well-being. He earned his physician assistant degree from the University of Texas Health Science Center at San Antonio. Afterward, he gained admission into the reputable graduate program for physician assistant studies at the University of Nebraska Health Science Center in Omaha. David has over 26 years of experience working as a physician assistant. He’s practiced in podiatry, family medicine, emergency medicine, general surgery, urgent care, and functional medicine.

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