What to Know About Weight-loss Drugs
Weight-loss drugs (or medicines) are one of the options available for people who want help with weight loss. They work in different ways and are often used alongside healthy eating and increased physical activity.
How do weight-loss drugs work?
Medicines to help with weight loss have been prescribed for many years. Weight-loss drugs work in different ways. They can:
- Decrease appetite, so you don’t feel as hungry
- Control blood glucose (sugar) by helping the pancreas make and release insulin
- Slow the emptying time of the stomach to make you feel full longer
- Work in the brain to decrease food cravings and unpleasant thoughts about eating (commonly called “food noise”)
Weight-loss drugs are grouped into different classes based on the way they work. The most common type is GLP-1 drugs, but other types may also be used for some people.
GLP-1 drugs: semaglutide, tirzepatide, and liraglutide
In recent years, newer drugs called glucagon-like peptide-1 receptor agonists (GLP-1 RAs, GLP-1 drugs, or just GLP-1s) have become available. These drugs generally are more effective and work for more people than older weight loss medicines. They have also been found to improve some chronic health conditions, like diabetes and heart disease.
These drugs work by acting like GLP-1 in the body. They activate the GLP-1 receptor on certain cells, which increases insulin levels and slows gastric (stomach) emptying. This helps lower appetite and makes you feel full for longer.
GLP-1 drugs (such as Ozempic) were originally FDA-approved to treat type 2 diabetes, but some of them are now approved for weight loss (when used along with a low-calorie diet and increased physical activity).
How it works: Activates GLP-1 receptors in the body
Year FDA approved (for weight loss): 2014
How taken: Once-a-day injection
Average weight loss: 8% of body weight
Common side effects: Nausea, vomiting, diarrhea, constipation, increased heart rate, dizziness, mood changes, fatigue, low blood glucose
How it works: Activates GLP-1 receptors in the body
Year FDA approved (for weight loss): 2021
How taken: Once-a-week injection
Average weight loss: 15% of body weight
Common side effects: Nausea, vomiting, diarrhea, constipation, abdominal (belly) pain, headache, heartburn or reflux, dizziness, mood changes, fatigue, low blood glucose
How it works: Activates GLP-1 and GIP receptors in the body
Year FDA approved (for weight loss): 2022
How taken: Once-a-week injection
Average weight loss: 20% of body weight
Common side effects: Nausea, vomiting, diarrhea, constipation, abdominal (belly) pain, heartburn or reflux, dizziness, mood changes, fatigue, low blood glucose, redness at injection site, allergic reactions
How effective are GLP-1 drugs, and how long are they taken?
Weight-loss results can vary based on the type and dosage of GLP-1 drug used. For the treatment of excess body weight, many experts recommend that these drugs be used in addition to behavioral changes that include eating a healthy diet and getting plenty of physical activity. This may also help decrease side effects that might happen when starting one of these drugs. Therapy (such as intensive behavioral therapy) can also help add to the success of treatment.
The amount of weight loss with GLP-1 drugs varies for people. Most weight loss occurs within the first year of starting one of these drugs. Weight loss slows down after the first year, and it can be harder to lose more weight.
Studies on long-term effects of GLP-1 drugs have found that some people regain weight after they stop taking these medicines. Because of this, doctors might recommend staying on these drugs (perhaps at a lower dose) long term to maintain weight loss.
Can GLP-1 drugs affect cancer risk?
It’s unclear. Researchers continue to study how weight-loss medicines might affect cancer risk. Results have been mixed so far, based on the cancer type studied.
- Some studies have suggested that the use of GLP-1 drugs might lower the risk for breast, prostate, lung, pancreatic, colon, and liver cancers, as well as basal cell carcinoma of the skin.
- In some animal studies of GLP-1 drugs, a higher risk of a rare type of thyroid cancer (medullary thyroid cancer, or MTC) has been found. Because of this, these drugs should not be used by people with a personal or family history of MTC or a rare genetic disorder called multiple endocrine neoplasia syndrome type 2 (MEN2).
Other weight-loss drugs
In addition to the newer GLP-1 drugs, there are other FDA-approved drugs that can help people lose excess body weight.
How it works: Slows or blocks the absorption of fat from foods during digestion
Year FDA approved: 1999
How taken: As a capsule by mouth
Average weight loss: 2.8–4.8% of body weight
Common side effects: Abdominal (belly) cramps, gas, oily spotting of stool, bowel incontinence (lack of self-control of stool)
How it works: Combines 2 medicines that affect chemicals in the brain to lower appetite and make you feel more full
Year FDA approved: 2012
How taken: As a capsule by mouth
Average weight loss: 5–10% of body weight
Common side effects: Dry mouth, changes in taste, constipation, mood changes, depression, anxiety, sleep problems, increased heart rate
How it works: Combines 2 medicines that help lower appetite and food cravings
Year FDA approved: 2014
How taken: As a pill by mouth
Average weight loss: 6% of body weight
Common side effects: Nausea, constipation, headache, vomiting, dizziness, sleep problems, dry mouth. Blood pressure and heart rate may increase during the first 12 weeks of treatment. Talk to your health care team about the best weight-loss drug options for you to manage your weight and have long-lasting results.
- Written by
- References
The American Cancer Society medical and editorial content team
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.
Bezin J, Gouverneur A, Penichon M, et al. GLP-1 receptor agonists and the risk of thyroid cancer. Diabetes Care. 2023; 46(2):384-390.
Brandfon S, Eylon A, Khanna D, Parmar MS. Advances in anti-obesity pharmacotherapy: Current treatments, emerging therapies, and challenges. Cureus. 2023;15(10):e46623. Published 2023 Oct 7. doi:10.7759/cureus.46623.
Caruso A, Gelsomino L, Panza S, et al. Leptin: A heavyweight player in obesity-related cancers. Biomolecules. 2023;13(7):1084.
Elmaleh-Sachs A, Schwartz JL, Bramante CT, et al. Obesity management in adults: A review. JAMA. 2023 Nov 28;330(20):2000-15. doi:10.1001/jama.2023.1989.
Ganipisetti VM, Bollimunta P. Obesity and set-point theory. [Updated 2023 Apr 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan. Accessed at https://www.ncbi.nlm.nih.gov/books/NBK592402/ on July 30, 2025.
Ibrahim SS, Ibrahim RS, Arabi B, et al. The effect of GLP-1R agonists on the medical triad of obesity, diabetes, and cancer. Cancer Metastasis Rev. Published online May 27, 2024. doi:10.1007/s10555-024-10192-9.
Khalilov R, Abdullayeva S. Mechanisms of insulin action and insulin resistance. Advances in Biology & Earth Sciences. 2023;8(2).
Lin C, et al. Comparative risk of obesity-related cancer with glucagon-like protein-1 receptor agonists vs. bariatric surgery in patients with BMI >35. Journal of Clinical Oncology. 2024; 42(16):suppl. doi.org/10.1200/JCO.2024.42.16_suppl.10508.
López M, Nogueiras R. Ghrelin. Current Biology. 2023;33(21):R1133-1135. DOI: 10.1016/j.cub.2023.09.009
Sun Y, Liu Y, Dian Y, Zeng F, Deng G, Lei S. Association of glucagon-like peptide-1 receptor agonists with risk of cancers-evidence from a drug target Mendelian randomization and clinical trials. Int J Surg. 2024;110(8):4688-4694. Published 2024 Aug 1. doi:10.1097/JS9.0000000000001514.
US Preventive Services Task Force. About prevention taskforce. U.S. Protective Services Task Force. Accessed July 30, 2025. https://www.uspreventiveservicestaskforce.org/apps/about.jsp.
Last Revised: September 9, 2025
American Cancer Society medical information is copyrighted material. For reprint requests, please see our Content Usage Policy.
More Resources
More Interactive Tools
American Cancer Society Emails
Sign up to stay up-to-date with news, valuable information, and ways to get involved with the American Cancer Society.
