What is GLP-1? A Complete Guide to Weight Loss Injections
Medically Reviewed by
Board Certified Endocrinologist
Published
Mar 1, 2026
Last Reviewed
Mar 14, 2026
Sources
5 peer-reviewed
Standard
YMYL / E-E-A-T
Key Takeaways
- •GLP-1 medications mimic the GLP-1 hormone to reduce appetite, slow digestion, and lower blood sugar — producing 15–22% average weight loss in clinical trials.
- •FDA-approved GLP-1 drugs include Wegovy, Zepbound (for weight loss) and Ozempic, Mounjaro (for type 2 diabetes, often prescribed off-label for weight).
- •They work through 3 mechanisms: appetite suppression, slower gastric emptying, and glucose-stimulated insulin release.
- •Common side effects are gastrointestinal — nausea, diarrhea, constipation — and usually improve after the first 4–8 weeks.
- •You must have a BMI ≥ 30 (or ≥ 27 with a weight-related condition) to qualify for FDA-approved obesity GLP-1 medications.
What Are GLP-1 Medications?
GLP-1 receptor agonists are a class of prescription medications that mimic the GLP-1 hormone to reduce appetite, slow digestion, and produce significant weight loss — averaging 15–22% of body weight in clinical trials. FDA-approved options include Wegovy, Ozempic, Zepbound, Mounjaro, Saxenda, and Rybelsus. They are not appetite suppressants in the traditional sense. They work by mimicking a hormone your gut already makes: GLP-1 (Glucagon-Like Peptide-1). This changes the way your brain and digestive system communicate — the weight loss is a downstream effect of that signaling shift. Understanding this mechanism explains why they work so differently from every weight loss drug that came before.
How GLP-1 Works in the Body
When you eat, your small intestine releases GLP-1 into your bloodstream. It tells the pancreas to produce insulin (in proportion to how much glucose is actually present — not blindly, which is why hypoglycemia is rare), tells the brain you're full, and slows how quickly the stomach empties into the small intestine. The effect is that food sits in your stomach longer, you feel full on less food, and your appetite signals quiet down. Natural GLP-1 breaks down in minutes. The drug versions are chemically modified to resist that breakdown — semaglutide lasts about a week; that's why these are once-weekly injections.
Key Benefits Beyond Weight Loss
Beyond significant weight loss (often 15–20% of body weight depending on the specific medication), GLP-1 therapies offer cardiovascular benefits, improved blood pressure, better cholesterol levels, and enhanced blood sugar control. The SELECT trial demonstrated a 20% reduction in major cardiovascular events with semaglutide in people with obesity and established heart disease. Researchers are also exploring next-generation GLP-1 drugs arriving in 2026 that may push weight-loss efficacy even higher.
FDA-Approved GLP-1 Medications: Comparison Table
There are six FDA-approved GLP-1 or GLP-1/GIP medications available in the US as of 2026. Wegovy (semaglutide 2.4mg, weekly injection): approved for weight management, average 14.9% weight loss at 68 weeks, list price ~$1,350/month. Ozempic (semaglutide up to 2.0mg, weekly injection): approved for type 2 diabetes, list price ~$935/month. Zepbound (tirzepatide 2.5–15mg, weekly injection): approved for weight management, average 20.9% weight loss at 72 weeks, list price ~$1,060/month. Mounjaro (tirzepatide 2.5–15mg, weekly injection): approved for type 2 diabetes, same molecule as Zepbound, list price ~$1,023/month. Saxenda (liraglutide 3.0mg, daily injection): approved for weight management, average 5–8% weight loss, list price ~$1,400/month. Rybelsus (semaglutide 3–14mg, daily oral tablet): approved for type 2 diabetes, modest weight loss, list price ~$850/month. Tirzepatide (Zepbound) produces the highest average weight loss of any approved medication. Semaglutide (Wegovy) has the most robust cardiovascular outcomes data outside of diabetes.
Who Should NOT Take GLP-1 Medications
GLP-1 receptor agonists are contraindicated in several clinical situations. Absolute contraindications include: personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia type 2 (MEN2), as the drug label carries a boxed warning for thyroid C-cell tumors based on rodent studies; active or history of severe acute pancreatitis; pregnancy or planned pregnancy; known hypersensitivity to the medication or its excipients. Relative contraindications — conditions requiring individualized risk-benefit discussion with your physician — include diabetic gastroparesis (GLP-1 slows gastric emptying further), history of gallstones or biliary disease, severe kidney impairment, and severe liver impairment. For a complete contraindications guide, see our full article: who should not take GLP-1 medications.
How Much Do GLP-1 Medications Cost?
Cost is one of the most significant barriers to GLP-1 access. Without insurance: branded Wegovy costs $1,350–$1,600/month at retail; Ozempic runs $900–$1,080/month; Zepbound is approximately $1,060/month. With insurance: patients with good commercial coverage and a manufacturer savings card often pay $25–$50/month. For uninsured patients: the Novo Nordisk Patient Assistance Program offers Wegovy free or at minimal cost for qualifying income levels. Compounded semaglutide through telehealth platforms is available for $149–$399/month and represents the most common access pathway for uninsured patients. For a full breakdown of all payment options, see our semaglutide cost guide.
Potential Side Effects
The most common side effects are gastrointestinal, particularly when starting the medication or increasing the dose. These can include nausea, mild vomiting, diarrhea, or constipation. Most patients find these symptoms subside as their body adjusts. To understand how different formulations compare on tolerability, see our guide that compares Ozempic and Wegovy side effects head-to-head.
Who Is a Candidate?
GLP-1 therapies are typically indicated for adults with a BMI of 30 or higher (obesity), or adults with a BMI of 27 or higher with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or high cholesterol. Your physician will review your full medical history before prescribing.
Conclusion
GLP-1 medications aren't a substitute for everything else — they work best when the rest of life is also moving in the right direction. That means eating in a way that works with the medication, moving regularly, and sleeping enough. But that's different from saying "diet and exercise" in the way it's usually said to dismiss these drugs. The medications do something real that willpower doesn't: they change the biology of appetite. For most people who qualify, that combination of medical and lifestyle support produces results that neither approach achieves alone.
Frequently Asked Questions
These answers are for informational purposes only. Always consult your physician for personalized medical advice.
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Scientific References & Further Reading
- Wilding JPH et al. — Once-Weekly Semaglutide in Adults with Overweight or Obesity. NEJM 2021.
- Jastreboff AM et al. — Tirzepatide Once Weekly for the Treatment of Obesity. NEJM 2022.
- FDA Drug Approvals Database — GLP-1 Receptor Agonists. U.S. Food & Drug Administration.
- PubMed — GLP-1 Receptor Agonist Research Index. National Library of Medicine.
- Mayo Clinic — Semaglutide (GLP-1 Agonist): Uses, Side Effects, and Dosing. Mayo Clinic Drug Reference.
This content is produced in accordance with GLP-1 Health's editorial standards and is based on peer-reviewed clinical evidence from the sources cited above. It does not constitute medical advice. Always consult a licensed healthcare provider before starting any medication.
Continue Your GLP-1 Research
GLP-1 Medications: Complete 2026 Comparison Guide (Wegovy, Ozempic, Zepbound, Mounjaro)
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Ozempic vs Wegovy: Which GLP-1 is Right for You?
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Who Qualifies for GLP-1 Injections? BMI Thresholds, Medical Criteria, and the Gray Areas
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