GLP-1 receptor agonists have become the most significant advance in weight loss medicine in decades, consistently producing 15–20% total body weight reduction in clinical trials — results previously achievable only with bariatric surgery. But many patients starting these medications have only a vague understanding of how they work. This primer explains the science clearly so you can be a more informed participant in your physician-supervised weight loss program.
What Is GLP-1?
GLP-1 stands for glucagon-like peptide-1, a hormone naturally produced by cells in your small intestine in response to food intake. In your body, GLP-1 performs several important roles: it stimulates insulin secretion from the pancreas when glucose is present (glucose-dependent insulin release), suppresses glucagon (which raises blood sugar), slows gastric emptying (keeping food in your stomach longer), and critically — it acts on receptors in your brain, particularly in the hypothalamus and brainstem, to reduce appetite and increase the feeling of fullness.
The problem with naturally secreted GLP-1 is that it has a half-life of just 2–3 minutes, rapidly broken down by an enzyme called DPP-4. Pharmaceutical GLP-1 receptor agonists like semaglutide are engineered to resist this degradation, maintaining GLP-1-like activity for days to weeks after a single injection.
Semaglutide vs. Tirzepatide: The Key Difference
- Semaglutide (Ozempic, Wegovy): A GLP-1 receptor agonist — activates GLP-1 receptors only
- Tirzepatide (Mounjaro, Zepbound): A dual GIP/GLP-1 receptor agonist — activates both GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors simultaneously
- The dual-action mechanism of tirzepatide appears to produce greater weight loss (20–22% average in SURMOUNT trials vs. 15% for semaglutide in STEP trials)
- Both are weekly subcutaneous injections; both are highly effective
Starting a Physician-Supervised GLP-1 Program
Understanding the mechanism helps explain why titration matters (lower starting doses minimize side effects while letting the brain adjust), why dietary modifications amplify results, and why stopping the medication leads to weight regain. Dr. Arpana Pillay at Vish Medical prescribes and manages GLP-1 therapy as part of comprehensive weight loss care. View our program pricing or book your consultation.