How Do Weight Loss Injections Work?
A simple guide to the science behind GLP-1 medications like Wegovy and Saxenda.
What is GLP-1?
GLP-1 (Glucagon-like peptide-1) is a hormone naturally produced in your gut after you eat. It plays a key role in regulating your appetite and blood sugar levels.
However, natural GLP-1 breaks down very quickly in the body (within minutes). Weight loss injections contain GLP-1 receptor agonists, which mimic the hormone but last much longer (hours or days).
The 3 Main Mechanisms
1. Signals Your Brain to Stop Eating
The medication travels to the hypothalamus in your brain—the area that controls hunger. It signals that you are full, reducing your appetite and cravings.
2. Slows Down Digestion
It slows the rate at which your stomach empties food into your small intestine (gastric emptying). This means you feel physically fuller for longer after meals.
3. Regulates Blood Sugar
It helps your pancreas release the right amount of insulin when blood sugar levels are high, which is why these medications were originally developed for type 2 diabetes.
What About Mounjaro?
Mounjaro (Tirzepatide) is unique because it mimics TWO hormones: GLP-1 and GIP (Glucose-dependent insulinotropic polypeptide).
This dual action is believed to enhance weight loss results even further compared to single-hormone medications like Wegovy.
Read more about GLP-1 vs GIP →Medical References & Sources
- Mechanisms of Action of GLP-1 Receptor Agonists - Diabetes Care
- Semaglutide for Weight Management - NEJM
Last Medically Reviewed: April 2026