How GLP-1 medicines work

GLP-1 is a gut hormone released after food

GLP-1 stands for glucagon-like peptide-1. Your gut releases this hormone when you eat. A receptor is a structure on a cell that receives a chemical message. An agonist switches the receptor on. GLP-1 receptor agonists are medicines built to keep part of this system switched on for longer than the natural hormone does.

They help the pancreas release insulin when blood glucose is high. They also cut back glucagon signalling when the body does not need it. Glucagon is a hormone that releases stored glucose. These actions explain why people first knew the class as a type 2 diabetes treatment. GLP-1 medicines are not insulin, though. Never use one as an automatic replacement for prescribed insulin.

Effects on appetite and digestion

Some GLP-1 medicines reduce appetite and food intake, so smaller portions feel satisfying. They can also slow the rate at which your stomach empties. Not every symptom comes from food sitting in the stomach, and slower digestion does not account for the whole effect.

People notice different things. One person snacks less. Another first notices smaller meals. Some feel sick without much change in appetite, and others do well with few side effects. Feeling unwell does not prove the medicine is working. If you cannot eat for days at a time, ask for a review. Not eating is never the goal.

Semaglutide, liraglutide and tirzepatide differ

Semaglutide and liraglutide act on the GLP-1 receptor. Tirzepatide acts on both the GIP and GLP-1 receptors. "GLP-1 medicines" is a handy label, but the medicines differ in active ingredient, formulation, dose, how you take them and what they are licensed for.

One active ingredient can sit in products licensed for different uses. A diabetes product and an obesity product may follow different dose schedules even when both contain semaglutide. You also cannot convert a tablet dose to an injection dose with a simple milligram ratio. Absorption and the way each product delivers the ingredient change the numbers.

Questions to ask about any treatment claim

When you read about treatment, check which medicine, formulation, dose and condition the writer means. A strong trial result for one product does not carry over to another. Heart outcome evidence in a defined group does not mean everyone on the class is protected.

In a consultation, say what you want treatment to improve. You might want better glucose control, easier movement, lower weight-related health risks or another agreed goal. Then ask how the medicine supports that goal and how you will measure progress. The talk then moves from appetite hormones in general to one treatment for you.

Record the brand, ingredient and formulation together

Write the brand, active ingredient and formulation side by side in your records. "Semaglutide" on its own does not tell a new doctor whether you take a tablet or an injection. Add the strength and the schedule you follow.