GLP-1 is a hormone your gut already makes after eating. These medications copy it, and hold the signal steady for a week instead of minutes. The result is that you feel full sooner, stay full longer, and think about food far less.
Your gut releases GLP-1 when you eat. It tells the brain you have had enough, tells the stomach to empty more slowly, and helps the pancreas release insulin at the right moment. Natural GLP-1 breaks down within minutes.
Semaglutide and tirzepatide are built to resist that breakdown, so one injection holds the signal for around a week. Nothing new is being added to the body. An existing signal is simply being kept switched on.
This is why the effect feels less like restraint and more like the constant negotiation with food going quiet. Most people describe it as no longer thinking about the next meal all afternoon. Semaglutide treatment covers the next part, alongside Tirzepatide treatment and What to expect.
The mechanism
In practice
How the medication works week to week
One injection a week
A small dose under the skin. The level in your blood stays steady rather than spiking and falling, which is why timing your day around it is unnecessary.
Fullness arrives earlier
Slower gastric emptying means a smaller meal now feels like enough. This is also where nausea comes from if you keep eating the old portion.
The wanting quietens
The brain signal is the part people notice most. Snacking and grazing tend to fall away before the scale shows anything.
Intake falls, weight follows
The medication does not burn fat. It reduces how much you eat, and the weight loss follows from that over months rather than days.
What it is not
What a GLP-1 does not do
It is not a fat burner and it does not change your metabolic rate in your favour. It reduces intake. Everything else follows from that, which is why the rate is measured in months.
The mechanism, the difference between molecules, and what it does not do.
They copy a gut hormone that signals fullness. Appetite falls, the stomach empties more slowly, and most people eat considerably less without consciously restricting. The weight loss follows from the reduced intake.
Semaglutide acts on the GLP-1 receptor. Tirzepatide acts on GLP-1 and GIP, a second gut hormone, and in head-to-head trials produced greater average weight loss. Which suits you is a clinical decision.
No. It does not increase how much energy you burn. It reduces how much you eat, which is a different mechanism and a slower, steadier result.
The background mental chatter about food: planning the next meal, thinking about what is in the cupboard. Many people report it quietening within the first few weeks, often before the scale moves.
Intake usually falls on its own because appetite falls. But what you eat within that smaller intake matters a great deal, particularly protein, which is why nutrition is part of the plan.
