What semaglutide actually does to your appetite
No magic and no detox. The mechanism, the trial numbers, and the part where it stops working if you stop.
After you eat, your gut releases a hormone called GLP-1. It does three jobs. It tells your pancreas to release insulin. It slows down how fast your stomach empties. And it tells the appetite centres in your brain, the hypothalamus and the brainstem, that food has arrived.
Natural GLP-1 lasts about two minutes in your blood before an enzyme chews it up. Semaglutide is GLP-1 with a few changes that stop that enzyme and let it ride on a blood protein called albumin. Result: a half-life of roughly seven days. One injection a week keeps the signal on.
What that feels like
People describe it the same way, over and over: the food noise goes quiet. You stop thinking about the next meal while eating this one. Portions shrink without negotiation. Fried things and sweet things lose some of their pull, because GLP-1 also turns down the reward response to food.
The stomach part is real too. Food sits longer, so you feel full sooner. It is also where most of the side effects come from.
The drug does not burn fat. It makes eating less feel normal instead of feeling like a fight.
The numbers, from the actual trials
STEP-1 followed 1,961 adults with obesity for 68 weeks on 2.4 mg a week. Average loss was 14.9% of body weight, against 2.4% on placebo.1 For someone at 110 kg, that is roughly 16 kg.
In a scan substudy, close to 40% of what people lost was lean mass, not fat.2 That is why we push protein and resistance training from week one. Skinny-fat is a real outcome if you ignore this.
The side effects nobody puts in the ad
In STEP-1, 74% of people on semaglutide reported a gut side effect, mostly nausea, diarrhoea, constipation and vomiting. Most of it was mild and faded, and it clusters in the days after each dose increase.1 That is why we titrate slowly: 0.25 mg for four weeks, then step up.
Rarer, more serious: gallbladder problems, pancreatitis, and a thyroid tumour signal seen in rodents. If you or a family member has had medullary thyroid cancer or MEN2, this is not for you. Our intake asks.
What happens when you stop
In the STEP-1 extension, people who stopped regained about two-thirds of what they had lost within a year.3 Semaglutide treats appetite while you take it. It does not reset it. Plan the exit before you start: a maintenance dose, a slow taper, or habits strong enough to hold the line.
- Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). NEJM 2021;384:989–1002.
- STEP 1 DXA substudy, reported in the same paper's supplementary appendix.
- Wilding JPH et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide. Diabetes Obes Metab 2022;24:1553–64.
