GLP-1: what it is and how it works for weight loss

What is GLP-1?

GLP-1 is an incretin hormone. Special cells in your gut wall release it as soon as food arrives. The hormone travels through your blood and sets several things in motion at once: the pancreas makes more insulin, the liver releases less sugar, your stomach passes food on more slowly, and in your brain the feeling of fullness is switched on.

Your own GLP-1 is broken down again within a few minutes. That is exactly the difference with the medicines: they are built to last much longer, from a day to a week. So the signal that you have had enough stays on, including at moments when your body no longer gives it by itself.

In the consulting room and in the news you hear different names used side by side: GLP-1, GLP-1 agonist, GLP-1 receptor agonist, incretin mimetic. They all refer to the same principle. GLP-1 is the hormone, the rest are the medicines that mimic it.

How do GLP-1 agonists work?

Four effects at once, and they reinforce each other. That explains why these medicines work differently from earlier weight-loss medication, which usually pressed a single button.

How strong each effect is differs per medicine and per person. Some medicines also act on other hormone receptors, which makes the picture different for each one.

Which GLP-1 medicines exist?

Below are the medicines people ask about most in the Netherlands. They differ in active substance, in how they are taken and in what they are licensed for. A licence for type 2 diabetes does not mean a medicine is also approved for weight treatment, and the other way round.

Whether a medicine suits you depends on your health, your medical history and the medicines you already take. That judgement is made by a doctor, not by a comparison table.

Injection or tablet?

Most GLP-1 medication is an injection, and there is a reason for that. Semaglutide and liraglutide are proteins. Your stomach juices break proteins down, so in tablet form almost nothing reaches your blood without added excipients.

So the oral version is not a weaker one, it is a different way of taking the medicine with conditions of its own. If you want to see them side by side, the full comparison is on the page about oral GLP-1 medication.

What can you realistically expect?

GLP-1 treatment always starts low and is built up step by step. That is not caution for the sake of caution, it is how side effects are kept manageable. Broadly, it runs in four phases.

1. Week 1 to 4

   Starting up

   You begin on the lowest dose. That dose is not there to make you lose weight but to let your body get used to it. Most stomach and bowel complaints come up in these weeks and often ease off afterwards.

2. Month 2 and 3

   Building up

   The dose goes up step by step, and only if the previous step went well. If you have complaints, you stay on a step longer or go back a step. The effect on your appetite becomes clearer in this period.

3. Month 4 to 6

   Maintenance

   You are on a dose that fits. What the medicine does for you can now be judged properly. This is also the point at which it becomes clear whether the treatment is having the desired effect.

4. After that

   Keeping it up

   Obesity is a chronic condition and GLP-1 medication treats it for as long as you take it. If you stop, in most cases your appetite comes back and often some of the weight too. What you build up in the meantime in habits, muscle mass and exercise determines how much you hold on to.

Side effects and risks

GLP-1 agonists are not harmless medicines. They are prescription only, and there is a reason for that. Most side effects are mild and temporary, but there are situations in which you contact a doctor straight away.

Beyond side effects, keeping muscle matters. With rapid weight loss, part of what you lose can be muscle rather than fat. Enough protein and strength training during treatment limit that, and with good guidance the loss usually stays confined to fat. The full list of side effects is in each medicine’s official leaflet.

Who is GLP-1 medication meant for?

These medicines are licensed for specific situations. They are not meant for people who want to lose a few kilos, and a doctor will not prescribe them for that either.

This is a shortened version. A doctor weighs up your full medical situation, including the medicines you already take.

Is GLP-1 medication reimbursed?

Sometimes. For type 2 diabetes there is a reimbursement scheme with conditions attached. For weight treatment, reimbursement is limited to a small group and strict criteria apply, including a combined lifestyle intervention that has been completed first.

In practice, most people who use these medicines for weight treatment pay for them themselves. Conditions also change from year to year, so check your policy and the current scheme with your health insurer.

Frequently asked questions about GLP-1

The questions we get asked most, in the words people use to ask them.