The weight-loss jab works. That's the problem.

Let me start with a confession that might get me uninvited from a few gym WhatsApp groups: the weight-loss jab works.

Not “kind of works”. Not “works if you believe in it”. It works. The newest drugs in trials are producing close to 30% average weight loss — results that used to need surgery.

And that is exactly the problem. When something works this well, people stop asking what they are losing, and what happens next. If you are a busy professional who has been tempted by the jab (or the new pills), this one is for you. Grab a coffee. Preferably one you walked to.

First, what are GLP-1s?

GLP-1 is a hormone your gut releases after you eat. It tells your brain “we’re good, stop eating”, and it slows down how fast your stomach empties. GLP-1 drugs copy that signal, so you feel full sooner and stay full longer. The constant food noise goes quiet.

This is what is on the table in 2026:

Option	Type	Average weight loss in trials
Semaglutide (Wegovy)	Weekly injection	About 15%
Tirzepatide (Mounjaro)	Weekly injection	About 21% after 36 weeks
Orforglipron (Foundayo)	Daily pill, approved in the US in April 2026	About 11%
Retatrutide	Weekly injection, still in trials	About 28% after 80 weeks

The pills are more convenient but weaker; the injections are stronger. So far, so impressive. Now for the fine print nobody puts on the box.

Problem 1: not everything you lose is fat

Depending on the study, between 25% and 40% of the weight lost on GLP-1s is lean mass. In the big semaglutide trial, STEP-1, it was roughly 40%. Lean mass is not only muscle — it also counts water and organ tissue — but muscle is a large part of it.

Put simply: of every 10 kg that comes off, up to 4 kg may not be fat.

Why that matters: muscle is not just for the mirror. It keeps your metabolism up, protects your joints, helps control your blood sugar and keeps you strong as you age. From your forties onwards you lose some muscle every decade anyway, unless you train it. Adding drug-driven muscle loss on top is like taking money out of your pension to pay for a holiday.

The scale goes down. The mirror says “smaller”. But underneath, you may have swapped a bigger version of you for a softer, weaker one.

Problem 2: stop the drug, and the weight comes back

These drugs work while you take them. Stop, and your appetite comes back like a colleague returning from holiday: loud, hungry, and with stories.

A 2026 Oxford meta-analysis in The BMJ pooled 37 studies and more than 9,000 people. After stopping semaglutide or tirzepatide, people regained about 0.8 kg a month, and were projected to be back at their starting weight in about a year and a half. In the first year alone, the average regain was 9.9 kg. That is about four times faster than after a behavioural weight-loss programme, where people build habits instead of borrowing them.

The health benefits fade too: improvements in blood pressure and blood sugar largely return to where they started.

In fairness, real life can look kinder. A Cleveland Clinic study of nearly 8,000 patients found people regained only 0.5% of their body weight in the year after stopping — but many of them restarted the drug or switched to another treatment. Either way, the message is the same: without a plan, the weight has a return ticket.

Problem 3: in Belgium, you pay for it yourself

In June 2026, health minister Frank Vandenbroucke decided not to reimburse Wegovy for weight loss. He followed the advice of RIZIV’s medicines committee and pointed to the cost, which could run into billions of euros a year if every eligible patient were treated.

France went the other way: from 15 June 2026, Wegovy and Mounjaro are covered at 65% for severe obesity, under strict conditions. In Belgium, GLP-1 drugs are still reimbursed for type 2 diabetes, but since February that needs prior approval from your health insurer. For weight loss alone, it comes out of your own pocket.

So here is the uncomfortable maths: you could be paying every month to lose your own muscle — and then pay again, in kilos, when you stop.

And please don’t go looking for a cheaper source online. Belgium’s Poison Control Centre has reported a rise in calls about overdoses of these drugs. Get them prescribed, and get them monitored.

The plot twist: same drug, a different body

Here is where it gets interesting. In a 2025 study presented at the European Congress on Obesity, 200 adults on semaglutide or tirzepatide were also taught how to do resistance training and how much protein to eat. After six months they had lost 12–13% of their body weight — and about 1 kg of muscle, or less.

On paper, that is far less than the 25–40% lean-mass loss in the earlier trials, although the two were measured differently. The drug was the same. What changed was the barbell and the plate.

This is early evidence: the study had no comparison group, and as of May 2026 no randomised controlled trial had tested resistance training specifically as the answer to GLP-1 muscle loss. But it fits everything we already know about losing weight well — lift, eat enough protein, and more of what you lose comes from fat.

The jab isn’t the shortcut. The habits are.

The medicine turns down the hunger. It does not build muscle, it does not teach you to cook, and it definitely will not walk to the coffee machine for you.

The playbook, if you’re on a GLP-1 or thinking about it

You work nine to five. Some days, nine to nine. Here is the short version.

1. Strength train at least three times a week. Cover all the major muscle groups, and start in the first weeks of treatment — not after the muscle has already gone. Forty-five minutes is plenty. If you are new to lifting, have someone check your technique first.
2. Eat protein at every meal. A common target while losing weight is about 1.2–1.6 g per kg of body weight a day; if you are carrying a lot of extra weight, work it out from your goal weight instead. On a small appetite that means protein first: eggs, Greek yoghurt, chicken, fish, tofu, lentils, a shake if you must. If you have kidney problems, agree your target with your doctor.
3. Track more than the scale. Measure your waist, take photos and, ideally, get a body-composition scan. If your strength is dropping, that is a warning sign, not a win.
4. Keep moving through the day. Walk after lunch, take the stairs, stand on calls. The drug will not do your step count for you.
5. Have an exit plan before you need one. Agree with your doctor how and when you will come off the drug, and use the time on it to build the habits that keep the weight off without it.

Think of the jab as stabilisers on a bike. Helpful to get going — but at some point, you have to learn to ride.

The bottom line

GLP-1 drugs are a genuine breakthrough, and for many people with obesity they can be life-changing. I am not here to shame anyone for using them.

But the needle can only start the journey. Making it stick is the part you do yourself — and that is exactly what I help busy professionals with: strength training that fits around a full-time job, protein you will actually eat, and a plan for life after the jab.

This article is general information, not medical advice. Decisions about starting, dosing or stopping any medication belong with your doctor. Muscles belong with you.