The morning the number stops moving

You step on the scale and it says the same thing it said last week. And the week before. The injection went in on time, you didn't do anything different, and yet the number has parked itself. If you've been on a GLP-1 for a while, you already know the feeling that follows, and it usually arrives in this order: confusion, then the assumption that you must have done something wrong, then a quiet panic that the medicine has stopped working on you specifically.

I want to take the self-blame off the table straight away, because it's the least useful part of this and it's almost never warranted. A stall is one of the most common things that happens on these medicines, it shows up in the trial data as clearly as it shows up in your bathroom, and most of what causes it is measurable. Measurable is good. Measurable means you can look at it instead of guessing about it.

What follows is what the evidence says is going on, in the order worth checking. None of it is medical advice, and none of it is a reason to change your dose on your own. It's a way of turning "why has this stopped" into a handful of specific questions with answers.

Throughout, I'll use the generic drug names, because the brands differ by country. Tirzepatide is sold as Mounjaro in the UK, Ireland and Australia, and as Zepbound in the US. Semaglutide injection is Wegovy in all four.

First question: is it actually a plateau?

This is the unglamorous one, and it resolves a lot of stalls before anything else needs looking at. Body weight moves around by roughly one to two percent from day to day on water, glycogen, gut contents and salt alone, with nothing about your fat mass changing at all. At 90 kg that's 0.9 to 1.8 kg of ordinary noise. A fat loss of half a kilo a week is smaller than the noise it's hiding inside.

So a fortnight of flat readings genuinely can be a fortnight of losing fat while your body holds a bit more water. It happens after a salty weekend, after starting resistance training, in the week before a period, and for no visible reason at all. The way to tell the difference isn't to weigh yourself more anxiously. It's to look at a trend line over four weeks rather than any single morning.

If you want to do that check properly rather than by eye, the weight loss plateau checker walks through it: how long the trend has actually been flat, what your rate of loss was before, and which of the causes below are worth looking at in your case. It shows the figures and doesn't grade you on them.

The curve flattens in the trials too

Here's the thing that reframed this for me. A flattening curve isn't the failure mode of these medicines. It's the shape they have.

In STEP 1, the trial that put semaglutide 2.4 mg on the map, 1,961 adults were followed for 68 weeks and lost an average of 14.9% of their body weight (Wilding et al., 2021). In SURMOUNT-1, the tirzepatide trial, the highest dose averaged around 21% over 72 weeks (Jastreboff et al., 2022). Both are large, well-run trials, and in both of them the weight curve descends steeply, then bends, then runs close to flat toward the end.

That bend is not the drug wearing off. It's what happens when a system that was pushed out of balance finds a new balance. Appetite is lower, so intake is lower, so weight falls. But as weight falls, energy needs fall with it, and at some point the reduced intake and the reduced requirement meet. The curve flattening is the sound of them meeting.

Which means the honest answer to "how much will I lose" is a range, not a number, and averages hide enormous spread. Some people in those trials lost far more than the average and some lost far less, at the same dose, doing the same things. That variation is biology, and it isn't a report card.

A smaller body is cheaper to run

Two separate things are happening as you get lighter, and it's worth keeping them apart.

The first is simple arithmetic. A smaller body costs less to carry, heat and move. If you weighed 110 kg and now weigh 92 kg, the version of you climbing the stairs today is doing less work than the version six months ago. Nothing has gone wrong. There is just less of you to run.

The second is the one that catches people out, because it goes beyond arithmetic. When people lose weight and then hold the lower weight, their energy expenditure drops further than their new body size predicts. In the classic study of this, maintaining a weight 10% or more below starting weight was associated with total energy expenditure falling by 6 kcal per kg of fat-free mass per day in people who had never had obesity, and 8 kcal per kg per day in people who had (Leibel et al., 1995). For someone carrying 55 kg of fat-free mass, 8 kcal per kg works out at roughly 440 kcal a day of expenditure that the maths said should still be there.

This is called adaptive thermogenesis, and it has been documented repeatedly since (Rosenbaum & Leibel, 2010). The most quoted example is the follow-up of "The Biggest Loser" contestants: six years after the competition, resting metabolic rate was 704 kcal a day below where it started, and after adjusting for their body composition and age, 499 kcal a day of that was unexplained by size (Fothergill et al., 2016).

Two caveats, because this finding gets overstated online. That was 14 people who lost an extreme amount of weight extremely fast on television, which is not most people's situation. And in the same study, the people holding on to the most weight loss were the ones showing the most metabolic slowing, which is the opposite of the "your metabolism is broken so why bother" conclusion the internet drew from it. Adaptation is real, it's a headwind, and it isn't a wall.

The quiet gap between logged and eaten

This section is the one I'd most like to write gently, because it's true, it's important, and it's very easy to read as an accusation. It isn't one. Estimating food is a hard perceptual task that everybody is bad at, including dietitians, including me.

The reference study here took people who genuinely could not lose weight despite reporting they ate under 1,200 kcal a day, and measured what they actually ate and burned over a fortnight. Their metabolisms were normal, within 5% of predicted. What differed was the reporting: they underestimated their food by an average of 47% and overestimated their physical activity by 51% (Lichtman et al., 1992). These weren't people being dishonest. They believed their numbers.

On a GLP-1 there's a specific version of this. In the early months your appetite is so suppressed that you barely have to try, so a lot of people never build the habit of measuring. Then, months later, appetite returns a little, portions relax back toward normal, and the mental model of "how I eat now" is still based on month two. The intake has moved. The estimate hasn't.

The fix isn't to log forever or to eat less on principle. It's to measure honestly for one week, so you know where you actually are before you change anything. If the number surprises you, that's information you didn't have. If it doesn't, you've ruled out a cause and can move down the list.

Dose, time at dose, and the ceiling

Both tirzepatide and semaglutide are titrated: you start low and step up on a schedule, partly for tolerability, partly because the higher doses do more. Two things follow from that.

One, a slowdown while you're settled at a lower dose isn't the same as a slowdown at the maximum dose. They look identical on the scale and mean different things. Two, each step up tends to produce a fresh drop followed by another flattening, so the overall shape is a staircase rather than a slide.

The temptation, obviously, is to step up early, or to hold at a dose you're barely tolerating because you're afraid of losing ground. Please take both of those to your prescriber rather than deciding alone. Titration schedules exist because moving faster raises the chance of gastrointestinal side effects without a guaranteed payoff, and because the maximum dose is a maximum. What's genuinely useful is to walk into that appointment with three facts: your weight trend over the last eight weeks, roughly what you've been eating, and how long you've been at your current dose. That turns a vague conversation into a specific one.

The muscle you lost is part of the maths

Weight lost is a mixture, and the mixture matters here. Reviews of medically induced weight loss put lean mass at roughly 25 to 40% of the total lost when nothing is done to protect it (Prado et al., 2024). Muscle is metabolically active tissue, so losing a share of it lowers the energy you burn at rest, which feeds straight back into the section above.

The practical read is that protein and resistance training aren't only about how you look or how strong you are. They're part of why the floor keeps dropping out. The protein target calculator gives you the daily range for your body weight, and there's a fuller walkthrough in protecting muscle on a GLP-1.

Hunger returns before the weight does

There's one more mechanism worth naming, because it explains a stall that has nothing to do with willpower going missing. After weight loss, the hormones that govern appetite shift in the direction of eating more, and they stay shifted. A year after a diet-induced weight loss, ghrelin was still elevated and satiety hormones still suppressed compared with before, and subjective hunger was still higher (Sumithran et al., 2011).

GLP-1 medicines work against that current, which is a large part of why they work at all. But the current doesn't stop, and it can get louder over time. If food is on your mind more than it was in month two, that is a documented biological shift, not a character flaw that arrived on schedule.

What actually restarts it

In rough order of how much they tend to move the needle, and how little they cost you.

Measure before you change anything. Four weeks of weight data and one honest week of food logging tell you whether you're looking at noise, drift or a genuine stall. Changing three things at once on a hunch means you learn nothing about which one worked.

Get the protein floor back up. This is the highest-value change for most people, because it protects the tissue that sets your energy expenditure and it's the most filling macronutrient by a distance. A target beats a vibe.

Add resistance training, two or three short sessions a week. Not for the calories burned during the session, which are modest. For the signal it sends that the muscle is worth keeping.

Take the dose question to your prescriber, with data. Time at dose, tolerability and your trend are their decision to make, and they can only make it well if you bring the numbers.

Give it four weeks before judging. Fat loss is slow and body water is loud. Almost every change you make will be invisible for a fortnight, which is exactly how long most people give it.

Widen what counts as progress. Waist measurement, how clothes fit, strength in the gym, blood pressure, how you sleep. During a genuine plateau these often keep moving while the scale doesn't, because body composition is still changing underneath a stable weight.

And one thing not to do: cut your calories hard out of frustration. It tends to cost you muscle, which lowers your energy expenditure further, which makes the next plateau arrive sooner and sit lower. The stall is annoying. It isn't a reason to make the underlying problem worse.

The questions people ask

How long will this last?

Nobody can tell you, and any specific number you're given is invented. What can be said is that four weeks of flat trend is the point at which it's worth investigating rather than waiting, and that day-to-day swings of 1 to 2% of body weight are normal noise, which at 90 kg is 0.9 to 1.8 kg.

Has the medicine stopped working?

Flattening is the expected shape of these curves rather than a sign the drug has switched off. STEP 1 averaged 14.9% over 68 weeks and SURMOUNT-1's top dose averaged around 21% over 72 weeks, and both curves bend toward flat as they approach a new level. If you're genuinely worried the response has changed, that's a prescriber conversation.

Should I do a "reset" or a fasting week?

There's no good evidence that a crash week restarts a GLP-1 plateau, and there are two reasons to be careful. Very low intake on top of an already suppressed appetite makes hitting your protein target close to impossible, and rapid loss is exactly the pattern associated with a higher share of lean mass in what comes off. Talk to your prescriber before trying anything drastic.

Is a plateau a sign I've reached my body's natural weight?

Sometimes, and there's nothing wrong with that being the answer. Plenty of stalls at the maximum dose, with protein and training in place and intake honestly measured, are simply where that body has settled. If the health markers are good and you can sustain it, maintaining is a legitimate destination rather than a failure to keep going.

This is information, not medical advice. Decisions about your dose, whether to continue and what to change belong with the prescriber who knows your history. If new or severe symptoms appear alongside a stall, contact them rather than waiting for your next appointment.

If you want to see your own trend instead of guessing at it, Healthcount plots weight against doses and food in one place, so a flat fortnight is visibly a flat fortnight rather than a crisis. Start tracking free, or run the plateau checker first without signing up for anything.