GLP-1 weight loss timeline: what happens month by month

The trial averages, and what they are

Averages from trial populations receiving lifestyle support alongside the drug. They describe a group, not a person.

Two things to hold onto. First, these totals took a year and a half, not a season. Second, the spread within each trial arm is wide: some participants lost less than 5% and some lost more than 25% on the same drug at the same dose. Your own number is not predictable from the average, and comparing your month four with someone else month four tells you nothing useful about either of you.

Month one: the titration month

You start at the bottom of the ladder because starting higher causes side effects, not because the starting dose is where the effect lives. Tirzepatide begins at 2.5 mg against a 15 mg ceiling. Semaglutide begins at 0.25 mg against 2.4 mg. These are introductions.

On top of that, steady state has not arrived. It takes roughly four to five half-lives, which is about four weeks on tirzepatide and four to five on semaglutide, before the level in you stops climbing week on week. For the whole of month one you are on a rising level of a starter dose.

What people typically see is a quick drop in the first week or two, then very little. The early drop is largely glycogen and its associated water, which is a real change on the scale and not fat. When it stops, the scale flattens and it looks like the drug stopped working, at exactly the point where it has not yet started.

Months two and three: the drug arrives

This is where a normal course starts to look like the trials. You are on the second or third rung, the level is at steady state, and appetite suppression is properly present. Loss through this period commonly runs somewhere around 0.5 to 1% of body weight a week, with plenty of variation either side.

Two things characterise this phase. Every dose increase brings a fortnight of side effects before settling, so progress feels stepped rather than smooth. And food noise usually goes quiet somewhere in here, which people describe as the most striking part of the whole experience.

This is also the first point at which your data is worth analysing. Three months of weekly weights, dose dates and side-effect notes is enough to see your pattern, whereas three weeks is noise.

Months four to six: the productive stretch

Most people reach their maintenance dose in this window, either the top of the ladder or the rung where the balance of effect and tolerability is right. Loss continues at a slower absolute rate, partly because a smaller body burns less and partly because the easy early water is long gone.

Two patterns show up here that are worth recognising rather than reacting to. The first is the flat fortnight: two or three weeks with no scale movement inside a trend that is still clearly downward. The second is the real plateau, which is a longer flattening at a stable dose and a different thing entirely. Telling them apart requires a trend line, and it is impossible with daily weights and a memory.

Body composition matters more than the scale from here on. Weight that includes lean mass loss is worse than the same number of kilograms that does not, and the scale cannot tell you which you are getting.

Months seven to twelve: slower, and still going

The trials kept going to 68 and 72 weeks and the curve kept descending, more gently. In SURMOUNT-1 a substantial part of the total arrived after month six, which is the strongest argument against judging the whole course at the halfway point.

The typical late-course shape is a long slow decline with genuine plateaus in it. What tends to change is the reason for continuing: early on it is the loss, later it is holding the result, which is a different psychological task and needs different data. A twelve-month weight trend and a dose history make that visible in a way that a current number never does.

Why your curve will not look like the table

• Dose reached. Somebody who settled at 5 mg and somebody at 15 mg are not running the same experiment.
• Time at dose. Slow titration for good reasons still shifts the whole curve to the right.
• Starting point. Percentage loss and absolute loss behave differently, and both are quoted as if they were the same thing.
• Protein and resistance training. They do not change the scale much and they change what the loss is made of, which is the part that matters in year two.
• Sleep, stress, medications and menstrual cycle. All produce multi-kilogram swings on the scale that have nothing to do with fat.
• Interruptions. A supply gap or a held dose moves your timeline by more than it feels like it should. See what a late dose costs.

How to read your own numbers

1. 01 Weigh under the same conditions. Same time of day, same state, same scale. Consistency beats precision.
2. 02 Read the trend, not the reading. A weekly average against a daily number removes most of the false alarms.
3. 03 Mark every dose change on the chart. Almost everything interesting on these drugs is anchored to a dose change, and a chart without them is unreadable.
4. 04 Wait four weeks after an increase before judging it. That is how long the new steady state takes to arrive.
5. 05 Track something besides weight. Measurements, body composition, how clothes fit and how food behaves all keep moving through a scale plateau.
6. 06 Keep the whole history. The question at month nine is always what happened at month three, and nobody remembers.

This is what Penwise is built around: a trend line rather than a number, dose changes marked on it, side effects and notes attached to the weeks they belong to, and a record you can put in front of a prescriber without reconstructing it from memory.

Common questions

Sources

Every factual claim on this page traces to the product information a regulator publishes, or to a published trial. Links open on the site of whoever issued the document.

1. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1) New England Journal of Medicine, 2022
2. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1) New England Journal of Medicine, 2021
3. A Randomized, Controlled Trial of 3.0 mg of Liraglutide in Weight Management (SCALE) New England Journal of Medicine, 2015
4. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5) New England Journal of Medicine, 2025

Penwise is a tracking and education tool, not a medical device. Nothing on this page is medical advice, a diagnosis or a recommendation to start, stop or change a dose. Dosing decisions belong to you and your clinician. Ozempic, Wegovy, Rybelsus, Saxenda and Victoza are trademarks of Novo Nordisk; Mounjaro, Zepbound and Trulicity are trademarks of Eli Lilly. Penwise is not affiliated with, endorsed by or connected to either company.