The first 3 months on a GLP-1: what the dose steps are for, and what's worth writing down

The first few weeks on a weight-loss injection or tablet can feel like a lot of waiting. You start on a dose lower than the one you'll be on later, you're watching for side effects, and everyone online seems to have a number for what you "should" see by month three.

I want to deal with that number first, because it doesn't exist in the way people think. What the first 3 months are really about is getting used to the medicine, one dose step at a time. So that's what this page covers: why the steps are there, what people commonly notice, what's worth writing down, and when to speak to your GP or prescriber.

Why the first 3 months are mostly dose steps

Both medicines start low and go up slowly, and the prescribing information (the SmPC) says why. Wegovy's says the dose is increased over 16 weeks "to reduce the likelihood of gastrointestinal symptoms". Mounjaro's says nausea, diarrhoea and vomiting happened mainly while the dose was going up, and eased over time.

So at week 12, people are partway up the ladder. Here's the fastest each SmPC allows.

That's the fastest pace, not a plan for you. Your prescriber sets your doses and may keep you on one for longer. The Wegovy SmPC says that with significant stomach symptoms, the prescriber can consider delaying the next step, or going back to the previous dose until things settle. Wegovy's 7.2 mg dose, where it's used, comes after at least 4 weeks on 2.4 mg. Our Mounjaro dose chart has the details for Mounjaro.

What the trials can and can't tell you about month 3

The trials behind these medicines were long. Mounjaro's main weight trial, SURMOUNT-1, ran for 72 weeks. Wegovy's, STEP 1, ran for 68 weeks, and the main trial of the tablets for 64. Everyone in them, on the medicine or on placebo, also had advice on eating and activity.

Their main results are averages at the end, after people had spent most of a year or more on their full dose. The weeks before that are shown only as a line on a chart, and neither main trial report gives an average for 3 months. If you see one online, it's someone's reading of that chart, or a figure from a different trial.

So I'm not going to give you a number. Partly because there isn't a published one, and partly because an average hides a huge spread between people. Yours is yours.

One more thing from the research, because it comes up a lot. A later analysis of SURMOUNT-1, paid for by Lilly, looked at the people whose weight had changed least by week 12. Most of them saw it change later in the trial. That isn't a reason to change anything yourself. It's a reason not to read too much into month 3.

The 6-month review

Here's something the UK does that I find quite reassuring. For both injections, NICE's guidance and the SmPCs set the first formal review at 6 months, not 3. That's when you and your prescriber decide together whether to carry on. For Mounjaro, the 6 months count from when you reach the highest dose you can manage, so the review comes later than 6 months from your first dose.

NICE's guidance is written for the NHS, where Wegovy is prescribed through a specialist weight management service. Private prescribers may work differently, so it's worth asking at the start how and when yours will review things.

What people commonly notice

Appetite

Most people notice their appetite first. These medicines slow down how quickly your stomach empties, so you may feel full sooner and stay full for longer. Some people find food takes up less of their thinking. Others find the change odd, or a bit unsettling, especially if eating has been complicated for them before. Both are worth writing down.

Side effects

The SmPCs list the stomach and gut ones as the most common: nausea, diarrhoea, vomiting, constipation, tummy pain, indigestion and burping. Tiredness and hair loss are listed too. They tend to show up while the dose is going up, which is exactly why the first 3 months are worth keeping track of. Our side effect timeline shows when they usually peak and settle.

How meals change

Portions often get smaller without you deciding they should. Some meals sit heavily, some foods you used to enjoy don't appeal for a while, and on some days nothing sounds good. None of that needs fixing, but it's useful to notice which meals felt comfortable and which didn't.

Eating and drinking enough

With a smaller appetite, it's easy to go a long time without eating, or to forget to drink. The SmPCs warn that being sick and diarrhoea can lead to dehydration, which can affect your kidneys, so fluids matter most on the days you feel unwell. Eating regularly matters too, even if the meals are small. Our piece on regular eating explains why.

If you take the contraceptive pill

The MHRA says that if you take Mounjaro and the pill, you should add a barrier method, such as condoms, for 4 weeks after starting and for 4 weeks after any dose increase. That covers most of the first 3 months, so it's worth raising with your prescriber at the start.

What's worth writing down

You don't need to write everything down. A few lines a day is plenty, and it gives you something real to take to your next appointment, instead of trying to remember how week 5 went.

Weighing yourself is optional. You don't need to step on the scales to keep a record that's useful to you and your prescriber.

How a food journal helps

Why bother writing it down? Mostly because memory isn't reliable, especially across weeks of small changes. A written record lets you spot patterns, like nausea that turns up the day after a dose step, or a meal that never sits well. It also lets your prescriber see what actually happened rather than what you remember, which matters all the more with a review at 6 months. There's a fair amount of research on food diaries, and our piece on why writing it down works goes through it.

If you want somewhere to keep it, Healthcount is a free food journal. You write meals in your own words, add your doses and how you feel, and the numbers are optional. A notebook works too. The point is the record, not the app.

When to speak to your GP or prescriber

Your prescriber would rather hear from you early than late. Get in touch:

• if side effects are making it hard to eat or drink, or you're not sure you're ready for the next dose step
• if you've missed a dose and aren't sure what to do. Each medicine has its own rule, and your pharmacist can help too
• before an operation or a procedure with sedation
• if anything else worries you, even if it seems small

You can report a side effect through the MHRA's Yellow Card scheme.

Frequently asked questions

General information from the UK prescribing information, NICE and the MHRA, checked 21 October 2026. It isn't medical advice. Your prescriber decides whether a medicine is right for you, which one, and every dose. Prescribing information changes, so check the current leaflet with your pharmacist.