Why is my starting dose so low?

The starting dose (Mounjaro 2.5 mg, Wegovy 0.25 mg) is to let your body get used to the medicine, not the dose that does most of the work. You step up over the following weeks. Starting low and increasing slowly is what keeps the side effects manageable.

How soon will it start to work?

The Mounjaro leaflet says it lowers hunger from the first week and increases fullness from week 3. Weight loss then builds over the following weeks and months as the dose steps up. Wegovy has a fixed 16-week step-up, and the steepest weight loss usually comes once you reach the maintenance dose. How fast anyone loses weight varies a lot.

Is it normal to feel sick in the first weeks?

Yes. The leaflets say nausea, diarrhoea and being sick happen mostly during the dose step-up and ease over time, and are mild or moderate for most people. Smaller meals and going easy on fatty or sugary food help. See the side effects guide for more.

What to expect in your first month on Mounjaro or Wegovy

The first month is about easing in, not full effect. You start on a low dose, the appetite effects can come early, and the side effects are most likely during the step-up. Here is the shape of it, from the UK leaflets.

Last updated 3 November 2026

The short version

You start low (Mounjaro 2.5 mg, Wegovy 0.25 mg) and step up. The starting dose is not the dose that does the work.
Appetite effects can come early; steady weight loss builds over weeks and months.
Side effects are most likely during the step-up, then settle.
Follow the schedule your prescriber set, and never change the dose yourself.

You start low and step up

Both medicines begin on a low starting dose that is there to let your body adjust, then increase over the following weeks. For Mounjaro you start at 2.5 mg and reach the first full dose, 5 mg, at week 5. Wegovy follows a fixed 16-week step-up to its 2.4 mg maintenance dose. Map your own dates with the Mounjaro or Wegovy dose schedule.

When it starts to work

The Mounjaro leaflet says it lowers hunger from the first week and increases fullness from week 3, so many people notice the appetite effect early even though the dose is still low. The weight loss itself builds over the weeks and months as the dose steps up, and the steepest part usually comes once you are on the full maintenance dose. How fast weight comes off varies a lot from person to person. For the detail, see how long it takes to work.

Side effects in the first weeks

The first month is also when side effects are most likely, because they come mainly with each dose increase. The common ones are stomach related, nausea, diarrhoea, constipation and being sick, and the leaflets say they are mild or moderate for most people and ease over time. What helps, and the serious signs to act on, are in the side effects guide.

Getting the practical bits right

Injecting: same day each week, and if the pen gives trouble see pen troubleshooting.
Storing it: fridge, and the in-use window once opened. See how to store your pen.
Eating: smaller meals, enough protein and fluids, and go easy on fatty or very sugary food, which worsens nausea.
Reporting: tell your prescriber about anything troubling, and report side effects on the Yellow Card scheme.

Common questions

Why is my starting dose so low?: The starting dose (Mounjaro 2.5 mg, Wegovy 0.25 mg) is to let your body get used to the medicine, not the dose that does most of the work. You step up over the following weeks. Starting low and increasing slowly is what keeps the side effects manageable.
How soon will it start to work?: The Mounjaro leaflet says it lowers hunger from the first week and increases fullness from week 3. Weight loss then builds over the following weeks and months as the dose steps up. Wegovy has a fixed 16-week step-up, and the steepest weight loss usually comes once you reach the maintenance dose. How fast anyone loses weight varies a lot.
Is it normal to feel sick in the first weeks?: Yes. The leaflets say nausea, diarrhoea and being sick happen mostly during the dose step-up and ease over time, and are mild or moderate for most people. Smaller meals and going easy on fatty or sugary food help. See the side effects guide for more.
When do I increase the dose?: On the schedule your prescriber set, which follows the licensed step-up. For Mounjaro you reach the first full dose (5 mg) at week 5; Wegovy follows a fixed 16-week step-up to 2.4 mg. Use the dose schedule tool to map the dates, and never change the dose yourself.

Sources

From the UK leaflets and NHS pages as of 3 November 2026. The doses are the licensed step-up schedules; follow the one your prescriber set. This is educational reference, not medical advice.