Starting Mounjaro: What to Expect in the First Month

The first month is where most people either settle into treatment or talk themselves out of it — usually because nobody told them what was normal. This is what actually happens.

It forms part of our complete guide to Mounjaro (tirzepatide).

You start on a dose designed to be tolerated, not to work

Treatment begins at 2.5 mg once a week for four weeks. This is a starting dose, and its job is to let your gut get used to the medicine. It is not the dose at which most of the effect is expected.

That matters because it sets expectations correctly. People who expect dramatic change in month one are often disappointed, conclude it is not working, and stop — when in fact they have not yet reached a treatment dose. Provided it is tolerated, the dose steps up to 5 mg after four weeks, and can rise in 2.5 mg increments at least four weeks apart from there.

Equally, some appetite change in the first weeks is common. Both experiences are normal.

Week by week

The injection itself

• Once a week, same day each week. Pick a day you will remember and set a reminder.
• Any time of day, with or without food.
• Into the abdomen, thigh or upper arm, under the skin — not into muscle.
• Rotate the site each week to reduce lumps and irritation.
• Store it in the fridge. Follow the leaflet on temperature and on how long it can be out.
• If you miss a dose, the leaflet explains the rules on how late is too late. Check it rather than guessing, and ask us if it is unclear.

We will show you how to use the device at your appointment and watch you do it, rather than handing it over with a leaflet.

Eating in the first month

Your stomach is emptying more slowly, so how you eat matters more than it used to.

• Smaller portions, eaten slowly. The single most useful change.
• Stop when full. Finishing the plate out of habit is the commonest cause of nausea.
• Protein first. Appetite drops, so it becomes easy to under-eat protein, which matters for preserving muscle while losing weight.
• Fluids throughout the day. Thirst signals get muddled, and dehydration drives both nausea and constipation.
• Go steady on rich, fatty and fried food, which sits longest.
• Alcohol is often less well tolerated, and irritates the stomach.

The mistakes we see most

• Expecting the starting dose to be the treatment dose — and quitting at week three.
• Eating too little. Appetite suppression makes it easy to drop well below what your body needs, which causes fatigue, hair thinning and muscle loss.
• Pushing through significant nausea instead of asking whether to hold the dose.
• Forgetting the contraception window — extra precautions are advised for four weeks after starting and after each dose increase. → Mounjaro and contraception
• Dropping exercise. The medicine is licensed alongside diet and activity, and resistance work protects muscle.
• Not weighing at all, or weighing daily. Once a week, same day, same conditions.

Your four-week review

At the end of the first month we look at how you have tolerated it, what has changed, your weight and blood pressure, whether any side effects need managing, and whether it is appropriate to increase the dose or stay put for longer. Staying at the starting dose for another month is a perfectly reasonable outcome.

→ Starting dose vs maintenance dose explained

Where to start in Hampshire

We will show you how to use the device in person and see you again at four weeks. Weight management appointments run at all four branches, serving Havant, Emsworth, Rowlands Castle, Waterlooville, Bedhampton, Leigh Park, Portsmouth, Fareham, Petersfield and Chichester.

• Bosmere Pharmacy, Solent Road, Havant PO9 1DQ — 023 9248 1721 · open 7 days, until 9pm Mon–Sat
• Davies Pharmacy, 12 West Street, Havant PO9 1PF — 023 9248 3146
• Emsworth Pharmacy, West Street, Emsworth PO10 7DU — 01243 968 869
• Rowlands Castle Pharmacy, 14 The Green, Rowlands Castle PO9 6BN — 023 9241 3952

Read more

• Mounjaro (tirzepatide): the complete patient guide
• Am I eligible? BMI and criteria explained
• Side effects: what’s common and what needs urgent attention
• Mounjaro and contraception

Frequently asked questions

What dose do you start on?
2.5 mg once weekly for four weeks. It is a starting dose for tolerance rather than a treatment dose.

When will I notice something?
Many people notice appetite changes within the first couple of weeks, but the starting dose is not where most of the effect is expected.

How bad is the nausea?
Very variable. Often worst in the days after the first injection and after each increase, and it usually eases. Smaller, slower meals help most.

Where do I inject?
Abdomen, thigh or upper arm, under the skin, rotating sites weekly.

What if I miss my weekly dose?
The leaflet sets out the timing rules. Check it rather than guessing, and contact us if unclear.

Can I drink alcohol?
It is often less well tolerated, irritates the stomach and adds calories. Worth minimising, particularly early on.

Do I still need to diet and exercise?
Yes. The medicine is licensed as an adjunct to a reduced-calorie diet and increased physical activity.

General information reflecting the UK licensed use of tirzepatide. Not personalised medical advice and not a substitute for the patient information leaflet supplied with your medicine.