Mounjaro Weight Loss Week by Week

You’ll always start on 2.5mg of tirzepatide regardless of whether you’ve tried Mounjaro in the past or have taken other weight loss injections. For example, you can’t switch from a high dose of Wegovy to a high dose of Mounjaro as the active ingredients are different and you may react differently. You can find out more information in our guide on switching from Wegovy to Mounjaro.

Before injecting Mounjaro for the first time, choose a day and time that will work best for you every week going forward. Mounjaro works best when injected at the same time each week because:

1. The medication can stay at a steady level in your bloodstream and will continue working at its best. This means the right level of medication will be in your system throughout your treatment.
2. Your body will adjust to the medication schedule as time goes on, so taking it at the same time every week can help your body adjust better, possibly reducing side effects.

What to expect in week 1 on Mounjaro

Weight loss: In week 1 on Mounjaro, you might see a sudden weight drop, some weight loss, or very little weight loss. One study found that in the first 4 weeks, participants lost just less than 1% of their starting weight per week.

If you see a sudden weight drop, this could be ‘water weight’ or fluid loss. This happens within the first week of eating fewer calories because your body releases stored carbohydrates (called glycogen) to make up for the ‘lost’ energy it’s no longer receiving. Each gram of glycogen is stored with at least 3g of water. If you have adjusted your lifestyle alongside taking Mounjaro, for example, if you’ve drastically changed how you eat, how much you eat and how much you exercise, you may see results fast.

Once your glycogen stores are empty, your body will metabolise excess fat for energy, so you’re more likely to see fat loss after week 1.

Side effects: Very common side effects like nausea, diarrhoea, vomiting or constipation are most likely during the first week. These are usually mild and should reduce as you adjust to the medication, but they can come back with a dose increase.

You can stay on a lower dose long-term if you need to, as long as you’re still losing weight. Our Mounjaro dosage guide talks about how to move through the doses and what to do if you want to stay on a lower dose in more detail.

Reduced appetite: You might notice Mounjaro starting to work to reduce your appetite, but how the first dose works for you is individual. You may already find you don’t feel as hungry, or you may need more time on the medication or a higher dose to really feel the effects. Mounjaro can be increased up to 15mg a week, so 2.5mg is still a very low dose.

Week 1 tips

Side effects are most likely in week 1, so make sure you’re eating enough and choosing balanced, healthy options to keep up your nutrition and strength.

If you are worried about getting side effects, see if there’s a time of day that might be better to take it. For example, if it makes you feel nauseous it might be better to inject Mounjaro in the evening after you’ve eaten a filling meal. If you find your chosen time and day don’t work, you can change when you take Mounjaro as long as you don’t do this often.

You can find more information on switching days in the patient information leaflet.

Focus on how to set yourself up for effective weight loss by starting a weight loss and exercise plan for the following weeks or months of treatment. Finding meal plan ideas or a Mounjaro diet guide can help get you on the right track.

Make sure to stay hydrated, especially if you get side effects. Dehydration can make side effects worse. Keep drinking water (6 to 8 glasses a day) even if you cannot eat much in the first few days.

Mounjaro week 2 is likely to be similar to week 1. The dosage schedule remains the same, so you’ll continue on 2.5mg until week 5. With a second dose in your system, you might start to feel the effects of Mounjaro more as you continue following your diet plan.

In terms of side effects, they may stay the same or start to get better as your body adjusts to the medication. If they become severe and unmanageable, speak to your doctor for advice.

Weight loss in week 2 can vary from ‘a little’ to ‘some’ depending on your body, age, metabolism, and your diet and exercise regime. Studies show people usually lose less than 1% of their weight each week in the first 4 weeks, which is around 1kg or 2.2 pounds per week.

Weeks 3 and 4 are where most people notice their side effects getting better or going away. You’ll continue taking 2.5mg, but your body should have started getting used to the treatment now.

By week 4 of taking Mounjaro, study participants lost under 4% of their starting weight, but this isn’t to say you won’t lose more. It depends on how well you’re following a reduced-calorie diet and exercising, and how the medication works for you.

The effects of the tirzepatide in Mounjaro should become more apparent now it’s had time to reach a steady level in your bloodstream. You may notice you feel fuller for longer and don’t feel as hungry between meals.

You should still eat, even if you don’t feel hungry, or you may put yourself at risk of a nutritional deficiency. Losing weight by not eating isn’t sustainable and has been proven to cause weight gain in the future.

Week 5 is your first dose increase. You’ll start taking 5mg of tirzepatide each week from now, for at least 4 weeks. If you want to continue moving through the dosage schedule, you’ll take 5mg from weeks 5 to 8 before the next increase on week 9.

Weight loss: In studies, people lost on average 5% to 6% of their body weight by this point. You may start to notice consistent weekly weight loss, but remember it’s best to only weigh yourself every 2 to 4 weeks, as your weight can fluctuate from day to day. Counting the number on the scales isn’t the only way to see weight loss either. Check how your clothes fit or your waist measurements, as these can change even when the scales don’t.

Side effects: Because of your dose increase, you might notice some side effects. This is because you’re taking a higher dose now so again your body may need time to readjust. Most side effects will go away within a few days to a few weeks and should be mild, such as nausea, constipation, stomach ache, or diarrhoea.

If you’ve been getting severe or long-lasting side effects, your doctor may encourage you to stay on 2.5mg for a few more weeks to see how you get on. You should reconsider your treatment if side effects continue for a further 4 weeks on the lowest dose, especially if they’re affecting your daily life.

Medication effect: You might notice a bigger change in your appetite and how full you feel after another dose increase, which makes it easier to manage your reduced-calorie diet.

You’ve changed your diet and lifestyle for a whole month now, so you may have more energy or feel healthier overall, especially if you’re getting plenty of exercise and essential nutrients from your diet. Continue with your meal plans and exercise regime and see how you manage your dose increase for the next 4 weeks.

At week 9, you can start taking 7.5mg of tirzepatide each week.

Weight loss: You’re likely to have lost 9% to 12% of your body weight by this point but this could be higher or lower.

Side effects: As with a new dose increase comes the chance of side effects but this is different for every person. If you usually get side effects with each dose increase, adjust your diet and lifestyle accordingly for the next few days, such as:

• eating small, plain meals to help with nausea
• getting over-the-counter medications to help with diarrhoea, constipation, or acid reflux symptoms
• taking it easy and getting plenty of rest while your body adjusts

Remember, if you’re happy with your results on 5mg and don’t want to increase your dose at this point you don’t have to. Speak with your doctor about staying on a lower dose, especially if you have side effects. You can always change your mind later or increase your dose once your side effects have improved.

Medication effect: You might feel more of an effect from a higher dose, such as feeling even less hungry between meals.

On week 13, you can increase to the 10mg weekly dose.

Weight loss: By week 13, you may have lost around 13% of your starting weight according to research. As long as you’re losing weight by this point, the medication and lifestyle changes are working so don’t worry if you’ve lost less than this.

Side effects: A new dose increase can come with a chance of side effects until your body adjusts, so make sure you’re ready to manage them at home if you do get them.

Medication effect: A higher dose should help even more with appetite suppression if the lower doses aren’t fully managing your hunger levels yet. You can still feel some hunger on Mounjaro but it should be easier to reduce your calorie intake, especially compared to not taking it.

If you’re still snacking and eating sugary or high-fat foods, this may be due to habit and cravings rather than hunger. Speak to a doctor or counsellor if you use food to cope with stress or if you’re struggling to break the habit of snacking.

Following the Mounjaro dosage schedule (a 2.5mg dose increase every 4 weeks), you’ll reach the maximum maintenance dose of 15mg on week 21 which you’ll stay on for the rest of your treatment. It may also take longer than 21 weeks if you stay on a lower dose initially.

If you stay on a lower dose for longer than 4 weeks, you can increase it whenever you’re ready.

How much weight can I lose?

Mounjaro is a long-term obesity and overweight treatment and should be used alongside diet and exercise changes that you can continue following to maintain your weight loss in the future. Clinical studies on weight loss with Mounjaro show the best results after taking it for 72 weeks.

The maintenance doses used in the study were 5mg, 10mg and 15mg but you can stay on any dose you’re happy with. By week 72, participants lost:

Here are our best tips for reaching your weight loss goals with the help of Mounjaro.

Reach a 600-calorie deficit – Successful weight loss requires a deficit of around 600 calories per day compared to your recommended daily amount (which is different for men and women). You should be able to reduce your calorie intake on Mounjaro as it makes you feel less hungry and more full, even while eating less. If you’re finding it difficult to reduce your calorie intake, try counting calories using an app and do it slowly, such as cutting out 100 calories per week until you reach 600.

Eat the right foods – Healthy, balanced meals are the best way to lose and maintain weight loss. This means avoiding or limiting foods that are high in fat, calories, sugar, or are highly-processed. Stick to whole foods like fruits, vegetables, lean protein and whole grains. Only have small amounts of healthy fat like seeds, nuts, and olive oil.

Get enough exercise – The NHS recommends exercising every day if you can, even if this is just a short walk to get moving more. Try to reach at least 150 minutes of moderate-intensity exercise or 75 minutes of high-intensity exercise. Don’t do just cardio either, muscle training is a great way to improve your metabolism.

Improve your sleep routine – Poor sleep makes it harder to exercise and eat well, and can lead to cravings and poor food choices due to lack of energy. On the other hand, sleeping well can improve your energy levels, increase your physical activity throughout the day and make weight loss easier. Try improving your sleep routine by getting enough each night (8 hours or so), making your bedroom dark and comfortable for sleep and switching off electronics at least 30 minutes before bed.

Decrease your stress levels – Stress can cause health problems and impact weight loss in many ways, such as contributing to the build-up of stomach fat or making it harder to limit snacking. Try relaxing activities like yoga, meditation or working out, as this can make you feel better and get you out of the ‘fight or flight’ state.

In Mounjaro studies, the best weight loss results were seen after 72 weeks, so you might have not reached the right dose yet, or haven’t given it enough time. We’ve created a ‘why am I not losing weight on Mounjaro’ guide which includes reasons why you may not be losing the weight you expected and what you can do to improve your results.