Mounjaro Weight Loss: Week by Week Results

Mounjaro is the most effective injectable weight loss pen currently available in the UK. It contains the active ingredient tirzepatide, which mimics GLP-1 and GIP hormones in the body.

Mounjaro activates receptors that slow down gastric emptying and promote insulin secretion. This helps with weight loss as it keeps you feeling fuller for longer and regulates food cravings.

Clinical studies have shown that over 72 weeks, you can lose up to 22.5% of your body weight on average when you reach and continue taking the maximum 15mg dose of Mounjaro^[1]. However, week-by-week weight loss on Mounjaro can vary between individuals due to factors like diet, lifestyle, and tolerability to treatment.

This guide explains how much weight you can expect to lose by week and gives advice on getting the best results from Mounjaro.

Mounjaro Weeks 1 to 4

Dose: 2.5mg of tirzepatide

You will begin treatment on a 2.5mg dose of Mounjaro. This helps your digestive system adapt to the medication and is suitable even if you have never taken Mounjaro before.

Average weight loss: Up to 4%

Mounjaro results may differ between you and others in terms of achieved weight loss as this depends on multiple factors such as diet and lifestyle.

On average, you can expect to see up to 4% weight loss in the first four weeks^[1]. It is normal to achieve weight loss results that differ from others taking Mounjaro.

Some patients may experience noticeable weight loss results on Mounjaro within the first month. For others, this may take up to a few months.

It is important to build healthy and consistent habits now to help get the desired weight loss results with Mounjaro. This includes maintaining a balanced and calorie-restricted diet alongside regular exercise.

Recommended reading: What to Eat on Mounjaro: Nutrition Tips and Diet Plan

Mounjaro Weeks 5 to 8

Dose: 5mg of tirzepatide

If you do not experience any severe side effects during weeks 1 to 4, you can be prescribed a 5mg dose of Mounjaro. The new dose will typically be taken for the next four weeks before the next higher dose can be considered.

For more information about dosage schedules, read our in-depth guide: Mounjaro (Tirzepatide) Dosage Guide For Safe and Effective Weight Loss

Average weight loss: Up to 6%

You can begin to notice reduced appetite and initial weight loss during this time period. Clinical trials found that patients lost up to 6% of their body weight on average by this point^[1].

You may also start experiencing mild gastrointestinal side effects such as vomiting or diarrhoea. This is common and is a result of your body adjusting to the increased concentration of the medication.

It is important to stay hydrated throughout treatment, especially if these side effects are experienced. You should contact your treatment provider or doctor if you have any concerns about side effects.

Recommended Reading: Mounjaro Side Effects: What They Are & How To Manage Them

Mounjaro Weeks 9 to 12

Dose: 7.5mg of tirzepatide

You should step up to a higher dose if you are tolerant to the treatment. This helps maintain and accelerate the rate of weight loss as the medication continues to build up in your body.

You need to have stayed on the previous dose for at least four weeks before you step up in dose.

Always follow your treatment provider’s advice regarding dosages and never change doses unless you have been told to do so.

With dose increases, there is a chance that side effects may return or intensify. This is common and usually occurs during a brief period while your body becomes accustomed to the new dose.

Average weight loss: Up to 8%

By week 12, you can lose up to 8% of your body weight on average^[1]. By now, you may be noticing changes to your body weight on a week-to-week basis. This could be how your clothing fits or how you look physically, as well as your body weight on the scales.

On higher doses, the effects of the medication on your appetite regulation and fullness are likely much greater too.

Keep to a consistent treatment schedule and maintain healthy lifestyle changes to make continued weight loss more likely.

Mounjaro Weeks 13 to 20

Dose:

• Weeks 13 to 16: 10mg of tirzepatide
• Weeks 17 to 20: 12.5mg of tirzepatide

After 3 months of consistent treatment, the medication has built up to significant levels in your body.

The effects of the medication on your hunger and appetite should be apparent, and you will very likely experience noticeable changes to your physical appearance and improvements in your overall wellbeing.

Following the dosing schedule, you should increase your dose by a 2.5mg increment on week 17 to 12.5mg if approved by your treatment provider.

Average weight loss: Varies between individuals

At this point in your Mounjaro treatment course, you may start to notice more rapid weight loss as the dosage increases.

Physical changes to your body will likely be easier to spot. You may be noticeably slimmer in the mirror and have dropped a significant amount of body weight.

As before, it is important to keep maintaining the lifestyle changes you have made so far and remain consistent with treatment.

Mounjaro Week 21 and onwards

Dose: 15mg of tirzepatide (maximum dose)

If you have increased your dosage every four weeks, you will reach the maximum dose on week 21. You will then stay on this maximum 15mg dose for the rest of your weight loss treatment.

Research shows that the best results were found after taking Mounjaro for 72 weeks. Despite reaching the maximum dose, it is important to continue taking the treatment to maintain weight loss results.

Average weight loss: Up to 22.5% (over time)

In clinical studies, patients on the maximum 15mg dose lost the greatest amount of body weight over a 72-week period.

You could also lose up to 22.5% of your body weight if treatment is consistently maintained over a similar timeframe^[1]. As before, your lifestyle habits will impact how much weight you can lose.

Getting the best results with Mounjaro

Treatment tips

Weight loss is not immediate on Mounjaro, so it is important to be consistent with the treatment.

The medication needs time to build up in your body before it is most effective. In the first month of taking Mounjaro, you might not notice substantial weight loss results while adjusting to the medication. It is important to continue taking the treatment to ensure the best results.

Follow all of the steps exactly when preparing and administering the pen. This ensures that the correct dose of the medication is delivered and prevents unwanted side effects or injury.

Read more about taking Mounjaro: How to Take Mounjaro® Injections

Before injecting Mounjaro, it is important to check the flow of the pen to ensure the medication is ready to be dispensed from the needle. The flow check process will be explained in detail in the patient information leaflet that comes with the treatment. This step helps prevent any air bubbles from being injected and ensures the right dose is administered.

When injecting, make sure to hold the dose knob long enough to fully deliver the dose. Releasing it too early can lead to medication spilling from the needle once it is taken out.

Refer to the patient information leaflet that is included with the injectable weight loss pen for further instructions.

Lifestyle tips

Avoid skipping meals while taking Mounjaro. This can increase the risk of fatigue, low blood sugar and malnutrition. It can also increase the chances of binge eating.

Maintaining a regular eating routine and following a balanced diet containing fruit, vegetables and lean proteins will help support metabolic health and feelings of fullness.

When paired with consistent physical activity, this allows the body to process food and store energy in a healthy, sustainable manner. This combination of lifestyle changes supports healthy, long-term weight loss.

Taking before and after weight loss images while taking Mounjaro can help you track weight loss. This can also give a sense of progression outside of your body weight on the scales. Being able to physically record your body changing can be motivating, making you more likely to continue treatment consistently.

Frequently asked questions

Can I get Mounjaro on the NHS for weight loss?

Mounjaro is prescribed by the NHS for weight loss. However, there are very specific criteria that patients need to meet to be eligible for treatment through the NHS.

What is the average weight loss on Mounjaro?

The rate of weight loss will change as the concentration of the medication builds up in your body over time.

Long-term, you can lose up to 22.5% of your body weight over 72 weeks when taking the maximum 15mg dose.

How fast can you lose weight on Mounjaro?

The rate of weight loss will vary between individuals. On average, you can expect to lose up to 4% body weight in the first month and up to 8% body weight in the first 3 months of treatment.

How long does Mounjaro take to work?

Mounjaro can work to help reduce body weight within the first month for some individuals. However, this is highly dependent on factors like diet, exercise and tolerability of the treatment.

It could take you a shorter or longer amount of time to notice Mounjaro working compared to others because of these factors.

How much weight can you lose on Mounjaro in a month?

You can expect to lose up to 4% body weight on average in the first month on Mounjaro.

It is normal if you lose more or less weight than this due to lifestyle factors and your response to the treatment.

How much weight can you lose on Mounjaro in 3 months?

If you have been taking Mounjaro for 3 months, you could potentially lose up to 8% body weight on average. By now, you may have stepped up your dose twice, increasing the concentration of the medicine in your body and its effectiveness.

Due to varying lifestyle factors like diet and exercise, you may lose more or less weight compared to others.

Why am I not losing weight on Mounjaro?

Dietary factors are a common cause of not losing weight on Mounjaro. Eating more calories than the body burns can result in weight gain, regardless of treatment. Mounjaro helps to limit appetite, but the medication does not directly cause weight loss by itself.

Also, Mounjaro is a long-term treatment that is more effective at higher doses. You may need to give the medication more time to build up in the body before seeing the results you want.

How long do you stay on Mounjaro for weight loss?

Your treatment provider will determine the exact time frame you will stay on Mounjaro.

Clinical studies show that consistent long-term treatment produces the best results, with patients taking Mounjaro for 72 weeks experiencing up to 22.5% reduction in body weight.

How do you maximise weight loss on Mounjaro?

Regular exercise, eating a balanced and healthy diet, and taking the treatment consistently will help you get the best weight loss results when taking Mounjaro.

Having good sleep is also important to maximise weight loss results. Quality sleep helps the body produce hormones that control appetite, making it easier to consume fewer calories.

Sources

1. Tirzepatide Once Weekly for the Treatment of Obesity, 2022. [Accessed 01/08/2025]