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Why am I not losing weight on Mounjaro?

Robbie Puddick (RNutr)
Written by

Robbie Puddick (RNutr)

Content and SEO Lead

Dr Rachel Hall
Medically reviewed by

Dr Rachel Hall (MBCHB)

Principal Doctor

10 min read
Last updated September 2025
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The reasons why you’re not losing weight on Mounjaro might be that you’re not eating in a calorie deficit, you’ve hit a temporary weight-loss plateau, or the current dose that you’re on isn’t high enough to lower your hunger to the point where you’re eating less.

Important safety information: Mounjaro (tirzepatide) is a prescription medication approved by the MHRA for treating type 2 diabetes and obesity. This article provides general information and shouldn’t be used as a substitute for medical advice. Always consult with your healthcare provider before making any changes to your medication or treatment plan.

Not everyone responds the same way to Mounjaro (tirzepatide), and other factors may also contribute to a weight-loss plateau, such as other medications or health conditions impacting our ability to lose weight.

It’s also important to note that the clinical trials1 of Mounjaro were conducted with participants undergoing lifestyle changes, specifically improving their nutrition, exercise, and sleep habits.

To maximise your weight-loss results and improve your health, it’s important to focus on creating new healthy habits while taking Mounjaro. To the extent that we’d say there’s no point taking Mounjaro unless you also change your habits.

Common issues What’s happening Solution
No calorie deficit Despite reduced hunger, still consuming too many calories Focus on whole foods rich in protein, fibre, fat, and complex carbohydrates and reduce ultra-processed foods
Weight-loss plateau Body has adapted to weight loss, metabolism slowed Patience, consistency, possible activity increase, ensure adequate protein
Dose too low Current dose not sufficient to lower hunger enough to support weight loss Complete titration schedule, wait 4-5 weeks for steady state
Medication interactions Other medications interfering with Wegovy’s effects Consult healthcare provider about medication timing or adjustments
Unrealistic expectations Expecting faster results than medication can provide Understand realistic timeline and recommended weight loss rate of 1-2lbs per week

Medication-assisted weight loss with a future focus

Start with Wegovy or Mounjaro, transition to habit-based health with our support

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How Mounjaro affects weight loss

Mounjaro (tirzepatide) works differently from earlier weight loss medications by mimicking two hormones instead of one. It’s a dual GIP/GLP-1 receptor agonist that:

  • Slows down stomach emptying so you feel fuller longer
  • Reduces hunger signals in the brain’s appetite control centre
  • Decreases food cravings, particularly for high-calorie foods
  • Improves insulin sensitivity, which can help reduce fat storage

According to research published in the New England Journal of Medicine2, Mounjaro has been shown to produce average weight losses of 15-25% of starting body weight over 72 weeks when combined with lifestyle changes.

However, individual responses vary significantly. While some people experience dramatic results, others may see more modest benefits or hit plateaus along the way.

So, let’s analyse the 3 main reasons you might not be losing weight while on Mounjaro.

1) You’re not eating in a calorie deficit

The evidence is clear: we must eat within a calorie deficit to lose excess body fat. When we eat below our energy balance, our body has to find the energy required to fuel our body’s primary functions by burning excess fat.

Mounjaro works by interacting with the brain’s appetite control centre, the hypothalamus, to lower hunger and food-seeking behaviours.

Research5 suggests that Mounjaro can reduce our energy intake by around 31% compared to individuals not taking Mounjaro.

However, we eat for more reasons than physical hunger, and some people might continue to eat enough food that prevents them from achieving a calorie deficit due to psychological, environmental, or habitual reasons.

Additionally, suppose our baseline diet was rich in ultra-processed foods and refined sugars, and we continue to eat this way whilst on Mounjaro. In that case, we may still eat more calories than we need to lose weight.

So, we must transition to a diet based on whole foods to maximise the results of Mounjaro.

Key points:

  • We need to eat in a calorie deficit to lose weight
  • If our baseline diet is rich in ultra-processed foods and we continue to eat this way on Mounjaro, we may still consume more calories than we need to lose weight
  • It’s essential to eat a diet based on whole foods to support sustainable weight loss

2) You’ve hit a temporary weight-loss plateau

Suppose we’ve lost some weight on Mounjaro, but then we hit a plateau, and we can’t budge the scales any more. In this case, we’re likely in a weight-loss plateau.

Weight-loss plateaus are extremely common, normal, and a necessary part of the weight-loss process. Being on Mounjaro doesn’t prevent us from experiencing weight-loss plateaus.

Graph showing typical weight loss progress with plateaus

We have a full guide explaining weight-loss plateaus. However, as a quick summary:

  • Our brain receives signals from many hormones, letting it know how much energy we’re eating and how much fat we have stored. We call this the brain’s ‘set point’.
  • Weight-loss plateaus occur when our brain senses that we’re consuming fewer calories than normal and our fat stores are decreasing it ‘slows down’ our metabolism
  • Evolutionarily, we’re wired to protect fat to ensure survival
  • So, weight-loss plateaus are a survival mechanism in the brain to try and protect us from starvation
  • Fortunately, we can gradually lower our brain’s set point by continuing to lead a healthy lifestyle and being consistent in our habits

Key points:

  • Weight-loss plateaus are a necessary and normal part of the weight-loss process. Mounjaro doesn’t prevent weight-loss plateaus from occurring.
  • Weight-loss plateaus occur when our brain senses we’re losing fat and eating less, so it slows down our metabolism to protect our remaining fat stores
  • We can overcome weight-loss plateaus by being consistent with our healthy habits

3) Your current dose isn’t high enough to promote lower hunger

Mounjaro reduces appetite and hunger, helping you eat fewer calories; this effect is almost immediate when you start Mounjaro.

However, you might notice the effect of lower hunger wearing off after 4-5 days post-injection in the first month of taking Mounjaro.

It can take 4-5 weeks for Mounjaro to reach a level in the body we call a steady state. A steady state is when the drug’s levels in the body remain consistent rather than spiking and falling.

Interestingly, this initial weight loss is no different to other weight loss treatments or the impact of diet interventions on weight loss. The real effect of Mounjaro is seen beyond three months.

Mounjaro is a long-acting medication that’s started at a lower dose to reduce the number and severity of side effects as it’s built up to a higher maintenance dose.

Additionally, we might find that our body adapts to the lower doses, and hunger can increase. However, we might find this reversed when we increase the dose.

Key points:

  • The lower doses of Mounjaro can wear off after 4-5 days
  • It can take up to 4-5 weeks for the medication to reach a ‘steady state’ where its levels are consistent in the blood
  • Weight loss may be steady at the beginning but become more consistent as you increase your dose

Timeline expectations: What to expect when on Mounjaro

Understanding the typical timeline of Mounjaro’s effects can help you set realistic expectations and recognise when something might be off track.

Still, everyone’s experience with weight-loss medications will be different and may not mirror the timeline below.

Timeframe What to expect Common challenges
First 2 weeks Rapid reduction in hunger, possible initial side effects, modest weight loss of 1-2kg Nausea, feeling full, and learning to adjust portion sizes
Weeks 3-8 More consistent lower hunger, steadier weight loss (0.5-1kg per week), and adaptation to side effects Hunger may return before the next dose at lower doses, and emotional eating habits may persist
Months 3-4 Steady weight loss continues, first potential plateau, side effects usually ease First major plateau, need to address environmental and emotional eating triggers
Months 5-6 Continued weight loss, habit formation becomes crucial Potential adaptation to medication effects, need for lifestyle consistency
Months 7-12 Slower but continued progress, focus on maintenance strategies Second major plateau, requires consistency of healthy habits

 

Not a magic pill

Weight-loss injections are most effective when combined with a healthier lifestyle. They can help kickstart weight loss while you commit to developing healthier habits.

Mounjaro and other weight loss injections, like Ozempic and Wegovy, can allow you to make lifestyle changes to support long-term weight loss.

These medications can help silence food-related thoughts and give you a boost of confidence with more immediate weight-loss results.

They can also buy you the time and headspace to understand why your body may have struggled to lose weight and build new long-term healthy habits.

The core focus of our medication programmes is to calm down the feeling of food noise, lower your cravings, and allow you to build healthier habits to keep the weight off for good.

The ultimate goal is to make losing weight feel second nature.

Frequently asked questions

How long does it take to see weight loss results on Mounjaro?

Most people begin to notice weight loss within the first 2-4 weeks on Mounjaro, though initial results may be modest.

The most significant results typically appear after 3-6 months of consistent use, once you’ve reached higher maintenance doses.

According to clinical trials, patients lost an average of 15-20% of their starting weight over 72 weeks. Individual results vary significantly based on starting weight, dosage, and lifestyle factors.

Can you build tolerance to Mounjaro?

Some patients report experiencing tachyphylaxis (decreased response) to Mounjaro over time, particularly at lower doses. This doesn’t necessarily mean the medication has stopped working completely.

Research suggests that increasing to the next dose (up to the maximum 15mg) can often restore effectiveness.

If you’ve been on the maximum dose for several months and notice diminishing effects, consult your healthcare provider to discuss potential solutions, including habit changes that can enhance the medication’s effects.

What should I eat while taking Mounjaro to maximise weight loss?

Focus on a diet rich in protein (25-30% of calories), high-fibre vegetables, and healthy fats while limiting ultra-processed foods and refined carbohydrates.

Protein is particularly important on Mounjaro as it helps preserve muscle mass during weight loss and further increases satiety.

Aim for a portion of protein the size of an open hand with each meal. Many people find smaller, more frequent meals easier to manage on Mounjaro due to the feeling of fullness.

Stay well-hydrated and consider working with a dietitian to create a personalised nutrition plan that works with Mounjaro’s effects.

Should I exercise while on Mounjaro?

Yes, regular exercise is highly recommended while taking Mounjaro. Physical activity, particularly strength training, helps preserve muscle mass during weight loss and improves insulin sensitivity.

Start with light activities, such as walking, and gradually increase the intensity as your body adapts. Aim for 150 minutes of moderate activity weekly and include 2-3 strength training sessions.

Some people report having less energy for intense workouts on Mounjaro, especially initially. Listen to your body and adjust accordingly.

The combination of Mounjaro and regular exercise leads to better body composition outcomes than medication alone.

What happens if I stop taking Mounjaro?

If you stop taking Mounjaro, you’ll likely experience a gradual return of hunger and appetite within 2-4 weeks as the medication clears from your system.

Without proper habit formation, most people regain approximately two-thirds of their lost weight within one year of stopping GLP-1 medications.

However, research shows that those who develop sustainable eating, exercise, and lifestyle habits while on the medication maintain significantly more of their weight loss.

Take home message

If you’re not losing weight on Mounjaro, it’s most likely due to one of three factors: not achieving a calorie deficit despite reduced hunger, experiencing a normal weight-loss plateau, or needing a higher dose to manage your appetite effectively.

Remember that Mounjaro is an effective medication, but it works best when combined with sustainable lifestyle changes.

The most successful patients use the medication as an opportunity to develop healthy habits that will support long-term weight management.

Based on our research, those who combine Mounjaro with comprehensive lifestyle support can achieve significantly better results and maintain more of their progress after stopping the medication.

If you’re struggling with your weight loss journey on Mounjaro, consider getting support to help you build and maintain healthy habits in the long term.

Second Nature's Mounjaro and Wegovy programmes

Second Nature provides Mounjaro or Wegovy as part of our Mounjaro and Wegovy weight-loss programmes.

Why choose Second Nature over other medication providers, assuming you're eligible?

Because peace of mind matters.

We've had the privilege of working with the NHS for over eight years, helping people across the UK take meaningful steps toward a healthier, happier life.

Our programmes are designed to meet people where they are, whether that means support with weight loss through compassionate one-to-one health coaching, or access to the latest weight-loss medications (like Mounjaro and Wegovy) delivered alongside expert care from a multidisciplinary team of doctors, psychologists, dietitians, and personal trainers.

At the heart of everything we do is a simple belief: real, lasting change comes from building better habits, not relying on quick fixes. We're here to support that change every step of the way.

With over a decade of experience, thousands of lives changed, and a long-standing record of delivering programmes used by the NHS, we believe we're the UK's most trusted weight-loss programme.

We hope to offer you something invaluable: peace of mind, and the support you need to take that first step.

References

  1. Jastreboff AM, et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine, 387(3), 205-216.
  2. Richards R, et al. (2025). A Remotely Delivered, Semaglutide-Supported Weight Management Program: 12-Month Outcomes From a Retrospective Service Evaluation. JMIR Formative Research, 9(1), e72577.
  3. Wilding JP, et al. (2022). Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes, Obesity and Metabolism, 24(8), 1553-1564.
  4. National Institute for Health and Care Excellence. (2023). Tirzepatide for treating type 2 diabetes (TA924)
  5. Heise T, et al. (2023). Tirzepatide Reduces Appetite, Energy Intake, and Fat Mass in People With Type 2 Diabetes. Diabetes Care, 46(5), 998-1004.

Medication-assisted weight loss with a future focus

Start with Wegovy or Mounjaro, transition to habit-based health with our support

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Write a response

Nicole P Best

21 February, 2025

I’ve been on Mounjaro for 1 year and have hit a weight-loss plateau for over the last 3 months. I’ll try to get in a stricter calorie deficit, strict gym regimen with intense cardio, and restrictive weight training and lower my carb intake. I’m at the highest Mounjaro 15 mg and I’m worried that my body is rejecting the medication it has lowered my fasting and A1C blood sugar numbers tremendously. My only real side effects were minor sulfur burps and bad constipation which I was ok using every laxative method possible I will endure that for weight loss any day. Mounjaro also allowed me to feel better about myself and outlook on life.


Simon

18 January, 2025

Hi I have been on Mounjaro since October 24 and have lost 3stone but over the last couple of weeks I have had bad burping and diarrhoea any suggestions which may help me.


Holly

13 December, 2024

I have been on Mojarro for over a month. I lost 10 pounds but still is moving a little slow for me. My metabolism slow most of the time I don’t know what to eat.


Sunny Lynn

1 May, 2024

I’m not losing weight on Mounjaro and I was wondering if Ozempic would work better for me?


Mike Gibbs

7 May, 2024

Hi Lynn – if you’re in the UK then unfortunately Ozempic is not available for weight loss. Wegovy is available for weight loss, and uses the same underlying drug (semaglutide).

It would be very difficult for us to say whether Wegovy would work better for you, without knowing your medical history and experience with Mounjaro. It may be the case that Mounjaro is having an effect but you might need to make some further adjustments to your lifestyle habits to push through any weight-loss plateau that you’re experiencing. Also, occasional weight-loss plateaus are expected during a weight-loss process; it’s very rarely a linear journey.


Kyle

21 July, 2024

Yes it is available for weight loss in the UK. Providing you meet certain criteria. It’s available from all major pharmacies including Boots, Asda, Superdrug even sell it and a plethora of online chemists.

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