Jump to: How does Mounjaro work? | Signs of losing weight too quickly | Understanding weight fluctuations | Monitoring your progress | When to adjust your approach | Frequently asked questions | Take home message
Losing more than 2 lbs (0.9kg) per week on Mounjaro after the first month is generally considered too quick and may increase the risk of muscle and bone loss while on the medication.
While the medication can lead to significant weight loss initially, research shows the sustainable rate typically settles at 0.5-1kg (1-2 pounds) a week after this period.1
This more moderate rate allows for sustainable fat loss while preserving essential lean tissue.
If you’re experiencing more dramatic losses, this article explains the science behind why slower is often better for long-term success.
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.
What research shows about Mounjaro weight loss rates
Data from randomised controlled trials shows that people taking Mounjaro lose an average of 6% of their body weight in the first eight weeks. This initial rapid loss is normal and includes the reduction in stored carbohydrate (in the form of glycogen) and water.1
The SURMOUNT-1 trial published in the New England Journal of Medicine shows varying weight loss results depending on dosage:1
- 5 mg weekly: Average loss of 16.1kg after 72 weeks
- 10 mg weekly: Average loss of 22.2kg after 72 weeks
- 15 mg weekly: Average loss of 23.6kg after 72 weeks
These figures translate to an initial rate of around 1.6 pounds per week in the first two months, naturally slowing to about 1 pound per week over time. This gradual reduction in weight loss rate is normal and healthy.
| Aspect |
Healthy weight loss |
Losing weight too quickly |
| Rate |
0.5-1kg (1-2 lbs) per week after initial month |
>1kg (>2 lbs) per week consistently after first month |
| Composition |
Primarily fat mass with minimal muscle loss |
Higher proportion of muscle and bone mineral loss5 |
| Energy levels |
Stable or improved |
Fatigue and weakness |
| Hunger |
Moderate, manageable |
Extreme hunger or no appetite |
| Physical signs |
Gradual changes in body measurements |
Hair loss, constant coldness, headaches |
| Long-term sustainability |
Higher success rate |
Higher likelihood of regain and metabolic adaptation |
How does Mounjaro work?
Mounjaro works by mimicking two hormones, GLP-1 and GIP, that communicate with our brain’s appetite control centre.
This dual action helps reduce hunger and food-seeking behaviour, naturally leading to lower calorie intake.1
Some people might be considered ‘hyper-responders’ to the medication and struggle to eat as their hunger levels essentially go down to zero.
In this scenario, it’s very likely that weight loss will occur more rapidly than is recommended for long-term health.
Signs you may be losing weight too quickly on Mounjaro
Look out for these physical indicators that your weight loss rate may be unhealthy:
- Persistent fatigue: Struggling with energy levels throughout the day despite adequate sleep. Your brain requires consistent energy to function optimally, and severe restriction can impact concentration and mood.
- Hair thinning or loss: A noticeable increase in hair shedding affects approximately 5-10% of people during rapid weight loss. This occurs because your body prioritises essential functions over hair growth when resources are limited.
- Feeling unusually cold: This might indicate your metabolism has slowed significantly to conserve energy, a natural response to severe calorie restriction.
- Muscle weakness: Difficulty with normal physical activities you previously found easy, which could indicate loss of muscle mass rather than just fat.5
- Mood changes: Increased irritability, difficulty concentrating, or feelings of depression, which can result from insufficient calorie intake.
The science of metabolic adaptation
When we lose weight rapidly, our bodies undergo a process called metabolic adaptation.
This natural protective mechanism involves reducing energy expenditure (how many calories we burn each day) to prevent excessive weight loss and preserve essential functions.
A study of 101 women published in the Journal of the American Medical Association found that those following a severe calorie restriction lost 1.5 times more lean mass and 2.5 times more bone mineral density than those following a moderate approach.5
In simple terms, the number of calories our body burns each day decreases as the body seeks to maintain fat levels.
Research shows this adaptation can persist even after weight loss stops, making it harder to maintain results long-term.6
Understanding weight fluctuations
Daily weight changes don’t necessarily indicate actual fat loss or gain. Several factors influence these fluctuations:
- Glycogen storage affects water retention – for every gram of carbohydrate stored, your body holds approximately 3-4 grams of water. This explains why reducing carbohydrate intake often leads to rapid initial weight loss.
- Sodium intake influences fluid balance, with higher sodium consumption typically leading to increased water retention. This is why weight often fluctuates after consuming restaurant meals or processed foods.
- Hormonal changes, particularly during the menstrual cycle, can cause weight to fluctuate by 0.5-1.5kg due to water retention. This is normal and doesn’t reflect true fat loss or gain.
Monitoring your progress
Track your weight loss journey using these strategies:
- If you want to weigh yourself, do so at the same time each day, preferably first thing in the morning after using the bathroom. This provides more consistent measurements.
- This doesn’t mean you need to weigh in every day; you should only weigh in as much as you feel is necessary to support your progress
- Take monthly body measurements and log how your clothes are fitting, as the scale doesn’t tell the complete story. Changes in body composition often occur even when weight remains stable.
- Keep a food diary focusing on meal timing and the balance of whole foods rather than calorie counting. This helps ensure you’re eating enough to support healthy weight loss.
- Track non-scale victories like energy levels, how independent you feel, mood, and self-confidence
Nutrition strategies for healthy weight loss
Focus on eating three balanced meals daily, even if your appetite is reduced. Each meal should contain:
- A protein source the size of your palm (25-30% of your plate)
- Complex carbohydrates the size of one closed fist (25% of your plate)
- Vegetables the size of two open hands (50% of your plate)
- A source of fat from whole foods (like olive oil, avocado, or nuts)
- Include 1-2 servings of fruit per day, like berries at breakfast or an apple with lunch
Protein intake is particularly crucial during weight loss. Aim for 1.6-2.2g of protein per kilogram of body weight per day (around 20-40g in each meal) to preserve muscle mass and support metabolic health.8
When to adjust your approach
Contact your healthcare provider if you notice any of these signs:
- Persistent fatigue or weakness
- Difficulty sleeping
- Regular headaches
- Mood changes
- Constant hunger or extremely low appetite
- Consistently losing more than 0.9kg (2 pounds) weekly after the first month4
Your provider may need to adjust your medication dosage or provide additional support.
Focus on developing sustainable habits that support your health beyond weight loss:
- Regular meal patterns that fit your lifestyle
- Eating a diet based on whole foods rich in protein, fat, complex carbohydrates, and fibre
- Enjoyable forms of physical activity
- Stress management techniques
- Consistent sleep routine
- Social support systems
Frequently asked questions
How much weight should I lose per week on Mounjaro?
After the initial month, a healthy weight loss rate on Mounjaro is typically 0.5-1kg (1-2 pounds) per week.1,4 Clinical trials show this more moderate pace helps preserve muscle mass while primarily targeting fat tissue.
Everyone responds differently to the medication, so your results may vary, but consistent losses above this rate should be discussed with your healthcare provider.
Is it normal to lose 10 pounds in the first month of Mounjaro?
Yes, losing 10 pounds (4.5kg) in the first month on Mounjaro is within the normal range.1 Clinical trials show many patients experience more rapid weight loss during the first 4-8 weeks due to water weight and initial metabolic changes. This initial rate typically slows naturally as treatment continues.
What happens if I’m losing weight too quickly on Mounjaro?
If you’re losing weight too quickly on Mounjaro, you may experience fatigue, hair loss, feeling cold, muscle weakness, mood changes, or nutritional deficiencies.5
Rapid weight loss can lead to a loss of muscle and bone density, in addition to fat.
Your healthcare provider might recommend adjusting your dosage, ensuring adequate protein intake, or modifying your eating schedule to slow the rate of loss.
How can I slow down weight loss on Mounjaro if it’s too fast?
To slow down too-rapid weight loss on Mounjaro while still benefiting from the medication:
- Increase your protein intake8
- Add healthy, calorie-dense foods like nuts, seeds, avocados, cheese, and olive oil to meals
- Ensure you’re eating three balanced meals a day, even if not hungry
- Consider adding protein-rich snacks between meals
- Discuss with your healthcare provider about potentially reducing your dosage2,3
Should I reduce my Mounjaro dose if I’m losing weight too quickly?
Never adjust your Mounjaro dose without consulting your healthcare provider.2,3 If you’re losing weight too quickly, schedule an appointment to discuss your concerns.
Your provider might recommend modifying your diet first or adjusting your dose if necessary. They’ll consider your overall health, weight loss goals, and any side effects when making this decision.
Take home message
While Mounjaro can be an effective tool for weight loss, the goal is to lose weight in a way that supports your long-term health and quality of life.
Focus on building sustainable habits, eating a diet based on whole foods, and regular movement rather than rapid results on the scales.
Remember that everyone’s journey is different, and what matters most is finding an approach that works for you while maintaining your health and wellbeing.
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
- Jastreboff, A.M., et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine, 387(3), 205-216.
- National Institute for Health and Care Excellence. (2023). Tirzepatide for treating type 2 diabetes (TA924)
- National Institute for Health and Care Excellence. (2025). Tirzepatide for managing overweight and obesity (TA1026)
- NHS. (2024). Losing weight safely – NHS
- Seimon, R. V., et al. (2019). Effect of Weight Loss via Severe vs Moderate Energy Restriction on Lean Mass and Body Composition Among Postmenopausal Women With Obesity: The TEMPO Diet Randomized Clinical Trial. JAMA Network Open, 2(10), e1913733.
- Fothergill, E., et al. (2016). Persistent metabolic adaptation 6 years after The Biggest Loser competition. Obesity (Silver Spring), 24(8), 1612-1619. doi: 10.1002/oby.21538
- Chaston, T.B., Dixon, J.B., & O’Brien, P.E. (2007). Changes in fat-free mass during significant weight loss: a systematic review. International Journal of Obesity, 31(5), 743-750.
- Leidy, H. J., et al. (2007). Higher protein intake preserves lean mass and satiety with weight loss in pre-obese and obese women. Obesity (Silver Spring), 15(2), 421-429. doi: 10.1038/oby.2007.531.
