Jump to: Timeline of weight loss | Factors affecting your results | How to maximise weight loss | When to be concerned | Mounjaro vs other treatments | Frequently asked questions | Take home message
According to randomised controlled trials, you start losing weight immediately after taking Mounjaro, with most people losing around 4% of their body weight after one month1.
Mounjaro (tirzepatide) reduces appetite and hunger, helping you eat fewer calories; this effect is almost immediate.
However, you might notice the impact of lower hunger wearing off after 4-5 days post-injection in the first month of taking Mounjaro.
It can take around four 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.
Important safety information: Mounjaro (tirzepatide) is a prescription-only medication for treating type 2 diabetes and managing obesity. This article is for information purposes only. Always consult with your healthcare provider before starting any new medication, particularly if you have had your gallbladder removed or have other health conditions.
UK prescribing guidelines
The National Institute for Health and Care Excellence (NICE) approved Mounjaro (tirzepatide) for weight management in adults with obesity in March 20246. According to NICE guidance, Mounjaro is recommended for people with:
- BMI of at least 35 kg/m² and at least one weight-related health condition, or
- BMI of at least 30 kg/m² with type 2 diabetes
NICE recommends Mounjaro be prescribed alongside a reduced-calorie diet and increased physical activity, with treatment reviewed after 12 months to assess effectiveness6.
Timeline of weight loss on Mounjaro
First month expectations
Clinical trial data shows that participants typically lose around 4% of their starting body weight in the first month on Mounjaro1. For someone weighing 100kg, this translates to approximately 4kg.
During this initial period, you’ll start on the lowest dose (2.5 mg) to help your body adjust to the drug.
The hunger-lowering effect begins working almost immediately, though you might notice hunger returning 4-5 days after each injection as your body adapts.
NICE guidance states that people should be assessed for a response to treatment after 6 months, with an expectation of at least 5% weight loss to continue treatment6. Research shows most people exceed this threshold within the first three months.
Months 2-3: The acceleration phase
By the end of month two, average weight loss increases to around 6% of starting body weight1. This is when many people transition to higher doses (5 mg or 7.5 mg), and the steady-state concentration means more consistent appetite control throughout the week.
Month three often marks a turning point where the medication’s full effects become apparent, with some studies showing weight loss reaching 8-10% of starting body weight2.
Months 4-6: Steady progress
During this period, most people reach their maintenance dose (10 mg, 12.5 mg, or 15 mg). Weight loss continues steadily, with clinical trials showing average losses of 15-16% by month six2.
This phase is characterised by more predictable, consistent weight loss as your body fully adapts to the medication and you’ve established new eating patterns. By this point, you’ll have exceeded the NICE criteria for continuing treatment.
Beyond 6 months
Long-term data from the SURMOUNT trials show continued weight loss up to 72 weeks, with average total weight loss reaching 20.9% on the highest dose (15 mg)3. However, the rate of loss typically slows after the first six months.
Some people continue losing weight throughout the first year, while others transition to weight maintenance after 8-10 months. NICE recommends reviewing treatment at 12 months to ensure continued effectiveness6.
Factors affecting your rate of weight loss
Not everyone loses weight at the same rate on Mounjaro. Several factors influence individual results:
| Factor |
Impact on weight loss |
Why it matters |
| Starting BMI |
Higher BMI often = faster initial loss |
People with more weight to lose typically see larger absolute numbers |
| Dose level |
Higher doses = greater average loss |
15 mg dose shows ~5% more weight loss than 5 mg3 |
| Adherence |
Consistent use = better results |
Missing doses can slow progress |
| Lifestyle changes |
Diet + exercise = enhanced results |
NICE guidance requires lifestyle changes alongside medication6 |
| Other medications |
Some drugs may slow loss |
Certain antidepressants and steroids can affect results |
| Medical conditions |
Can impact rate |
PCOS and thyroid issues may influence response |
Individual variation is normal
While clinical trials provide averages, individual experiences vary significantly. Some people lose weight quickly in the first month, while others take longer to respond. Both patterns can lead to successful long-term results.
The SURMOUNT-1 trial showed that while the average weight loss was 20.9%, individual results ranged from minimal loss to over 30% of body weight3.
How to maximise weight loss on Mounjaro
Dietary strategies
To maximise weight loss on Mounjaro, focus on:
Protein intake: Aim for 25-30% of your daily calories from protein to preserve muscle mass during weight loss. This means roughly 30-40g of protein per meal (a portion the size of an open hand).
Whole foods: Build meals around vegetables, lean proteins, fat, and complex carbohydrates rich in fibre. These foods nourish our bodies, while Mounjaro helps to control hunger.
Meal timing: Eating 3 balanced meals a day helps to stabilise blood sugar and maximise the medication’s effects. You can include protein-rich snacks bewtween meals if you need to.
Hydration: Adequate water intake is crucial, especially if experiencing common side effects like nausea or constipation.
Exercise considerations
Physical activity enhances Mounjaro’s effects and is a requirement of NICE prescribing guidelines6:
Start gradually: If new to exercise, begin with 10-15 minute walks and build slowly. Aim to do an exercise you enjoy.
Resistance training: Include strength exercises 2-3 times weekly to preserve muscle mass. This doesn’t have to include heavy weights; body weight exercises like calf raises, squats, and push ups are just as effective.
Consistency over intensity: Regular moderate activity is more beneficial than sporadic intense sessions.
Managing side effects for optimal results
Common side effects can impact weight loss if not managed properly:
Nausea management: Eat smaller portions, limit ultra-processed foods, and consider ginger tea. Speak to your provider if nausea stops you from eating altogether.
Constipation: Increase fibre gradually, eat only cooked foods, stay hydrated, and maintain physical activity. Consider a magnesium supplement if needed.
Fatigue: The most common cause of fatigue during weight loss is not eating enough. Avoid a very-low-calorie diet and aim to continue eating 3 main meals a day, with protein-rich snacks in between meals if needed.
When to be concerned about your rate of weight loss
Too fast
Losing more than 2lbs of body weight per week consistently may indicate:
- You’re not eating enough
- Eating too little protein
- May need to reduce the dose
Rapid weight loss can increase the risk of gallstones and muscle loss. Contact your prescriber if you regularly lose more than 2lb per week.
Too slow
If you’re losing less than 0.5% body weight per week after the first month, consider:
- Whether you’ve reached an adequate dose
- Reviewing your dietary habits
- Checking for medication interactions
- Discussing with your prescriber about what dose is right for you
Remember that NICE requires at least 5% weight loss by 6 months to continue treatment6. If you’re not on track to meet this target, discuss options with your healthcare provider.
Mounjaro vs other weight loss treatments
Understanding how Mounjaro compares to other options helps set realistic expectations:
| Treatment |
Average weight loss |
Timeline |
Key differences |
| Mounjaro (tirzepatide) |
20.9% at 72 weeks3 |
Steady over 12-18 months |
Dual hormone action (GIP/GLP-1) |
| Wegovy (semaglutide) |
14.9% at 68 weeks4 |
Similar pattern, slightly less |
Single hormone (GLP-1) only |
| Saxenda (liraglutide) |
8% at 56 weeks5 |
Plateaus earlier |
Daily injection required |
| Orlistat |
5-7% at 12 months |
Gradual |
Works differently (fat absorption) |
| Diet and lifestyle alone |
3-5% at 12 months |
Variable |
High regain rate |
Mounjaro typically produces faster initial weight loss than other GLP-1 medications, particularly in the first 3-6 months.
Frequently asked questions
How much weight will I lose in the first week on Mounjaro?
Most people lose 0.5-1kg in the first week, though this can vary. Initial weight loss often includes water weight as your eating patterns change. The appetite suppression begins immediately, but significant fat loss takes time.
Why am I not losing weight on Mounjaro after 2 weeks?
Two weeks is too early to assess effectiveness. It takes 4-5 weeks to reach steady state, and some people don’t see significant weight loss until reaching higher doses. Ensure you’re following injection instructions correctly and give it time.
Can I lose too much weight too quickly on Mounjaro?
Yes, losing more than 2lbs per week consistently can increase the risk of gallstones and muscle loss.
If you’re losing weight very rapidly, discuss with your prescriber about adjusting your dose or dietary intake.
Does everyone lose weight on Mounjaro?
While most people lose weight on Mounjaro, studies show about 5-10% of participants are ‘non-responders’ who lose less than 5% body weight3.
Dose optimisation and lifestyle factors can help improve response. NICE requires at least 5% weight loss by 6 months to continue treatment6.
How long does Mounjaro take to work for weight loss?
Appetite suppression begins immediately, but meaningful weight loss typically starts within 4 weeks. Most people see significant results by 12 weeks, with continued loss for 12-18 months.
Will I plateau on Mounjaro?
Weight loss naturally slows over time, but true plateaus (no loss for 4+ weeks) are less common on Mounjaro than with diet alone. If you plateau, your prescriber may adjust your dose or recommend lifestyle modifications.
What happens to weight loss when I stop Mounjaro?
Studies show people typically regain weight after stopping, though the amount varies. Maintaining healthy habits developed during treatment helps minimise regain. Some people transition to lower doses for maintenance.
Is weight loss on Mounjaro permanent?
Weight loss is maintained as long as you continue the medication and healthy habits. Like all obesity treatments, stopping Mounjaro without maintaining lifestyle changes typically results in weight regain.
Am I eligible for Mounjaro on the NHS?
According to NICE guidelines, you may be eligible for Mounjaro on the NHS if you have a BMI of at least 35 kg/m² with a weight-related health condition, or a BMI of at least 30 kg/m² with type 2 diabetes6.
However, NHS availability varies by region and local commissioning decisions.
Take home message
Mounjaro produces significant weight loss for most people, with typical results of 4% body weight loss in the first month, increasing to 15-20% over 12-18 months.
Individual results vary based on dose, starting weight, and lifestyle factors.
The medication works immediately to reduce appetite, but reaching optimal weight loss takes time and patience.
The best results are achieved by combining Mounjaro with sustainable dietary changes and regular physical activity, as recommended by NICE guidelines.
Remember that Mounjaro is a tool to support weight loss while you develop healthier habits. The skills you build during treatment – like portion awareness, regular meal timing, and consistent exercise – are what enable weight maintenance 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
- Frías JP, Davies MJ, Rosenstock J, et al. (2021). Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes. New England Journal of Medicine, 385(6), 503-515.
- Rosenstock J, Wysham C, Frías JP, et al. (2021). Efficacy and safety of a novel dual GIP and GLP-1 receptor agonist tirzepatide in patients with type 2 diabetes (SURPASS-1). The Lancet, 398(10295), 143-155.
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine, 387(3), 205-216.
- Wilding JPH, Batterham RL, Calanna S, et al. (2021). Once-Weekly Semaglutide in Adults with Overweight or Obesity. New England Journal of Medicine, 384(11), 989-1002.
- Pi-Sunyer X, Astrup A, Fujioka K, et al. (2015). A Randomized, Controlled Trial of 3.0 mg of Liraglutide in Weight Management. New England Journal of Medicine, 373(1), 11-22.
- National Institute for Health and Care Excellence. (2024). Tirzepatide for managing overweight and obesity (TA1026).
