Quick Answer: Most patients lose 4% of their body weight within the first month, 8% by month 3, and up to 22.5% of their starting weight by month 18 with Mounjaro. Results vary, but clinical trials show this is the most effective weight loss injection available in the UK.
The Weight Loss Revolution: Mounjaro's Arrival in the UK
The landscape of weight loss treatments has fundamentally changed with the introduction of Mounjaro (tirzepatide) to the UK market. The Medicines and Healthcare products Regulatory Agency (MHRA) authorised Mounjaro via a national application route on 8 November 2023, for weight loss and weight management in adults aged 18 and over.
What makes Mounjaro extraordinary isn't just another weight loss injection – it's the first dual-action medication that targets both GLP-1 and GIP hormone receptors simultaneously.
Happy Pharmacy is proud to offer comprehensive online consultation services for Mounjaro, providing the support and expertise you need throughout your weight loss journey.
Understanding Mounjaro: The Science Behind Rapid Weight Loss
What Makes Mounjaro Different?
Tirzepatide is a once-weekly subcutaneous injectable peptide engineered from the native GIP sequence, with agonist activity at both the GIP and GLP-1 receptors.
The medication works through several mechanisms:
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Appetite Suppression: Signals to your brain that you're full
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Delayed Gastric Emptying: Keeps you full longer
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Improved Insulin Sensitivity: Reduces fat storage
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Enhanced Fat Utilisation: Promotes breakdown of stored fat
Clinical Evidence: What the Trials Show
In SURMOUNT-1, 2,539 overweight/obese adults with complications took varying doses of tirzepatide or placebo over 72 weeks:
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5mg: -16.0% weight
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10mg: -21.4%
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15mg: -22.5%
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Placebo: -2.4%
Timeline: How Quickly Will You See Results?
Week 1–4: The Foundation Phase
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Starting dose: 2.5mg weekly
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Effects:
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Reduced appetite
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Early fullness
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Mild side effects
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Average loss: 4% of starting body weight
Month 2–3: Momentum Builds
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Expected loss: 6% after two months, 9% after three months
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Dose typically increased to 5mg weekly
Month 4–6: Significant Progress
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Expected weight loss: 11% after four months
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Noticeable physical changes and energy improvement
Month 12–18: Maximum Benefits
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15%–22% weight loss after 72 weeks with healthy diet and exercise
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For someone weighing 100kg, this could mean a 15–22kg loss
NHS Approval and Accessibility in the UK
Current NHS Availability
Approved by NICE in December 2024 for specialist obesity treatment. As of 23 June 2025, limited access has begun for:
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Patients with BMI over 40
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Or BMI 35–40 with multiple weight-related conditions
Private Prescription Options
Most people access Mounjaro via private prescription through regulated online providers like Happy Pharmacy, offering:
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Broader eligibility
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Immediate access
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No waiting lists
Safety Profile: Understanding Risks and Benefits
Common Side Effects
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Nausea
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Diarrhoea
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Vomiting
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Constipation
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Decreased appetite
Tips to manage side effects:
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Eat small, frequent meals
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Stay hydrated
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Avoid fatty/spicy foods
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Adjust in 2–4 weeks
Serious Considerations
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Pancreatitis: Seek medical help for severe abdominal pain
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Thyroid concerns: Especially if family history of thyroid cancer
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Kidney function: Dehydration risk from vomiting/diarrhoea
Who Should Not Use Mounjaro
Avoid if you:
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Have/family history of medullary thyroid carcinoma
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Have MEN 2
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Are pregnant or breastfeeding
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Have severe gastroparesis
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Are allergic to tirzepatide
Maximising Your Results: The Complete Approach
Dietary Considerations
Even with reduced appetite, nutrition matters:
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Protein-rich foods – maintain muscle mass
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High-fibre vegetables – digestive health
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Complex carbohydrates – steady energy
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Hydration – crucial for safety and results
Exercise and Physical Activity
Combine with:
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150 minutes of moderate exercise weekly
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2 strength sessions per week
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Daily walking or light movement
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Pick activities you enjoy to stick with it
Monitoring and Support
Happy Pharmacy provides:
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Monthly progress tracking
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Side effect monitoring
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Dose adjustments
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Nutritional support
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Access to licensed UK professionals
Real-World Success Stories and Expectations
Setting Realistic Goals
Every person is different. Weight loss varies depending on:
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Starting weight
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Medication adherence
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Diet and activity levels
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Ongoing support
Long-term Success
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Patients who lose 5% within 12 weeks tend to sustain results
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Most weight loss occurs in the first half of treatment
Success factors:
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Weekly dosing
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Sticking to dietary advice
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Regular movement
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Monitoring progress
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Commitment to long-term change
Getting Started: Your Path to Weight Loss Success
Online Consultation Process with Happy Pharmacy
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Health Assessment: Complete medical questionnaire
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Professional Review: Regulated UK healthcare providers evaluate
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Personalised Plan: Tailored prescription
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Secure Delivery: Discreet, temperature-controlled to your door
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Ongoing Support: Regular check-ins and adjustments
What to Expect in Your First Month
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Week 1: Start 2.5mg and monitor side effects
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Week 2–3: Appetite suppression noticeable
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Week 4: Review and consider dose increase
Monitoring Your Progress
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Weekly: Consistent weigh-ins
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Monthly: Professional reviews
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Quarterly: Full health and goal assessments
Frequently Asked Questions
How long does Mounjaro take to work?
Appetite suppression can begin within days, with weight loss typically visible by weeks 4–6.
Is Mounjaro suitable for everyone?
No. It is intended for:
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BMI 30+
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Or BMI 27–30 with weight-related health conditions
How does Mounjaro compare to bariatric surgery?
While bariatric surgery can be highly effective, Mounjaro offers comparable weight loss without surgery, recovery time, or surgical risk.
The Future of Weight Management
Innovation in Obesity Treatment
Mounjaro is at the forefront of medical weight loss innovation, with ongoing research into even more effective dual-hormone therapies.
Changing Attitudes to Weight Management
Obesity is now recognised as a medical condition, not a personal failing. Mounjaro supports a clinical, regulated approach to weight loss.
Supporting Long-term Success
Happy Pharmacy is here to support you with:
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Regulated healthcare oversight
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Personalised care
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Trusted online services
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Safe medication supply
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Human support with digital convenience
Conclusion: Your Weight Loss Journey Starts Here
Mounjaro is the most powerful weight loss injection currently available in the UK. Clinical trials prove its effectiveness in life-changing weight reduction.
You don’t have to wait for the NHS or face barriers to care. Happy Pharmacy makes access simple, safe, and professional.
Ready to start your transformation?
Begin with a simple online consultation and take control of your health and confidence today.
Blog medically reviewed by : Palvinder Deol, GPhC Registered Pharmacist, 12 July 2025
References
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Diabetes UK. (2025). Mounjaro - Uses, How it Works and Side Effects
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MHRA. (2023). MHRA authorises diabetes drug Mounjaro (tirzepatide) for weight management and weight loss
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Jastreboff, A. M., et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity. NEJM, 387(3), 205–216. DOI
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Eli Lilly and Company. (2023). Tirzepatide shows additional 21.1% weight loss
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Medical News Today. (2024). Mounjaro peak effects: How long it takes to work
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NCBI Bookshelf. (2024). Tirzepatide - StatPearls
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