The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
Mounjaro Timeline: Week-by-Week Expectations
If you're considering Mounjaro (tirzepatide) for weight management in the UK, understanding the timeline is essential. Mounjaro is a prescription-only, once-weekly injection that works gradually over several months. This guide explains what happens at each stage, from your first injection through to maintenance, helping you know what to expect on your weight loss journey.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How the Mounjaro Dose Escalation Timeline Works
Mounjaro follows a structured dose titration schedule designed to help your body adjust gradually whilst minimising side effects. Here's the standard UK timeline:
- Weeks 1–4 (2.5 mg): Starting dose. You'll receive one pre-filled KwikPen injection per week. This is a low dose used to assess tolerance and allow your body to adapt to the medication.
- Weeks 5–8 (5 mg): First escalation. Your prescriber will increase the dose after at least 4 weeks if side effects are manageable. Many people begin noticing appetite suppression at this stage.
- Weeks 9–12 (7.5 mg): Second escalation if needed. Your prescriber may increase further depending on your response and any side effects you've experienced.
- Weeks 13–16 (10 mg): Third escalation option. By this point, you've been on Mounjaro for approximately 4 months and may be seeing measurable weight loss.
- Weeks 17–20 (12.5 mg): Higher maintenance dose. Your prescriber assesses whether further escalation is appropriate.
- Week 21+ (15 mg): Maximum dose. This is the highest available dose of Mounjaro. You remain on this dose as your maintenance level unless your prescriber adjusts it.
The entire escalation process from 2.5 mg to 15 mg typically takes approximately 5–6 months. Individual timelines may vary based on how well you tolerate each dose.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
What to Expect at Each Stage of Your Timeline
Weeks 1–4 (Starting): Nausea is common but typically mild. Appetite may begin to reduce. Weight loss is usually modest. You're still adjusting to the medication.
Weeks 5–12 (Early escalation): Side effects often peak around weeks 5–8 then improve. Appetite suppression becomes more noticeable. Initial weight loss accelerates slightly. Many people report reduced food cravings.
Weeks 13–20 (Mid to late escalation): Side effects typically stabilise or diminish. Weight loss becomes more consistent. Energy levels often improve. You may notice changes in how full you feel after smaller meals.
Week 21+ (Maintenance): Your body has adjusted to Mounjaro. Weight loss continues but at a steadier pace. Most people tolerate their maintenance dose well. Regular check-ins with your prescriber ensure you're on the right dose for you.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
How long before Mounjaro starts working?
Most people notice reduced appetite within the first 2–4 weeks, though some changes are subtle. Measurable weight loss typically becomes apparent around weeks 4–8 as your dose increases and your body fully adjusts. Results vary — some people see changes sooner, others take longer. Individual weight loss depends on diet, activity, and your personal response to the medication.
Can I skip from 2.5 mg directly to a higher dose?
No. Mounjaro requires a structured escalation schedule where you must stay on each dose for at least 4 weeks before increasing. This is important for tolerability and safety. Skipping doses or escalating faster can increase side effects without improving results. Your prescriber will manage your specific timeline based on how you respond.
What if I experience severe side effects during the timeline?
Contact your prescriber immediately. You may pause escalation, stay on your current dose longer, or in rare cases, reduce your dose. Side effects often improve with time, but your prescriber may adjust your timeline to suit you. Never stop Mounjaro without medical guidance — discuss any concerns with your GP or the prescriber managing your tirzepatide.
When should I see weight loss results on Mounjaro?
Clinical trials showed average weight loss of 15–21% body weight over 72 weeks with proper dose escalation and lifestyle changes. However, timelines vary significantly. Some people see initial weight loss within weeks 5–12, others see steady changes from week 16 onwards. Try our GLP-1 weight loss calculator to see potential projections, though your actual timeline may differ.
Is the timeline different on the NHS versus private prescription?
The medication timeline is the same — dose escalation follows the same 4-week intervals regardless of whether you're on NHS or private prescription. However, NHS waiting times for specialist weight management services can be long in some areas, meaning your start date may be delayed. Private prescribing may begin sooner, but the actual treatment timeline remains identical once you start injecting.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.