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
How Long Does Mounjaro Take To Work In The UK?
Mounjaro (tirzepatide) typically begins showing weight loss results within 2–4 weeks, with more significant changes visible after 8–12 weeks of consistent use. However, the timeline varies considerably between individuals, and accessing Mounjaro in the UK depends on whether you go through the NHS or private prescription routes. This guide covers realistic timescales, UK costs, and how to get started with this prescription-only weight management injection.
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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.
UK Mounjaro Costs And Private Access Routes
In the UK, Mounjaro is available through private online prescribing without an NHS referral. Private costs typically range from £150–£350 per month, depending on your dose and the provider. The 2.5 mg starting dose is usually the least expensive, while the maximum 15 mg dose costs more. Each Mounjaro KwikPen contains four weekly injections, so monthly supply costs reflect a full four-week cycle. Prices vary between GPhC-registered pharmacies, so it's worth comparing. Private access involves an online consultation with a UK-licensed prescriber, who will assess your eligibility based on BMI, health conditions, and medical history. If approved, your prescription is dispensed by the pharmacy. This route bypasses NHS waiting lists entirely, making it faster than NHS specialist services, though it's a direct out-of-pocket cost.
- Starting dose (2.5 mg): approximately £150–£180/month
- Maintenance doses (5–10 mg): approximately £180–£250/month
- Maximum dose (15 mg): approximately £280–£350/month
- No NHS prescription charge applies — full cost is private
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.
NHS Vs Private: Access And Timeline Differences
Accessing Mounjaro through the NHS is free at the point of use (standard prescription charge applies, currently £9.90 in England), but availability is limited and varies significantly by region. You must be referred to a specialist tier 3 weight management service by your GP, and NHS waiting lists can extend from several months to over a year in many areas. Once approved, NHS-prescribed Mounjaro follows the same dose titration schedule as private prescriptions. The private route is faster — online consultation to prescription typically takes days rather than months — but requires upfront payment. For those seeking rapid access and willing to self-fund, private prescription is the practical choice. Either route involves starting at 2.5 mg and gradually increasing every 4 weeks, meaning visible weight loss results typically emerge around weeks 8–12 regardless of access method. Our GLP-1 weight loss calculator can help estimate potential outcomes at different doses.
- 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 quickly will I see weight loss results with Mounjaro?
Most people notice appetite reduction within 1–2 weeks, but measurable weight loss typically appears after 4–8 weeks. Significant results (5–10% body weight) are often visible by week 12. Individual timescales vary based on dose, diet, activity, and metabolism. Your prescriber will monitor progress at each dose increase.
Why does Mounjaro take time to work?
Mounjaro works by gradually activating GIP and GLP-1 receptors. You start at a low dose (2.5 mg) and increase every 4 weeks to minimise side effects and find your optimal dose. This titration schedule means full effectiveness develops over 16–20 weeks for many users.
What's the difference between NHS and private Mounjaro costs in the UK?
NHS costs £9.90 per prescription (standard charge in England) but involves referral and waiting lists. Private costs £150–£350/month depending on dose, with faster access. Both routes offer the same medication and dosing schedule.
Can I switch from Mounjaro to Wegovy if it's not working?
Yes, your prescriber can switch you to an alternative like Wegovy (semaglutide) if Mounjaro isn't delivering expected results or side effects are problematic. This requires a new prescription and clinical assessment. The two medications have different mechanisms, so individual responses vary.
How do I get Mounjaro prescribed privately in the UK?
Complete an online consultation with a UK-licensed prescriber through a GPhC-registered pharmacy. You'll answer health questions about BMI, weight-related conditions, and medications. If approved, your prescription is dispensed and sent to you. The full process typically takes 2–5 working days.
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.