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
Can You Start Mounjaro on 5mg?
No, you cannot start Mounjaro on 5mg in the UK. The standard starting dose of tirzepatide (Mounjaro) is always 2.5mg once weekly, regardless of your weight or BMI. This lower starting dose helps your body adjust to the medication and reduces the risk of side effects. After four weeks on 2.5mg, your prescriber will typically increase your dose to 5mg, following a structured titration schedule. Understanding the correct dosing pathway is important for knowing what to expect from your prescription.
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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.
Mounjaro Dosing Schedule and Titration in the UK
Mounjaro (tirzepatide) follows a strict dose titration schedule in the UK, meaning your dose increases gradually over several weeks rather than starting at a high dose immediately. The standard pathway is:
- Weeks 1–4: 2.5mg once weekly (starting dose)
- Weeks 5–8: 5mg once weekly
- Weeks 9–12: 7.5mg once weekly
- Weeks 13–16: 10mg once weekly
- Weeks 17–20: 12.5mg once weekly
- Week 21 onwards: 15mg once weekly (maximum dose)
Each dose comes in a pre-filled KwikPen containing four weekly injections. You cannot skip this titration process — your prescriber will not issue a 5mg starting dose. This gradual increase helps your body adapt and minimises nausea and gastrointestinal side effects that are common in the first few weeks. If you experience tolerability issues at any dose, your prescriber may extend your stay on that dose before increasing further.
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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.
UK Cost and Access Routes for Mounjaro
Access to Mounjaro in the UK depends on your chosen route. On the NHS, tirzepatide is available through specialist tier 3 weight management services following a GP referral, though availability and waiting times vary significantly by region. Privately, Mounjaro is available through UK-registered online prescribing services following an online clinical assessment. Private costs typically range from £180–£320 per month depending on your current dose and provider, with higher doses costing more. Each KwikPen (four weeks of injections at one dose) is dispensed separately. Before starting any prescription, you'll need an online consultation with a UK-licensed prescriber who will confirm you meet eligibility criteria — BMI 30 or above, or BMI 27+ with weight-related health conditions. Try our free GLP-1 weight loss calculator to explore 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.
Why doesn't Mounjaro start at a higher dose like 5mg?
The 2.5mg starting dose allows your body to adjust to tirzepatide gradually, reducing the risk of side effects like nausea, diarrhoea, and vomiting. Clinical trials and UK prescribing practice show this stepwise titration is safer and more tolerable than jumping to higher doses immediately. Your dose increases every four weeks if you tolerate it well.
Can I request to skip the 2.5mg dose and start at 5mg?
No. The dose titration schedule is standardised in the UK and your prescriber will not prescribe a higher starting dose. This is because rapid dose escalation significantly increases gastrointestinal side effects and tolerability issues. The gradual increase is evidence-based and mandatory across NHS and private prescribing.
How much weight can I expect to lose on the 5mg dose?
Individual results vary significantly. Clinical trials (SURMOUNT-1) showed average weight loss of approximately 15% body weight on tirzepatide 5mg over 72 weeks, alongside a reduced-calorie diet and increased physical activity. Your personal result depends on your starting weight, adherence, diet, and exercise. Use our GLP-1 weight loss calculator for a personalised estimate.
Is private Mounjaro more expensive at the 5mg dose than lower doses?
Yes. Private Mounjaro costs are dose-dependent — the 5mg dose typically costs more per month than the 2.5mg dose because you're using a higher-dose KwikPen. Costs vary by provider, ranging from approximately £180–£240 for the 5mg dose. Check with your chosen provider for exact pricing at each dose level.
How long do I stay on the 5mg dose before increasing?
You remain on the 5mg dose for a minimum of four weeks (weeks 5–8 of treatment). Your prescriber will then assess your tolerability and weight loss progress before increasing to 7.5mg. If you experience significant side effects, your prescriber may extend your time at 5mg before escalating further.
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.