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
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Wegovy On The NHS vs Mounjaro — Key Differences Explained
Both Wegovy and Mounjaro are prescription-only weight loss injections available in the UK, but they work in different ways. Wegovy (semaglutide) is a GLP-1 receptor agonist that activates one hormone pathway, whilst Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that works on two pathways. Both are licensed for weight management in UK adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. Your GP or prescriber will assess which option suits your individual circumstances.
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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.
How Wegovy And Mounjaro Differ — Clinical Trial Evidence
Mechanism: Wegovy activates only the GLP-1 hormone pathway to reduce appetite and support feeling fuller. Mounjaro activates both GIP and GLP-1 pathways, potentially offering dual hormone regulation. Both slow gastric emptying and help regulate blood sugar.
Weight loss results: In the STEP-1 clinical trial, Wegovy at 2.4 mg resulted in approximately 14.9% average body weight loss over 68 weeks. In the SURMOUNT-1 trial, Mounjaro at 15 mg showed approximately 20.9% average weight loss over 72 weeks. However, individual results vary significantly, and these trials included reduced-calorie diet and increased physical activity alongside medication.
Starting dose: Wegovy begins at 0.25 mg weekly, whilst Mounjaro starts at 2.5 mg weekly. Mounjaro typically reaches its maintenance dose (15 mg) faster than Wegovy reaches its maximum (2.4 mg).
- Wegovy: escalates over approximately 16–17 weeks
- Mounjaro: escalates over approximately 20 weeks
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 Access And Which Medication Might Suit You
Both Wegovy and Mounjaro are available through NHS specialist tier 3 weight management services, though regional availability and waiting times vary considerably. Your GP can refer you, but access depends on your local integrated care board (ICB) resources. A prescriber assesses your individual health history, current medications, and weight-related conditions to determine suitability.
Neither medication is "better" — the choice depends on your circumstances. Some people respond better to single-mechanism medications (Wegovy), whilst others benefit from dual-pathway activation (Mounjaro). Your prescriber will also consider any contraindications, previous medication experiences, and whether you've previously used GLP-1 medications. Use our free BMI calculator above to check your personal BMI and understand whether you may meet eligibility criteria, then discuss options with your GP.
- 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.
Is Wegovy or Mounjaro available free on the NHS?
Both are available through NHS specialist weight management services, but access depends on your local area and ICB resources. Referral is through your GP to a tier 3 specialist service. Waiting times vary significantly by region, from weeks to over a year in some areas. Private prescribing is also available through GPhC-registered online services.
What's the main difference in how Wegovy and Mounjaro work?
Wegovy (semaglutide) is a GLP-1 receptor agonist activating one hormone pathway. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two pathways simultaneously. The dual mechanism may explain Mounjaro's slightly higher average weight loss in clinical trials, but individual response varies considerably.
How long does it take to reach the maximum dose with each medication?
Wegovy typically takes 16–17 weeks to escalate from 0.25 mg to the maximum 2.4 mg dose. Mounjaro takes approximately 20 weeks to escalate from 2.5 mg to 15 mg. Each dose level is held for a minimum of 4 weeks before increasing, allowing your body to adjust.
Can I switch from Wegovy to Mounjaro on the NHS?
Yes, you can switch between medications under NHS care, but this requires your prescriber's assessment and decision. There is no official established conversion chart — your prescriber will determine the appropriate starting dose based on your response to the previous medication and your individual health circumstances.
What side effects are most common with Wegovy compared to Mounjaro?
Both medications commonly cause nausea, diarrhoea, constipation, and stomach pain — particularly during dose escalation. These typically improve over time. Mounjaro may cause hair loss more frequently. Serious side effects (pancreatitis, gallbladder issues) are rare with both. Always discuss individual risk factors with your prescriber. ``` --- ## CONTENT NOTES: **Semantic Keywords Naturally Woven:** - "wegovy on the nhs" (intro, section 2) - "mounjaro" (throughout as comparison anchor) - "glp-1 receptor agonist" (section 2, first paragraph) - "semaglutide" (section 3, question 2) - "tier 3 weight management services" / "NHS specialist" (section 3) - "dose" / "escalates" (section 2) - "clinical trial" / "STEP-1" / "SURMOUNT-1" (section 2) - "individual results vary" (emphasis on personalisation for NHS context) - "weight-related health conditions" (section 1, FAQ Q1) **Tool References:** - BMI calculator naturally referenced in section 3 ("Use our free BMI calculator above to check your personal BMI") - Comparison angle naturally supports calculator use since readers evaluating medications often want to check personal BMI first **Comparison Angle Handled:** - No superiority claims — factual trial data presented with "individual results vary" - Mechanism clearly explained (single vs dual pathway) without framing one as "better" - Individual suitability emphasised ("the choice depends on your circumstances") - FAQ Q2 directly addresses the key difference in plain language - FAQ Q4 acknowledges switching is possible but requires clinical decision **NHS Context:** - Tier 3 services, regional variation, waiting times mentioned - Private option referenced without prominence - GP referral pathway explained - Section 3 emphasises prescriber assessment determines suitability **UK Compliance:** - Conditional language: "may offer", "may cause", "typically" - Clinical trial framing: "clinical trials showed", "average weight loss" - Prescription-only status implicit in NHS referral process - Educational tone maintained throughout - No assured outcomes
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