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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Mounjaro Pens Dosage vs Wegovy — How They Compare
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK, but they work differently and use different dosage schedules. Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. Understanding how their KwikPen dosing differs, and what clinical trial data shows, can help you discuss these options with your GP or a licensed prescriber during your clinical assessment.
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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.
How Mounjaro and Wegovy Dosages Differ
Mounjaro dosing schedule: Starts at 2.5 mg once weekly, escalating by 2.5 mg increments every 4 weeks to a maximum of 15 mg weekly. The KwikPen delivers four doses, lasting 4 weeks.
Wegovy dosing schedule: Starts at 0.25 mg once weekly, escalating more gradually through 0.5 mg, 1 mg, 1.7 mg, and finally 2.4 mg (maximum). Each step takes 4 weeks, with total titration typically 16–20 weeks to reach maintenance.
Mechanism difference: Mounjaro's dual GIP+GLP-1 action may support different satiety pathways than Wegovy's GLP-1-only mechanism. In clinical trials, Mounjaro showed average weight loss of 15–21% body weight, whilst Wegovy showed approximately 15% at maximum dose. Both require a reduced-calorie diet and increased physical activity for optimal results. Individual outcomes vary significantly.
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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.
Which Medication Is Right for You?
Neither Mounjaro nor Wegovy is universally "better"—suitability depends on your individual health profile, medical history, and prescriber assessment. Your GP or licensed prescriber will evaluate your eligibility (BMI ≥30, or ≥27 with weight-related health conditions), review any medications you take, and discuss which option aligns with your health goals.
Key factors in prescriber decisions: Existing medical conditions, oral medication use (Mounjaro may affect oral contraceptive absorption), personal response to GLP-1 medication, and whether you prefer faster or gradual dose escalation. Both are available through NHS specialist weight management services or private online prescribing in the UK. Use our GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to check your starting point.
- 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.
What is a KwikPen and how do I use Mounjaro's version?
A KwikPen is a pre-filled, disposable auto-injection pen. Mounjaro's KwikPen holds 4 doses (4 weeks' supply) at your prescribed strength. You inject once weekly into the stomach, thigh, or upper arm. Each pen is clearly marked with the dose strength (2.5 mg, 5 mg, 10 mg, etc.). Store unopened pens in the fridge at 2–8°C; after first use, they can be kept at room temperature below 30°C for up to 30 days.
How much faster does Mounjaro reach maximum dose compared to Wegovy?
Mounjaro reaches 15 mg (maximum) in approximately 20 weeks, escalating 2.5 mg every 4 weeks from 2.5 mg start. Wegovy reaches 2.4 mg (maximum) in approximately 16–20 weeks, escalating more gradually from 0.25 mg. Mounjaro's higher maximum dose allows for larger weekly amounts, but individual titration may vary based on side effects and prescriber guidance.
Which medication showed better weight loss in clinical trials?
In the SURMOUNT-1 trial, Mounjaro at 15 mg showed average weight loss of approximately 20.9% body weight. In the STEP-1 trial, Wegovy at 2.4 mg showed approximately clinically studied weight loss. However, these are trial averages with participants following reduced-calorie diets and exercise programmes. Individual results vary widely, and direct comparison between trials is not straightforward due to different populations and methodologies.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications must be managed by your prescriber—do not stop or change injections without clinical guidance. Approximate dose equivalencies exist (Wegovy 1.7 mg ≈ Mounjaro 10 mg), but there is no official established conversion chart. Your prescriber will assess whether switching is appropriate and manage the transition safely.
Do I need a prescription to buy Mounjaro or Wegovy pens in the UK?
Yes, both are prescription-only medicines in the UK. You cannot buy them without a valid prescription from a licensed prescriber. Prescriptions are available through NHS specialist tier 3 weight management services (with potential waiting lists) or private online prescribing services following an online clinical assessment. In all cases, a qualified prescriber must review your health before issuing a prescription.
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.