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 2.5 vs 5 mg: Which Dose for Weight Loss?
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection licensed in the UK that works through dual GIP and GLP-1 receptor activation. The starting dose is 2.5 mg and most patients progress to a 5 mg maintenance dose after four weeks. Understanding the differences between these two doses—and how they compare to alternatives like Wegovy—can help you discuss options with your prescriber. Both doses require a clinical assessment and must be prescribed by a UK-licensed healthcare professional.
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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 2.5 vs 5 mg: Dosing, Trials, and Mechanism
Mounjaro 2.5 mg is the starting (induction) dose, taken for the first four weeks. It allows your body to adjust to the medication and helps prescribers assess tolerability. This is not typically a long-term maintenance dose.
Mounjaro 5 mg is the first maintenance dose, introduced at week 5. Clinical trial data from SURMOUNT-1 showed patients at 5 mg achieved an average weight loss of approximately 15% body weight over 72 weeks, compared to placebo.
In contrast, Wegovy (semaglutide) is a GLP-1 agonist only—not a dual mechanism—and showed approximately 14.9% average weight loss at its maximum dose (2.4 mg) in the STEP-1 trial. The key difference: Mounjaro activates both GIP and GLP-1 pathways, whereas Wegovy activates GLP-1 only. This dual mechanism may contribute to slightly higher average weight loss in trials, though individual results vary significantly.
Both are weekly weight loss injection options available as a KwikPen and require prescription through NHS specialist services or private prescribing in the UK.
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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.
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Suitability and Side Effects: Your Prescriber Decides
Whether you start on Mounjaro 2.5 mg depends on individual factors: BMI, existing health conditions, medication interactions, and tolerability. Your prescriber will assess your clinical suitability before prescribing.
Common side effects are similar across doses and include nausea, diarrhoea, constipation, and stomach pain—often mild and temporary as your body adjusts. Serious side effects (severe stomach pain, gallbladder issues, allergic reactions) are rare but require immediate medical attention.
Both Mounjaro and Wegovy work best alongside a reduced-calorie diet and increased physical activity. Use our GLP-1 weight loss calculator to estimate potential outcomes, our BMI calculator to check your starting point, and our progress tracker to monitor your journey if prescribed either medication.
- 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.
Do I start on Mounjaro 2.5 mg or jump to 5 mg?
You always start on 2.5 mg for the first four weeks. This allows your body to adjust and helps your prescriber monitor tolerability. After four weeks, the dose typically increases to 5 mg. Dose escalation must be managed by your prescriber—never adjust on your own.
Is Mounjaro 5 mg better than Wegovy for weight loss?
Clinical trials suggest slightly higher average weight loss with Mounjaro 5 mg (~15%) versus Wegovy 2.4 mg (~14.9%), but individual results vary considerably. Both are effective. Your prescriber will recommend based on your personal health profile, not trial averages.
How much weight can I expect to lose on Mounjaro 2.5 mg?
The 2.5 mg starting dose is not intended as a long-term dose—it's the first four weeks only. Most weight loss occurs at higher maintenance doses (5 mg and above). Your prescriber will escalate your dose if appropriate and monitor your progress.
What's the difference between Mounjaro and Wegovy mechanisms?
Mounjaro is a dual GIP and GLP-1 agonist—it activates two hormone pathways. Wegovy is a GLP-1 agonist only. The dual mechanism in Mounjaro may explain slightly higher average weight loss in trials, though both require prescription and clinical assessment.
Can I get Mounjaro on the NHS as a weekly weight loss injection?
Mounjaro is available through NHS specialist tier 3 weight management services in some regions, though availability and waiting times vary significantly by area (ICB). Private online prescribing is also available in the UK following clinical assessment. Your GP can advise on local NHS access.
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.