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 Jab Side Effects: What You Need to Know About Cost and Access in the UK
Mounjaro (tirzepatide) is a prescription-only once-weekly weight management injection licensed in the UK. Many people considering this medication want to understand both the potential side effects and how to access it — including what it costs. Whether you're exploring NHS routes or private prescription options, it's important to know what to expect. Our GLP-1 weight loss calculator can help you understand projected outcomes, whilst understanding the full picture of side effects and access helps you make an informed decision about whether this treatment is right for you.
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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.
Common Mounjaro Side Effects and What to Expect
Mounjaro works as a dual GIP and GLP-1 receptor agonist, which means side effects are relatively common, especially during the first few weeks or after dose increases. Very common side effects (affecting more than 1 in 10 people) include nausea, diarrhoea, vomiting, and constipation — these typically settle within days or weeks as your body adjusts. Stomach pain and indigestion are also frequently reported.
Common side effects (up to 1 in 10 people) include injection site reactions like redness or bruising, fatigue, dizziness, and hair loss (alopecia). These are generally mild and manageable. Serious side effects are rare but require urgent medical attention — including severe stomach pain suggesting pancreatitis, serious allergic reactions, or changes in vision. Always contact your GP immediately if you experience severe or persistent symptoms.
- Most side effects improve with time as your body adjusts to the medication
- Starting at the lowest dose (2.5 mg) and titrating gradually reduces severity
- Staying hydrated, eating small frequent meals, and avoiding fatty foods helps manage nausea
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.
UK Costs and How to Access Mounjaro on Prescription
In the UK, you can access Mounjaro through two main routes: NHS specialist services or private prescription. NHS access is through tier 3 specialist weight management services (requiring GP referral) — availability varies significantly by region and waiting lists can be substantial. Private prescription through a UK-licensed online prescriber typically costs £150–£300 per month depending on your dose, as costs reflect the dose strength you're prescribed — starting doses (2.5 mg) are lower than maximum doses (15 mg). Each KwikPen contains 4 weeks' supply. Costs are comparable with Wegovy but lower than some older GLP-1 medications like Saxenda.
An online clinical assessment (usually £20–£50) assesses your eligibility before prescription. This ensures the medication is safe for you based on your health history, weight, and BMI.
The online consultation process is straightforward: complete a health questionnaire, a UK-licensed prescriber reviews your information, and if approved, a prescription is issued to a GPhC-registered pharmacy. You'll receive your KwikPen within 24–48 hours. Both routes require genuine clinical assessment — there is no "prescription without assessment" in the UK market. Using our BMI calculator helps you understand where you sit relative to NHS eligibility thresholds (BMI 30+, or 27+ with weight-related health conditions). Your prescriber will confirm whether you meet criteria and whether this medication is appropriate for your individual health profile.
- 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 are the most common Mounjaro side effects?
Nausea, diarrhoea, vomiting, and constipation are very common, especially in the first few weeks. Most settle within days to weeks. Stomach pain, indigestion, injection site reactions, and fatigue are also common but generally mild. Serious side effects are rare but include severe stomach pain (possible pancreatitis) or serious allergic reactions — seek immediate medical attention if these occur.
How much does Mounjaro cost on private prescription in the UK?
Private Mounjaro typically costs £150–£300 per month depending on the dose strength you're prescribed. Starting doses (2.5 mg) are lower cost than maximum doses (15 mg). Each KwikPen provides 4 weeks' treatment. Prices may vary between providers, so compare options. An initial consultation is usually £20–£50.
Can I get Mounjaro on the NHS?
Yes, Mounjaro is available through NHS specialist tier 3 weight management services for eligible adults (BMI 30+, or 27+ with weight-related health conditions). Access requires GP referral and varies significantly by region. Waiting lists can be lengthy in many areas — private prescription offers faster access if you prefer not to wait.
How do I access Mounjaro on private prescription?
Complete an online health questionnaire with a UK-licensed prescriber, who reviews your eligibility and health history. If approved, a prescription is issued to a GPhC-registered pharmacy and your KwikPen is dispensed within 24–48 hours. This is faster than NHS routes but requires you to cover the cost yourself.
Is Mounjaro the same as tirzepatide or Wegovy?
Mounjaro is the brand name for tirzepatide — a dual GIP and GLP-1 receptor agonist. Wegovy is semaglutide — a GLP-1-only agonist from a different manufacturer. Both are licensed for weight management in the UK but work slightly differently and have different dose ranges. Your prescriber will advise which suits you best based on your health profile.
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.