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 Side Effects, Cost & How to Access in the UK
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection licensed in the UK. Before considering this GLP-1 receptor agonist treatment, it's important to understand both the potential side effects and the practical aspects of accessing it—including cost and whether it's available through the NHS or private providers. This guide covers what you need to know about Mounjaro side effects alongside UK access routes and pricing information.
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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 Side Effects & UK Private Prescription Costs
Mounjaro side effects are common, especially during the first four weeks of treatment. The most frequently reported effects include nausea, diarrhoea, vomiting, constipation, and abdominal pain—experienced by more than 1 in 10 users. These gastric symptoms often improve as your body adjusts to the weekly injection.
When accessing Mounjaro privately in the UK, costs vary by dose and provider. A typical private prescription costs between £150–£300 per month, depending on your current dose. Each KwikPen contains four weeks of injections. Starting doses (2.5 mg) are usually at the lower end of this range, while maximum doses (15 mg) cost more. Private prescribers assess your eligibility through an online consultation, and if approved, your prescription is dispensed by a GPhC-registered pharmacy.
Less common but serious side effects requiring medical attention include severe stomach pain (possible pancreatitis), gallbladder problems, or serious allergic reactions. Hair loss (alopecia) has been reported by some users but is not common.
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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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NHS vs Private: Your UK Access Options
In the UK, you can access Mounjaro through two routes. NHS access is through specialist tier 3/4 weight management services—you'll need a GP referral, and availability varies significantly by region and ICB funding. Waiting lists for NHS specialist services can be several months or longer in many areas. Private access is faster: you have an online consultation with a UK-licensed prescriber, receive a prescription if clinically appropriate, and collect your medication from a GPhC-registered pharmacy without NHS referral.
For private treatment, expect to complete an online health questionnaire and video or phone consultation. Your prescriber will assess your BMI, medical history, and current medications. If eligible, your first prescription is issued within 24–48 hours. Use our GLP-1 weight loss calculator to project potential weight loss at different doses—this can help inform your discussion with a prescriber.
Mounjaro storage requires refrigeration (2–8°C) until first use, then room temperature for up to 30 days. Private providers typically deliver directly to your home. On the NHS route, once referred to a specialist service, you'll have appointments to monitor your progress, adjust doses, and manage any side effects—adding to the overall timeline but providing closer medical support. Your choice depends on urgency, regional NHS availability, and budget.
- 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 in the UK?
Nausea, diarrhoea, vomiting, constipation, and stomach pain are most common, especially in the first 4 weeks. They usually improve as your body adjusts. Less common effects include fatigue, dizziness, indigestion, and injection site reactions. Always report persistent or severe symptoms to your prescriber.
How much does Mounjaro cost privately in the UK?
Private Mounjaro prescriptions typically cost £150–£300 per month depending on your dose. Starting doses (2.5–5 mg) are usually around £150–£180, while higher maintenance doses (10–15 mg) cost £250–£300. Each KwikPen contains 4 weeks of injections. Prices vary slightly between providers.
Can I get Mounjaro on the NHS in the UK?
Yes, but only through specialist tier 3/4 weight management services with a GP referral. Availability and waiting times vary significantly by region—some areas have waits of several months. Private prescription is faster but requires payment. Your GP can advise on NHS availability in your area.
How long does it take to get Mounjaro through private prescription?
Private access is typically much faster than NHS. After your online consultation, if approved, you'll receive a prescription within 24–48 hours and medication is usually delivered within 2–5 working days. Total time from consultation to first injection is often 5–7 days.
What should I do if I experience severe side effects from Mounjaro?
Seek immediate medical attention if you experience severe stomach pain (possible pancreatitis), gallbladder pain, serious allergic reactions, or significant vision changes. Contact your prescriber or GP immediately. Do not wait for your next appointment. Most common side effects improve within 4 weeks, but persistent nausea or other effects should be reported to your healthcare provider.
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.