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
Free tracker included with every download this week
Mounjaro Side Effects and UK Access: Cost and Availability Guide
Mounjaro (tirzepatide), commonly referred to as a "weight loss injections" in the media, is a prescription-only weight management injection available in the UK through both NHS specialist services and private prescription routes. Understanding the potential side effects, costs, and how to access this medication is essential before considering whether it's right for you. This guide covers what you need to know about Mounjaro eligibility, access routes, and realistic expectations.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Private Mounjaro Access and Cost in the UK
Private prescription costs for Mounjaro in the UK typically range from £129 to £320 per month, depending on the dose strength and provider. Starting doses (2.5 mg) are usually at the lower end, while higher maintenance doses (10–15 mg) cost more. Each KwikPen contains four weekly injections, so monthly cost reflects one pen per dose level.
- Doses 2.5–5 mg: approximately £129–£180 per month
- Doses 7.5–10 mg: approximately £180–£250 per month
- Doses 12.5–15 mg: approximately £250–£320 per month
Private prescriptions require an online clinical assessment with a UK-licensed prescriber. You'll need to answer health questions, provide weight and height measurements, and discuss any existing medical conditions. The assessment typically takes 24–48 hours, and if approved, your prescription is sent to a GPhC-registered pharmacy for dispensing.
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 vs Private Prescription: What's the Difference?
The NHS route involves referral to a tier 3 specialist weight management service through your GP. NICE has approved tirzepatide for use within NHS services, but availability varies significantly by region and waiting lists can be lengthy—sometimes months or years depending on your local integrated care board (ICB). If you meet eligibility criteria (BMI 30+, or 27+ with weight-related health conditions), your GP can refer you.
The private route is faster but involves upfront costs. You access online prescribing without NHS referral, pay for each prescription privately, and can start treatment within days rather than months. Many people choose private access due to NHS waiting lists. Use our free GLP-1 weight loss calculator to understand potential outcomes with Mounjaro at different dose titration stages.
Common side effects include nausea, diarrhoea, vomiting, and constipation—often most pronounced during dose escalation. Most people adjust within 1–2 weeks as their body acclimates. Serious side effects are rare but include severe stomach pain (possible pancreatitis), gallbladder problems, and allergic reactions. Always report persistent or severe symptoms to your prescriber. Calculate your personal BMI using our free BMI calculator to understand your baseline health status before starting any weight management treatment.
- 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.
How much does Mounjaro cost on the NHS in the UK?
Mounjaro is free on the NHS if prescribed through a specialist tier 3 weight management service. However, access is limited and varies by region. Your GP must refer you, and waiting lists can be several months or longer depending on your local ICB. NHS availability is not assured in all areas.
Can I buy Mounjaro privately without waiting on the NHS?
Yes. Private prescription routes are available through online consultations with UK-licensed prescribers. Costs range from £129–£320 monthly depending on dose. The process is faster—typically approved within 24–48 hours—but you pay privately. Compare expected outcomes using our GLP-1 weight loss calculator before deciding.
What are the main side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, and constipation—usually temporary during dose titration. Less common: fatigue, dizziness, headache, and injection site reactions. Rare serious side effects include pancreatitis (severe stomach pain) and gallbladder issues. Always contact your prescriber about persistent symptoms.
Is Mounjaro the same as Wegovy, and which is cheaper?
Both are prescription-only injections, but Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is GLP-1 only. Mounjaro has shown slightly higher average weight loss in trials. Costs are similar (£129–£320 monthly privately). Mounjaro vs Wegovy choice depends on individual response and prescriber recommendation—not cost alone.
Do I need a prescription to get Mounjaro in the UK?
Yes, Mounjaro is prescription-only in the UK. You cannot buy it over the counter. Access is either through NHS referral to a specialist weight management service or via a private online clinical assessment with a licensed prescriber. Both routes require a valid prescription issued by a UK-qualified healthcare professional.
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.