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
Left Side Pain on Mounjaro — What You Need to Know
Left side pain or stomach discomfort during Mounjaro treatment can be concerning. While common side effects like nausea and constipation are usually mild, severe or persistent abdominal pain — especially pain in the upper left side spreading to the back — may indicate pancreatitis and requires urgent medical attention. This guide explains when to seek help, how to access Mounjaro in the UK, and what costs you can expect through NHS and private routes.
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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.
When Left Side Pain Requires Medical Attention
Most people experience mild digestive side effects on Mounjaro, including stomach discomfort, nausea, and constipation — these typically ease after the first few weeks. However, severe, persistent abdominal pain is not normal and requires immediate assessment. Pancreatitis is a serious but rare side effect of Mounjaro that presents with sudden severe pain in the upper abdomen spreading to the back, often with nausea and vomiting. If you develop this, call 999 or attend your nearest A&E immediately. Other concerning symptoms include pain accompanied by fever, yellowing of the skin or eyes, or rapid heartbeat. Milder left-sided discomfort may relate to the slower stomach emptying that Mounjaro causes, but persistent pain lasting more than a few days should be discussed with your GP. Always contact your prescriber or GP if you are unsure — they can assess whether symptoms are expected side effects or need further investigation.
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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.
Accessing Mounjaro in the UK — Cost and Routes
In the UK, Mounjaro is available through two routes: NHS specialist services and private prescription. NHS access is through tier 3 weight management services, typically requiring a GP referral, though waiting lists vary significantly by region — some areas have waits of 6–18 months. Private route access is faster: online consultations with UK-licensed prescribers take days, with costs ranging from approximately £129–£320 monthly depending on your dose. Monthly costs cover a four-week supply (four KwikPen injections). Calculate your projected Mounjaro weight loss and costs using our GLP-1 weight loss calculator, and assess your BMI eligibility using our free BMI calculator. Private prescriptions are dispensed by GPhC-registered pharmacies — always verify registration before ordering.
- 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.
Is left side pain a normal Mounjaro side effect?
Mild stomach discomfort is common early on Mounjaro, but severe left-sided pain is not normal. Pancreatitis — a rare serious side effect — causes sudden severe upper abdominal pain spreading to the back. Seek urgent medical attention if pain is severe or persists beyond a few days.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Both are once-weekly injections for weight management. Clinical trials showed Mounjaro achieved slightly higher average weight loss, but individual results vary significantly. Both require prescription and clinical assessment.
How much does Mounjaro cost on the NHS?
Mounjaro is free on the NHS if prescribed through specialist tier 3 services, though access varies by region and requires referral. Many areas have long waiting lists. Private prescription costs range from roughly £129–£320 per month depending on your dose level.
Can I get Mounjaro privately without waiting for NHS?
Yes. Private UK prescribers offer online consultations (usually within days), issuing prescriptions that GPhC-registered pharmacies dispense. You'll need to pay out-of-pocket. Always verify the pharmacy is registered with the GPhC before ordering Mounjaro or tirzepatide.
What should I do if I develop severe abdominal pain on Mounjaro?
Seek immediate medical attention by calling 999 or attending A&E if you develop sudden severe pain in the upper abdomen spreading to the back, especially with nausea, fever, or yellowing of skin. This may indicate pancreatitis. Always inform healthcare professionals you are taking Mounjaro.
Ready to take control of your weight loss journey?
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