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
What Are the Main Problems With Mounjaro in the UK?
Mounjaro (tirzepatide) is an effective weight loss injection for many UK adults, but it's not without challenges. Common problems include gastrointestinal side effects, dose titration difficulties, access barriers through the NHS, and concerns about cost and long-term use. Understanding these issues helps you make an informed decision with your GP about whether this prescription medication is right for you.
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.
Side Effects and Medical Concerns With Mounjaro
The most frequently reported Mounjaro side effects in the UK include nausea, vomiting, diarrhoea, and constipation — especially during dose titration when increasing from 2.5 mg to higher doses. Many patients experience stomach pain and indigestion that can persist for weeks. Some users report significant appetite suppression leading to inadequate nutritional intake, whilst others develop injection site reactions or hair loss (alopecia).
Serious but rare problems include pancreatitis (severe abdominal pain), gallbladder issues, and changes in heart rate. The tirzepatide formulation's dual GIP and GLP-1 mechanism means it may affect oral medication absorption — contraceptive pills, for example, require additional barrier protection for 4 weeks after starting and after each dose increase.
- Nausea and vomiting can last several weeks, affecting quality of life
- Dose titration requires patience — minimum 4 weeks per dose before escalation
- Gastroparesis (delayed stomach emptying) may worsen in susceptible individuals
- Cost of side effect management (anti-nausea medications) adds to overall expense
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 Problems and Eligibility Barriers
In the UK, accessing Mounjaro through the NHS is significantly challenging. NICE approved tirzepatide for use in specialist tier 3 weight management services, but availability is severely limited by region — some NHS integrated care boards (ICBs) offer no access at all, whilst others have waiting lists of 18+ months. GP referral to specialist services is the only NHS route, and many GPs lack familiarity with tirzepatide prescribing in UK practice.
Eligibility requires a BMI of 30+ (or 27+ with weight-related health conditions), but meeting criteria doesn't assures access — budget constraints and service capacity often prevent prescribing even for eligible patients. Many people resort to private prescribing because NHS delays are unacceptable, creating equity issues and widening access disparities across the UK.
- NHS waiting lists can exceed 12–24 months in many regions
- Private alternatives cost £150–£320 monthly depending on dose
- Treatment discontinuation due to cost creates yo-yo weight patterns
- 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 is the most common problem with Mounjaro that patients report?
Nausea and gastrointestinal distress are the most frequently reported problems, particularly during dose titration. Most patients experience some nausea in weeks 1–4, though it typically improves. Using our free GLP-1 weight loss calculator can help you understand expected outcomes and whether the side effect profile might be manageable for your situation.
Can I get Mounjaro through the NHS in the UK?
Mounjaro is available through NHS specialist tier 3 weight management services, but access is extremely limited by region. Some areas have 18+ month waiting lists or no availability. You must be referred by your GP and meet eligibility criteria (BMI 30+ or 27+ with comorbidities). Many eligible patients never receive NHS treatment due to service capacity constraints.
What happens if I stop taking Mounjaro?
Weight typically returns gradually once treatment stops because Mounjaro addresses appetite regulation, not underlying eating patterns. Many patients regain 30–50% of lost weight within months. This creates a long-term commitment problem — stopping is difficult, and restarting costs are significant, making sustainability a major concern for many UK users.
Is tirzepatide safer than Wegovy for weight loss?
Both medications have similar safety profiles with gastrointestinal side effects being most common. Mounjaro's dual GIP/GLP-1 mechanism may produce slightly better weight loss outcomes in clinical trials (~20% vs ~15%), but individual results vary considerably. Your GP or prescriber can advise which is more appropriate based on your health history.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs approximately £150–£320 per month depending on dose and pharmacy, with higher doses being more expensive. At maximum dose (15 mg), expect around £280–£320 monthly. This creates financial barriers for many people, particularly since treatment is typically long-term. Compare costs using our GLP-1 calculator to project your likely dose and budget accordingly.
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.