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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Why Is Mounjaro Not Working For Me?
If you've started Mounjaro (tirzepatide) and aren't seeing the weight loss results you expected, there are several reasons this might happen — and several ways to address it. Weight loss on Mounjaro varies significantly between individuals, and sometimes access or dosage adjustments are needed. This guide explains why Mounjaro might not be delivering results for you, how to access it effectively in the UK, and what your options are depending on whether you're using the NHS or private prescription routes.
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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 Reasons Mounjaro May Not Deliver Expected Results
Individual variation is significant. Clinical trials showed average weight loss of 15–21% body weight, but this is an average — some people lose considerably more, others lose less, and a small percentage experience minimal weight loss. Results depend on genetics, baseline metabolism, adherence to the medication, dietary habits, and physical activity levels.
Dose may be too low. Mounjaro starts at 2.5 mg and titrates up to a maximum of 15 mg. If you're on a maintenance dose below 10 mg, you may benefit from discussing a dose increase with your prescriber — though each dose requires a minimum of 4 weeks before escalation. Dose titration should follow the standard protocol: 4 weeks minimum per dose before moving up.
Diet and exercise matter. Mounjaro is not a standalone solution — clinical trial results were achieved alongside a reduced-calorie diet and increased physical activity. If dietary habits haven't changed significantly, weight loss will plateau. Similarly, the appetite-suppressing effects of the medication may diminish over time as your body adapts.
Medical factors. Thyroid disorders, PCOS, certain medications, or hormonal changes can affect weight loss regardless of medication. Your GP should have ruled these out before prescribing.
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.
Accessing Mounjaro in the UK: NHS vs Private Routes
NHS access: NICE has approved tirzepatide for NHS use, but availability is limited to specialist tier 3 weight management services. Referral from your GP is required, and waiting lists in many areas are substantial (sometimes 12+ months). Once accessed, Mounjaro is provided free on the NHS if clinically appropriate.
Private prescription access: You can access Mounjaro privately through a UK-licensed prescriber via online consultation — no NHS referral needed. This typically costs £129–£200 per month depending on your dose (higher doses cost more). Private prescriptions are dispensed by GPhC-registered pharmacies following assessment. The consultation process is quicker (days rather than months), but costs are out-of-pocket.
Online consultation process: You'll complete a detailed health questionnaire, may have a video or phone consultation with a prescriber, and if approved, receive a prescription that's sent to a pharmacy for dispensing. Results are not assured — prescribers will only issue prescriptions if you meet eligibility criteria and have no safety contraindications.
If Mounjaro isn't working and you're on the NHS, discuss with your specialist service about dose adjustment or alternative medications (such as semaglutide, marketed as Wegovy). If accessing privately, speak with your prescriber about whether a dose increase or switch is appropriate. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses — this can help you understand realistic expectations. Additionally, the BMI calculator on this page will help you track changes in your BMI category as you lose weight, even if the scale movement feels slow.
- 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 Mounjaro assured to help me lose weight?
No. Clinical trials showed average weight loss of 15–21% body weight, but individual results vary significantly. Some people lose more, others lose less, and a small percentage experience minimal weight loss. Weight loss depends on genetics, diet, exercise, medication adherence, dose, and other medical factors. Your prescriber can assess your likelihood of success during the eligibility assessment.
How much does Mounjaro cost privately in the UK?
Private Mounjaro typically costs £129–£200 per month, depending on your dose. The 2.5 mg starting dose costs less than the 15 mg maximum dose. Prices vary slightly between different private prescribing services. Online consultations typically cost £15–£50. NHS access is free if you qualify and are referred to a specialist service, though waiting lists can be very long.
Can I switch from Mounjaro to Wegovy if it's not working?
Yes. Both are licensed for weight management in the UK, though they work slightly differently — Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. A switch can be discussed with your prescriber if weight loss stalls. Clinical trial data suggests broadly similar average weight loss outcomes, though individual responses differ. Any medication change requires a prescriber's assessment.
Why does Mounjaro work better for some people than others?
Weight loss medication response depends on multiple factors: genetic predisposition, baseline metabolic rate, adherence to dose schedule, dietary changes, exercise levels, thyroid function, hormonal status, and concurrent medications. Some people's brains respond more strongly to GLP-1/GIP signalling. Your prescriber can explore whether dose adjustment, lifestyle optimisation, or a medication switch might improve outcomes.
Do I need to stay on Mounjaro forever?
Not necessarily. Some people lose their target weight and come off the medication; others maintain long-term use to prevent regain. Clinical evidence suggests weight regain is common after stopping, so ongoing use or robust lifestyle changes are usually needed. This is a conversation to have with your prescriber based on your individual circumstances and goals.
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.