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
When Is the Best Time to Start Mounjaro in the UK?
There's no single "best time" to start Mounjaro — the right moment depends on your individual health circumstances, NHS eligibility, and readiness to commit to lifestyle changes. However, understanding when you might be eligible and how the NHS and private routes work can help you make an informed decision. Mounjaro (tirzepatide) is a prescription-only injection licensed in the UK for weight management in adults, and starting it requires a clinical assessment to confirm suitability for your specific situation.
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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.
NHS Eligibility and Timing Considerations
NHS eligibility criteria determine whether you can access Mounjaro through the NHS. You may be eligible if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, sleep apnoea, or a history of cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher health risks at lower weights.
The NHS tier 3 specialist weight management services are where Mounjaro prescriptions are typically initiated. However, access varies significantly by region, and waiting lists can be lengthy in many areas. The timing of NHS access depends on:
- Your GP referral to specialist services
- Regional availability and service capacity
- Assessment by the specialist team
- Whether lifestyle interventions have been attempted first
NICE has approved tirzepatide for NHS use, but not all regions have implemented services equally. Check your local Integrated Care Board (ICB) website for current NHS Mounjaro availability in your area.
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.
Readiness Factors and the Private Route
Beyond NHS eligibility, consider your personal readiness before starting Mounjaro. This medication works best alongside a reduced-calorie diet and increased physical activity — it supports weight loss but is not a standalone solution. You should be prepared for potential side effects, particularly nausea and gastrointestinal changes in the first few weeks, which usually improve as your body adjusts.
If NHS waiting times are prohibitive, private prescribing offers faster access. Through a UK-licensed prescriber and GPhC-registered pharmacy, you can have a clinical assessment and prescription within days rather than months. Many people choose the private route when they are motivated to start immediately and can manage the cost. Regardless of route, start Mounjaro when you are genuinely ready to commit to the lifestyle changes that make it effective. Use our free GLP-1 weight loss calculator to explore potential outcomes and our BMI calculator to confirm your eligibility status.
- 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.
Can I start Mounjaro immediately if I meet the eligibility criteria?
Not on the NHS — you'll need a referral to tier 3 services and an assessment, which can take weeks or months depending on your region. Privately, you can start within days after a clinical assessment confirms suitability. Regardless of route, you cannot start without a prescription and clinical evaluation.
Is there a minimum weight loss needed before starting Mounjaro?
No — you don't need to lose weight first. However, the NHS typically expects you to have tried lifestyle interventions (diet, exercise, behaviour change programmes) before prescription medication is considered. Private prescribers may also assess whether you've made genuine attempts at lifestyle changes.
Should I start Mounjaro before or after trying other weight loss methods?
The NHS pathway recommends lifestyle approaches first (tier 1–2 services), then medication if these haven't achieved sufficient results. However, if you have weight-related health complications like type 2 diabetes, starting Mounjaro sooner may be appropriate. Discuss this with your GP or a prescriber to determine the right sequence for your situation.
What if I'm not sure I'm ready to start Mounjaro?
Being ready means committing to reduced-calorie eating and increased activity — Mounjaro helps but doesn't replace these. If you're uncertain, work with your GP or a weight management service to build confidence first. Starting when unmotivated often leads to discontinuation without achieving results.
Does the time of year matter for starting Mounjaro?
Not medically — you can start any time. However, many people find winter easier for focusing on diet and exercise, whilst others prefer starting in spring or summer for motivational reasons. Choose a time when you're mentally prepared and can commit to the full treatment journey, which typically lasts months.
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.