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 Is the Starting Dose of Mounjaro in the UK?
The starting dose of Mounjaro (tirzepatide) in the UK is 2.5 mg, injected once weekly. This introductory dose is used for the first four weeks to allow your body to adjust to the medication. After this initial period, your dose will typically increase gradually over subsequent weeks, depending on your response and tolerance. NICE has approved tirzepatide for UK use within specialist tier 3 weight management services, and all dosing is determined by your prescriber following a clinical assessment. Understanding the titration schedule helps you know what to expect throughout your treatment journey.
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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.
How Mounjaro Dose Titration Works in the UK
Mounjaro uses a structured escalation schedule to minimise side effects and allow your body to adapt. You will spend a minimum of four weeks on each dose before increasing. The standard UK titration follows this pattern: weeks 1–4: 2.5 mg (starting dose); weeks 5–8: 5 mg (first maintenance); weeks 9–12: 7.5 mg; weeks 13–16: 10 mg; weeks 17–20: 12.5 mg; and week 21 onwards: 15 mg (maximum dose). However, your prescriber may adjust this schedule based on your individual response, side effects, or health conditions. Some patients remain on lower doses if they achieve good weight loss results with fewer side effects. Each KwikPen contains four weekly doses, so you'll need a new pen each month. Clinical trials showed that patients on higher doses experienced greater average weight loss, but individual results vary significantly.
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 and Private Prescribing Routes
In the UK, Mounjaro access depends on your route: through NHS tier 3 specialist weight management services, you will be assessed by a multidisciplinary team and doses managed by your specialist prescriber. NHS waiting lists vary significantly by region (ICB), and availability can take months in some areas. Alternatively, private online prescribing services offer faster access following a clinical assessment with a UK-licensed prescriber, with doses available within days. Whichever route you choose, prescription status remains the same — Mounjaro is prescription-only, and your prescriber will determine whether you need dose increases based on your weight loss progress and side effect tolerance. Use our free GLP-1 weight loss calculator to estimate potential results at different doses, and track your progress with our free progress tracker throughout your 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.
Why does Mounjaro start at 2.5 mg if the maximum is 15 mg?
Starting at a low dose allows your body to adjust gradually and reduces the risk of severe side effects like nausea and diarrhoea. The 2.5 mg dose is not therapeutic on its own — it's a tolerance-building phase. After four weeks, escalation begins. This approach improves tolerability and medication compliance.
Can I skip the starting dose and go straight to 5 mg?
No. Your prescriber will always begin with 2.5 mg. Skipping the starting dose significantly increases the risk of severe gastrointestinal side effects and is not recommended. The four-week titration period is a standard safety protocol approved by NICE and the MHRA.
How long does it take to reach the maximum 15 mg dose?
If you increase the dose every four weeks without delays, you will reach 15 mg by week 21 (approximately five months). However, many patients achieve effective weight loss at lower doses (5–10 mg) and may not progress to 15 mg. Your prescriber decides progression based on your individual response.
What if I experience bad side effects on the starting dose?
Tell your prescriber immediately. Side effects often improve after a few days as your body adjusts. Your prescriber may delay dose escalation, recommend dietary adjustments, or continue at a lower maintenance dose if you're achieving good results. Never stop or reduce your dose without medical guidance.
Is the Mounjaro KwikPen dose fixed, or can I adjust it myself?
The KwikPen is pre-filled with a fixed dose — you cannot adjust the amount you inject. Each dose strength comes in a separate pen (2.5 mg, 5 mg, 7.5 mg, etc.). Your prescriber will prescribe the appropriate strength based on your schedule. You simply dial the dose and inject once weekly.
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.