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
Can You Start Mounjaro On 5mg In The UK?
No, you cannot start Mounjaro on 5mg in the UK. The standard starting dose is 2.5mg once weekly, regardless of BMI or weight. This lower starting dose allows your body to adjust to the medication and helps your prescriber monitor how well you tolerate it before gradually increasing to maintenance doses. Understanding the correct dosing schedule is essential if you're considering Mounjaro through NHS specialist services or private prescription.
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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.
Why Mounjaro Starts At 2.5mg — The Titration Schedule
Mounjaro follows a four-week dose titration schedule in the UK, starting at 2.5mg and increasing gradually based on tolerance and response. This approach minimises side effects and allows your body to adapt to the medication. The standard escalation pathway is: 2.5mg (weeks 1–4), then 5mg (weeks 5–8), 7.5mg (weeks 9–12), 10mg (weeks 13–16), 12.5mg (weeks 17–20), and finally 15mg (week 21 onwards) as the maximum dose.
Each dose is administered once weekly via the Mounjaro KwikPen — a pre-filled injection device. You must remain on each dose for a minimum of four weeks before increasing, even if you feel you could tolerate a higher dose sooner. Your prescriber will assess your response at each stage, checking side effects, weight loss progress, and overall tolerability before recommending escalation. This careful titration is why Mounjaro treatment typically takes 5–6 months to reach the maximum 15mg dose.
Clinically BackedWeight Loss
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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.
Starting Mounjaro Through NHS Or Private Prescription
In the UK, Mounjaro is available through NHS specialist tier 3 weight management services following referral from your GP, or through private prescription via a licensed online prescriber. Both routes follow the same 2.5mg starting dose — there is no variation based on how you access the medication. NHS access can involve significant waiting lists in many regions, whilst private routes typically provide faster access following an online clinical assessment. Your prescriber — whether NHS or private — will assess your eligibility based on BMI and weight-related health conditions, and will always start you at 2.5mg to ensure safety. Using our GLP-1 weight loss calculator can help you understand potential outcomes once you reach maintenance doses, and our BMI calculator confirms whether you meet eligibility criteria.
- 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.
Will my prescriber let me start Mounjaro at 5mg instead of 2.5mg?
No. All UK prescribers — NHS and private — follow MHRA guidance and best practice by starting at 2.5mg. Starting at a higher dose increases side effects like nausea and vomiting, and prevents proper tolerance assessment. Your prescriber will increase to 5mg only after four weeks at 2.5mg if you're tolerating it well.
Is 2.5mg an effective dose for weight loss?
2.5mg is a starting dose only, not a maintenance dose. Most weight loss occurs at higher doses (10mg–15mg). Clinical trials showed average weight loss of around 15–21% at the maximum 15mg dose. You'll typically see modest weight loss at 2.5mg whilst your body adjusts.
How long until I reach the 5mg dose?
You'll progress to 5mg after four weeks on the 2.5mg starting dose, provided you're tolerating it without significant side effects. Some people may stay on 2.5mg longer if they experience nausea or other side effects that are settling down.
Can I skip doses or jump to a higher dose faster?
No. Skipping the gradual titration schedule is not recommended and your prescriber will not advise this. The four-week intervals between dose increases are based on clinical trial data and safety evidence. Jumping doses significantly increases nausea, vomiting, and other gastrointestinal side effects.
What if I can't tolerate 2.5mg — what happens?
If you experience severe side effects at 2.5mg, contact your prescriber immediately. They may recommend staying on 2.5mg for longer, or in rare cases, pausing treatment to assess whether Mounjaro is suitable for you. Never stop taking Mounjaro without medical guidance.
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.