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
Your First Week on Mounjaro in the UK
Starting Mounjaro (tirzepatide) is an important health decision. Your first week involves receiving your 2.5 mg starter dose, understanding how to store and inject your KwikPen, and knowing what to expect physically. This guide covers everything you need to know about accessing Mounjaro in the UK, the costs involved, and what your first week looks like. Whether you're considering NHS or private prescription routes, understanding both your options helps you make an informed choice about this prescription-only weight management injection.
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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.
UK Access Routes and Costs for Mounjaro
Mounjaro is available in the UK through two main routes: NHS specialist weight management services and private prescription via registered online prescribers.
NHS route: If eligible, your GP can refer you to a tier 3 specialist weight management service. NICE has approved tirzepatide for NHS use, but availability varies significantly by region and ICB. Waiting lists can extend several months. There is no direct cost to you at point of prescribing, though the medication remains funded through NHS budgets.
Private route: Available through GPhC-registered online pharmacies following a clinical consultation. Costs typically range from £129 to £320 monthly depending on your dose. The 2.5 mg starter dose costs less than maintenance doses (5–15 mg). You pay for the full course yourself. Private prescribing offers faster access without NHS waiting lists, though individual assessment is still required.
- NHS: Free but longer waiting times; regional variation in availability
- Private: £129–£320 per month; access within days of prescription
- Both routes require clinical assessment confirming eligibility
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.
What to Expect in Your First Week
Your first dose (2.5 mg) arrives as a pre-filled KwikPen containing four weekly injections. Store unopened pens in your fridge at 2–8°C. You'll inject once weekly, rotating injection sites between your stomach, thighs, or upper arms. Most people experience mild nausea in the first week—this typically reduces as your body adapts. Keep a food diary and eat smaller, lighter meals to manage early side effects.
Use our GLP-1 weight loss calculator to understand realistic first-week expectations: weight loss is minimal in week one (the medication is still building in your system), but this establishes your baseline. Your prescriber should provide injection training or clear written guidance. Contact them immediately if you experience severe stomach pain or allergic symptoms. Many people find the first week straightforward once they understand the injection technique.
Your first dose (2.5 mg) arrives as a pre-filled KwikPen containing four weekly injections. Store unopened pens in your fridge at 2–8°C. You'll inject once weekly, rotating injection sites between your stomach, thighs, or upper arms. Most people experience mild nausea in the first week—this typically reduces as your body adapts. Keep a food diary and eat smaller, lighter meals to manage early side effects.
Try our GLP-1 weight loss calculator to understand realistic expectations over your first weeks on treatment. Weight loss is often minimal in week one while the medication builds in your system, but this establishes your baseline. Your prescriber should provide injection training or clear written guidance. Contact them immediately if you experience severe stomach pain or allergic symptoms. Many people find the first week straightforward once they understand the injection technique.
- 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.
How much does Mounjaro cost privately in the UK for my first dose?
Private Mounjaro costs vary by provider, but the 2.5 mg starter dose typically costs £129–£180 for a four-week supply (four injections). Prices increase slightly for higher maintenance doses (5 mg upwards). Check current pricing with registered providers; costs may differ by location and service.
Can I get Mounjaro free on the NHS?
Yes, if referred to an NHS tier 3 specialist weight management service and assessed as eligible. However, NHS availability varies greatly by region and waiting lists are often several months. Your GP can advise whether your local ICB funds tirzepatide and what the waiting time might be.
What happens during a private online consultation for Mounjaro?
You complete a health questionnaire covering your medical history, current medications, and weight management goals. A UK-licensed prescriber reviews this and assesses your eligibility. If approved, a prescription is issued to a GPhC-registered pharmacy, which dispatches your first KwikPen within 1–3 days.
Is there a difference between NHS and private Mounjaro?
No—the medication itself is identical. The difference is access speed (private is faster), cost (NHS is free to you), and how it's prescribed (NHS via specialist referral, private via online assessment). Effectiveness and side effects are the same.
What should I do if I experience side effects in my first week?
Mild nausea, constipation, and reduced appetite are common and usually settle within days. Eat smaller, lighter meals and stay hydrated. If you experience severe stomach pain, persistent vomiting, or signs of allergic reaction, contact your prescriber or GP immediately.
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.