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 Are Monjaro Jabs?
Monjaro jabs are prescription-only weekly injections containing tirzepatide, a medication licensed in the UK for weight management in adults. Unlike older weight loss treatments, Monjaro works as a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways that help regulate appetite, reduce food cravings, and support feeling fuller after meals. The medication comes in a pre-filled KwikPen device and is administered once weekly. Clinical trials showed that people using Monjaro alongside diet and exercise changes lost an average of 15–21% of their body weight, though individual results vary significantly. This guide explains how Monjaro works, who may be eligible, doses, side effects, and how to access it in the UK.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Monjaro Jabs Work in Your Body
Monjaro jabs contain tirzepatide, which mimics two natural hormones: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). These hormones are produced in the gut after eating and signal to your brain that you're satisfied. By activating both pathways simultaneously, tirzepatide may help regulate appetite more effectively than single-hormone medications like Wegovy (semaglutide).
When you inject Monjaro, it:
- Reduces hunger signals sent to your brain
- Helps you feel fuller after eating smaller portions
- Slows how quickly food leaves your stomach (gastric emptying)
- Helps your body use energy from fat more efficiently
This dual-action mechanism is what distinguishes Monjaro from older GLP-1 receptor agonist treatments. The medication is not insulin — it doesn't work the same way and is suitable for people without diabetes. Individual response varies; some people notice appetite suppression within days, while others take weeks to feel the full effect.
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.
Monjaro Jab Doses and How to Use Them
Monjaro comes in doses ranging from 2.5 mg to 15 mg, injected once weekly under the skin. Treatment starts at 2.5 mg for the first 4 weeks, then increases gradually every 4 weeks (to 5 mg, 7.5 mg, 10 mg, 12.5 mg, then 15 mg) depending on how well you tolerate it and your weight loss response.
Each Monjaro KwikPen contains 4 doses (4 weeks' supply). You inject into your stomach, upper thigh, or upper arm, rotating sites each week. The jab takes seconds and uses a tiny needle. Many people store their pen in the fridge (2–8°C) but can keep it at room temperature below 30°C for up to 30 days after first use. If you miss a dose within 4 days, take it as soon as you remember; if longer, skip and resume your normal schedule.
- 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.
Are Monjaro jabs the same as Ozempic?
No. Both Mounjaro and Ozempic (semaglutide) are injectable medications, but Monjaro contains tirzepatide (a dual GIP/GLP-1 agonist), while Ozempic contains semaglutide (GLP-1 only). More importantly, Ozempic is licensed for type 2 diabetes, not weight loss — using it for weight loss is off-label. Wegovy is the UK-licensed semaglutide product for weight management.
How much weight will I lose on Monjaro jabs?
Clinical trials (SURMOUNT-1) showed average weight loss of 15–21% of body weight over 72 weeks when combined with diet and exercise. However, individual results vary significantly — some people lose more, others less. Weight loss depends on your starting weight, adherence to lifestyle changes, genetics, and metabolism. Your prescriber can discuss realistic expectations for your situation.
What are the main side effects of Monjaro jabs?
Very common side effects include nausea, diarrhoea, constipation, vomiting, and stomach pain — usually most noticeable when starting or increasing doses. These often improve over time as your body adjusts. Less common side effects include fatigue, dizziness, headache, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) — seek immediate medical attention if this occurs.
Can I get Monjaro jabs on the NHS in the UK?
Yes, Monjaro (tirzepatide) is approved by NICE for use within NHS specialist weight management services. However, access is through tier 3/4 specialist services — not standard GP prescription — and availability varies significantly by region. Waiting lists can be very long. Alternatively, prescription Monjaro is available privately through online clinical assessments from UK-licensed prescribers, typically costing £150–£250 per dose.
Who cannot use Monjaro jabs?
You cannot use Monjaro if you're pregnant, planning pregnancy, or breastfeeding; under 18 years old; have a severe allergy to tirzepatide; or have severe gastroparesis (stomach paralysis). People with a personal or family history of medullary thyroid cancer or MEN syndrome should not use Monjaro. Always inform your prescriber of all health conditions and medications before starting.
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.