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
Do You Need Blood Tests for Mounjaro?
Yes, blood tests are typically required before starting Mounjaro and at regular intervals during treatment. These tests help your prescriber assess whether tirzepatide is safe for you and monitor your health whilst using this prescription-only weight management injection. Your GP or the prescriber conducting your clinical assessment will arrange these tests as part of standard medical practice in the UK.
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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.
Blood Tests Before Starting Mounjaro
Before you can be prescribed Mounjaro, your prescriber will usually arrange baseline blood tests to check your general health and ensure the medication is appropriate for you. These typically include:
- Full blood count (FBC) — checks red cells, white cells, and platelets
- Urea and electrolytes (U&Es) — assesses kidney function
- Liver function tests (LFTs) — checks how well your liver is working
- Fasting blood glucose or HbA1c — measures blood sugar control (especially important if you have prediabetes or type 2 diabetes)
- Lipid profile — checks cholesterol and triglycerides
- Thyroid function (TSH) — important because GIP/GLP-1 agonists can affect thyroid health in some people
If you have a history of pancreatitis or gallbladder problems, additional tests may be arranged. Your prescriber will explain which tests are relevant to your individual health profile before you start tirzepatide.
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.
Monitoring During Mounjaro Treatment
Once you begin Mounjaro treatment, your prescriber will arrange regular follow-up appointments with repeat blood tests, typically every 3–6 months depending on your dose and health status. These monitoring tests check that Mounjaro is working safely and that your blood sugar, kidney function, and liver function remain healthy. If you experience severe stomach pain, signs of pancreatitis, or unusual symptoms, contact your GP immediately — additional blood tests may be needed. Your prescriber may also request blood tests if you develop new health conditions or if your weight loss response changes significantly. Track your progress and health markers using our free progress tracker to share with your healthcare team.
- 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.
What blood tests do I need before starting Mounjaro?
Standard pre-treatment blood tests typically include full blood count, kidney and liver function tests, fasting glucose or HbA1c, lipid profile, and thyroid function. Your prescriber will confirm which tests are needed based on your individual health. These form your baseline for monitoring during treatment.
How often are blood tests needed while taking Mounjaro?
Follow-up blood tests are usually arranged every 3–6 months whilst you're on Mounjaro. The exact frequency depends on your dose, how you're responding to treatment, and your underlying health conditions. Your prescriber will advise you on the schedule.
Can I get blood tests through my GP for Mounjaro monitoring?
Yes, if your GP is managing your Mounjaro treatment, they can arrange blood tests through the NHS. If you've obtained Mounjaro privately, your private prescriber may arrange tests through a private clinic or direct you to use your GP for routine monitoring.
What if my blood tests show abnormal results on Mounjaro?
Your prescriber will review any abnormal results with you. Depending on the findings, they may continue treatment, adjust your dose, arrange additional tests, or recommend stopping Mounjaro. Never stop taking Mounjaro without discussing results with your prescriber first.
Is Mounjaro safe if I have diabetes — will it affect my blood sugar tests?
Mounjaro can help lower blood sugar in people with type 2 diabetes, which is beneficial. However, if you're also taking diabetes medications like insulin or sulphonylureas, your doses may need adjustment. Your prescriber will monitor your HbA1c and discuss any medication changes to keep you safe.
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.