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 the Active Ingredients in Mounjaro?
Mounjaro (tirzepatide) is a prescription-only weight management injection available in the UK through NHS specialist services and private prescribing. The active ingredient is tirzepatide, a dual GIP and GLP-1 receptor agonist — a synthetic hormone that mimics two natural gut hormones. Unlike some weight loss medications, Mounjaro does not contain herbal or "natural" plant extracts; it is a laboratory-synthesised pharmaceutical compound designed to help regulate appetite and support weight loss when used alongside dietary and lifestyle changes.
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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 Tirzepatide Works as Mounjaro's Active Ingredient
Tirzepatide is the single active pharmaceutical ingredient in Mounjaro. It works by activating two hormone pathways simultaneously: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). Both are natural hormones your gut produces after eating.
- GLP-1 action: Signals to your brain that you're full, slows stomach emptying, and helps regulate blood sugar
- GIP action: Works on fat storage and utilisation, supporting metabolic health
- Combined effect: This dual mechanism may help reduce appetite, decrease food cravings, and support feeling satisfied after smaller meals
Tirzepatide is synthesised in a laboratory — it is not extracted from plants or animal sources. Each Mounjaro KwikPen contains tirzepatide dissolved in solution, ready for once-weekly injection. Try our free GLP-1 weight loss calculator to see how tirzepatide-based treatment might support your weight loss goals at different doses.
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.
Mounjaro Inactive Ingredients and NHS Prescribing Context
In addition to tirzepatide, each Mounjaro KwikPen contains inactive ingredients (also called excipients): sodium chloride, disodium phosphate dihydrate, sodium dihydrogen phosphate dihydrate, water for injections, and sodium hydroxide or hydrochloric acid for pH adjustment. These ingredients help keep the medication stable and sterile but have no therapeutic effect.
In the UK, Mounjaro is prescribed through NHS tier 3 specialist weight management services or privately via licensed prescribers. NICE has approved tirzepatide for use in weight management. Your GP can refer you to a specialist service, though waiting times vary significantly by region. Private prescribing offers faster access but requires payment. Eligibility is based on BMI and health factors — use our free BMI calculator to check where you fall on the NHS scale.
- 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.
Is Mounjaro made from natural ingredients?
No. Mounjaro's active ingredient is tirzepatide, a laboratory-synthesised pharmaceutical compound. It is not derived from plants or natural sources. However, tirzepatide mimics the structure and action of natural GLP-1 and GIP hormones your body produces naturally.
What are the inactive ingredients in Mounjaro?
Mounjaro contains sodium chloride, disodium phosphate, sodium dihydrogen phosphate, water for injections, and pH adjusters (sodium hydroxide or hydrochloric acid). These are stabilising ingredients that help keep the medication safe and effective but do not contribute to weight loss.
How does tirzepatide differ from other weight loss medications?
Tirzepatide (Mounjaro) is a dual GIP and GLP-1 agonist, meaning it activates two hormone pathways. Wegovy (semaglutide) activates only the GLP-1 pathway. In clinical trials, tirzepatide showed slightly higher average weight loss (~21% vs ~15%), though individual results vary significantly.
Can I get Mounjaro on the NHS in the UK?
Yes, NICE has approved tirzepatide for NHS use through specialist tier 3 weight management services. You need a GP referral and must meet eligibility criteria (BMI ≥30 or ≥27 with weight-related health conditions). NHS availability and waiting times vary significantly by region.
What should I do if Mounjaro's ingredients cause a reaction?
If you experience an allergic reaction (swelling of lips, tongue, or throat), seek immediate medical attention or call 999. Before starting Mounjaro, inform your prescriber of any allergies. Your GP or prescriber can assess whether this medication is safe for you.
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.