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
How Does Mounjaro Help You Lose Weight?
Mounjaro (tirzepatide) is a prescription weight loss injection that works differently from other weight management medicines. It activates two natural hormone pathways in your body—GIP and GLP-1—to help reduce appetite, decrease food cravings, and support feeling fuller after smaller meals. Clinical trials have shown that Mounjaro may help people lose an average of 15 to 21% of their body weight when used alongside a reduced-calorie diet and increased physical activity. Understanding how this weekly weight loss injection works can help you decide if it's right for your weight loss journey.
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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.
The Dual Hormone Mechanism Behind Mounjaro
Mounjaro's unique approach to weight loss involves activating two hormone receptors simultaneously: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). These are natural hormones your body produces after eating that help regulate hunger and blood sugar. When you use Mounjaro, these signals are amplified, which means your brain receives stronger "fullness" signals earlier during meals. This can help you eat less without feeling deprived.
The medication also slows gastric emptying—the rate at which food moves from your stomach into the intestines. This effect helps you feel satisfied for longer after eating, reducing the urge to snack between meals. Over time, this can lead to a sustainable calorie deficit. Additionally, Mounjaro may help your body better utilise fat stores for energy, supporting the weight loss process. Each person responds differently, so results vary significantly between individuals.
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.
Clinical Evidence and Expected Weight Loss Results
The SURMOUNT-1 clinical trial, the largest study of tirzepatide for weight management, followed over 2,500 adults for 72 weeks. Participants using the maximum dose (15 mg) alongside lifestyle changes lost an average of approximately 20.9% of their body weight. Lower doses showed proportionally less weight loss—around 15% at the 5 mg dose. However, these are averages; some people lost significantly more, while others experienced more modest results. Weight loss typically continues to improve as your dose increases over the first 4–5 months, then stabilises. Your GP or prescriber can discuss what to expect based on your individual circumstances and health history.
- 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 long does it take to see weight loss results with Mounjaro?
Most people begin noticing appetite changes within 1–2 weeks of starting. Visible weight loss typically appears within 4–6 weeks, but significant results develop over 3–6 months as your dose increases and your body adjusts. Everyone's timeline differs. Use our free GLP-1 weight loss calculator to project potential results.
Is Mounjaro the same as Wegovy for weight loss?
No. Both are prescription weight loss injections, but Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1), whilst Wegovy (semaglutide) activates only GLP-1. Clinical trials show Mounjaro may produce slightly higher average weight loss, but individual results vary. Your prescriber will recommend which suits you best.
Does Mounjaro work without diet and exercise changes?
Mounjaro is most effective when combined with a reduced-calorie diet and increased physical activity—this is how clinical trials were conducted. The medication supports these efforts by reducing hunger and cravings, but it works best as part of a comprehensive approach to weight management, not as a standalone solution.
What is the starting dose of Mounjaro, and how does it increase?
The starting dose is 2.5 mg once weekly. Your prescriber increases your dose by 2.5 mg every 4 weeks, up to a maximum of 15 mg weekly. This gradual dose titration helps your body adjust and reduces side effects. You'll stay on your current dose for at least 4 weeks before increasing.
Can you use Mounjaro long-term for weight management?
Yes, Mounjaro can be used long-term if it continues to help you and your prescriber agrees it's safe. Many people maintain their weight loss by continuing the medication. However, stopping Mounjaro may result in weight regain. Your GP will monitor you regularly to ensure it remains appropriate for your health.
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.