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
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What Is 2.5 Mg Mounjaro In Units?
2.5 mg is the starting dose of Mounjaro (tirzepatide), the prescription-only weight management injection available in the UK. This is the lowest dose you'll receive when beginning treatment, typically used for the first four weeks before increasing to maintenance doses. Understanding your dose and how it fits into the full treatment pathway can help you know what to expect from your Mounjaro prescription. Use our GLP-1 weight loss calculator to explore projected results across different dose levels.
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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.
Understanding Mounjaro 2.5 Mg As A Starting Dose
2.5 mg is Mounjaro's starting or "dose escalation" dose, designed to allow your body to adjust to the medication and minimise nausea and gastrointestinal side effects. You'll stay on 2.5 mg for a minimum of four weeks before your prescriber considers increasing to the next dose level. The full dose escalation pathway for tirzepatide is: 2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg (maximum). Each step is a once-weekly injection. Your prescriber will assess your response and tolerability before moving to the next dose. Not everyone reaches 15 mg—some people achieve their weight loss goals at 5 mg or 10 mg and may maintain at that level. Starting low allows time to adjust to common side effects like nausea and diarrhoea, which often reduce as your body adapts.
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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.
How 2.5 Mg Compares To Other Doses And Effectiveness
Clinical trial data showed that higher Mounjaro doses produced greater average weight loss: 5 mg achieved approximately clinically studied weight loss, 10 mg achieved 19.5%, and 15 mg achieved 20.9%. However, 2.5 mg is a starting dose only—it's not designed for long-term use or as a maintenance dose. Most people remain on 2.5 mg for just four weeks before escalating. Individual results vary widely based on diet, physical activity, metabolism, and personal response. Your prescriber may adjust your escalation schedule based on side effects or your progress. Remember that Mounjaro vs Wegovy (semaglutide) shows different mechanisms: Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is GLP-1 only—both require prescription and clinical assessment in the UK.
- 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 2.5 mg Mounjaro an effective weight loss dose?
2.5 mg is a starting dose, not designed for long-term weight loss. It allows your body to adapt to the medication. Most people escalate to higher doses (5 mg or above) for weight loss benefits. Clinical trials showed meaningful results at 5 mg and above.
How long do you stay on 2.5 mg Mounjaro?
You'll remain on 2.5 mg for a minimum of four weeks, then your prescriber will assess whether to increase to 5 mg. The timing depends on your tolerability, side effects, and response. Never increase the dose without guidance from your prescriber.
What are the side effects of 2.5 mg Mounjaro?
Common side effects include nausea, diarrhoea, constipation, and stomach discomfort. These often reduce as your body adjusts. Starting at 2.5 mg helps minimise these effects. Serious side effects are rare but require immediate medical attention, such as severe abdominal pain.
Can you buy 2.5 mg Mounjaro on the NHS in the UK?
Mounjaro is available on the NHS through specialist tier 3 weight management services, though regional availability and waiting lists vary significantly. Private prescriptions are available through online clinical assessments. Always discuss options with your GP first.
How does 2.5 mg Mounjaro dosing differ from Wegovy?
Mounjaro starts at 2.5 mg, while Wegovy (semaglutide) starts at 0.25 mg—a much lower starting dose. Mounjaro's dose escalation pathway is also different, and it's a dual GIP/GLP-1 agonist versus Wegovy's single GLP-1 mechanism. Both require prescription in the UK.
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.