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
Understanding Mounjaro Low Dose Treatment
Mounjaro treatment in the UK starts with a low dose of 2.5mg for your first four weeks. This initial dose is a starting or adjustment phase designed to help your body adapt to the medication while your prescriber monitors how you respond. The 2.5mg KwikPen is not a maintenance dose — it's the foundation of a carefully structured dose titration plan that typically increases every 4 weeks until you reach an effective maintenance dose. Understanding how this low dose works and what comes next is essential for managing expectations and getting the most from this weight management treatment.
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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.
How Mounjaro Low Dose Works
The 2.5mg Mounjaro dose activates GIP and GLP-1 receptor pathways in your body, mimicking natural hormones that help regulate appetite and food intake. Even at this low starting dose, many people notice changes in how food tastes or feels satisfying, though the full effects typically develop as your dose increases.
At the 2.5mg dose, you may experience some nausea or digestive changes — this is common and often improves within 1–2 weeks as your body adjusts. Your prescriber will assess your response at the end of week 4 before deciding whether to progress to the next dose. If you're managing well and tolerating the injection, you'll typically move to 5mg in week 5. The tirzepatide dose escalation follows this structured pathway: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg, with a minimum of 4 weeks at each dose.
Each KwikPen contains 4 pre-filled doses of the same strength, so your 2.5mg pen will last exactly 4 weeks if you inject once weekly on your scheduled day.
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.
Starting Low Dose — What to Expect
In your first week on Mounjaro 2.5mg, nausea is the most commonly reported side effect — it may feel similar to mild travel sickness and often peaks in days 2–3 before settling. Eating smaller, less fatty meals can help. Some people also notice constipation or mild stomach discomfort; staying hydrated and gradually increasing fibre can support this.
Your injection technique is the same regardless of dose: subcutaneous injection into your stomach, upper thigh, or upper arm, once weekly on the same day. Store unopened pens in the fridge (2–8°C) and use our GLP-1 weight loss calculator to estimate your potential progress as your dose increases over the coming months. Most people remain on low doses for only 4 weeks before progressing, so don't assume 2.5mg is your long-term dose.
- 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 2.5mg Mounjaro enough to lose weight?
At 2.5mg, weight loss may be modest compared to higher doses. Clinical data shows most significant weight loss occurs at maintenance doses (10mg–15mg). The 2.5mg dose is primarily for tolerance assessment, not the therapeutic dose. Expect progression to higher doses within weeks.
How long do I stay on 2.5mg Mounjaro?
Typically 4 weeks. After week 4, if you're tolerating the injection well, your prescriber will usually recommend increasing to 5mg in week 5. Some people may stay longer if side effects are significant, but the standard pathway is monthly dose increases.
Can I skip doses or stay on low dose longer?
Only your prescriber can make this decision. If you're experiencing significant side effects, discuss this with them — dose progression can sometimes be slowed. Never skip doses without guidance, as this disrupts your treatment schedule and may affect results.
What's the difference between Mounjaro 2.5mg and Wegovy low dose?
Mounjaro starts at 2.5mg (tirzepatide, dual GIP+GLP-1), while Wegovy starts at 0.25mg (semaglutide, GLP-1 only). Mounjaro's starting dose is higher because its dual mechanism differs. Both follow dose titration plans, but the schedules and maximum doses differ.
Should I use my BMI calculator before starting Mounjaro?
Yes. Calculate your current BMI using our free BMI calculator to establish your baseline. This helps you track meaningful progress as your dose increases, and gives your prescriber context for eligibility assessment and expected outcomes.
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.