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 Is 2.5 Mounjaro — Starting Dose Explained
2.5 mg is the starting dose of Mounjaro (tirzepatide) when you first begin treatment. This is a prescription-only, once-weekly injection licensed in the UK for weight management in adults with a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions. The 2.5 mg dose is not intended as a long-term maintenance dose — it's a four-week adjustment period to help your body adapt to the medication. Your prescriber will typically increase your dose after this initial phase. Understanding what this dose is for helps you know what to expect from your treatment journey.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 2.5 mg Works in Your Body
Mounjaro is a dual GIP and GLP-1 receptor agonist, which means it activates two natural hormone pathways that regulate appetite and blood sugar. At the 2.5 mg starting dose, these effects are gentler than at higher doses, allowing your body to adjust gradually.
- May help reduce appetite and food cravings
- Supports feeling fuller after smaller meals
- Slows how quickly food leaves your stomach
- Helps regulate how your body uses fat
This is why 2.5 mg is given first — it's a lower dose that allows your system to adapt before escalating. Unlike the Mounjaro KwikPen doses that follow (5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg), the 2.5 mg dose is a transition phase rather than a maintenance dose. Most people stay on 2.5 mg for exactly 4 weeks before moving to the next dose, assuming no significant side effects.
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.
What to Expect on Mounjaro 2.5 mg
When you inject your first 2.5 mg Mounjaro dose, you may notice some effects within a few days, though not everyone experiences changes immediately. Common experiences at this dose include mild nausea, reduced appetite, or changes in digestion — these often settle as your body adjusts.
Weight loss at 2.5 mg is usually modest compared to higher doses, as this is the adjustment phase. Clinical trials focused on the full treatment course at higher doses (like 15 mg), so specific weight loss data for 2.5 mg alone is limited. The NHS and private prescribers use this dose as a safety step — if side effects are manageable after 4 weeks, you'll typically progress to 5 mg and beyond.
- 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 enough for weight loss?
Not typically — 2.5 mg is the starting adjustment dose, not a treatment dose. It's designed to let your body adapt over 4 weeks before increasing. Most weight loss occurs at higher doses (5 mg and above). This dose alone is unlikely to produce significant results, but it's an important safety phase.
How long do you stay on 2.5 mg Mounjaro?
Exactly 4 weeks. You inject 2.5 mg once weekly for 4 weeks (4 injections total), then your prescriber will increase your dose to 5 mg for the next 4 weeks, assuming side effects are manageable. This titration schedule continues until you reach your target maintenance dose.
What side effects are common at 2.5 mg?
The most common side effects at any Mounjaro dose — including 2.5 mg — are nausea, diarrhoea, constipation, and stomach pain. At the starting dose, these tend to be milder than at higher doses. Most side effects settle within days or weeks as your body adjusts. Contact your prescriber if side effects are severe or persistent.
Is Mounjaro the same as Wegovy at 2.5 mg?
No. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1-only agonist. They're different medications with different mechanisms — you cannot compare Mounjaro doses directly to Wegovy doses. Both require a UK prescription and clinical assessment before starting.
Can I get Mounjaro 2.5 mg on the NHS?
Mounjaro is available through NHS tier 3 specialist weight management services, but availability varies significantly by region and waiting lists can be long. Private online prescribers can also assess and prescribe Mounjaro. Either route requires a clinical assessment to confirm you meet eligibility criteria (BMI ≥30 or ≥27 with weight-related health conditions).
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.