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 Do Mounjaro Studies Show?
Mounjaro (tirzepatide) is backed by several clinical trials that demonstrate its effectiveness for weight management in adults. The most significant UK-relevant study is the SURMOUNT-1 trial, which showed that tirzepatide helped participants achieve meaningful weight loss alongside diet and exercise changes. Understanding what these studies reveal helps you and your GP make informed decisions about whether this prescription-only medication might be suitable for you. The evidence forms the basis for Mounjaro's approval in the UK and its use within NHS specialist weight management services.
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.
Key Findings from the SURMOUNT-1 Trial
The SURMOUNT-1 trial was the pivotal clinical study that led to Mounjaro's approval for weight management. Over 72 weeks, participants taking the maximum dose of 15 mg achieved an average weight loss of approximately 20.9% of their body weight, compared to around 3.3% in the placebo group. At the 10 mg dose, average weight loss was approximately 19.5%. The 5 mg dose produced approximately 15% average weight loss. These results were achieved alongside a reduced-calorie diet and increased physical activity — the medication alone did not cause weight loss without lifestyle changes.
- Participants also experienced improvements in blood sugar control and cardiovascular risk markers
- Results varied significantly between individuals — some lost more, some less
- The dual GIP and GLP-1 mechanism of tirzepatide appeared more effective than single GLP-1 agonists in trial conditions
- Side effects were common but mostly manageable, with nausea and gastrointestinal symptoms most frequently reported
Important context: These are clinical trial averages. Your GP can discuss what realistic weight loss might look like for you personally, as individual responses vary considerably based on genetics, adherence, diet quality, and exercise consistency.
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.
How Mounjaro Studies Inform UK Clinical Practice
SURMOUNT trial data directly influenced MHRA approval and NICE guidance for tirzepatide in the UK. Specialist weight management services now prescribe Mounjaro based on this evidence, using the dose titration schedule proven effective in trials — starting at 2.5 mg and escalating weekly by 2.5 mg increments up to the maximum 15 mg. NHS services use these studies to assess eligibility: adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or hypertension, may be considered.
- Trial data showed the mounjaro kwikpen delivery system was effective and well-tolerated
- Studies confirm the importance of mounjaro dose titration — gradual increases reduce side effects
- Evidence supports using Mounjaro alongside comprehensive lifestyle support, not as a standalone solution
You can calculate your potential weight loss range using our free GLP-1 weight loss calculator, though individual results will differ from trial averages. Your GP can provide personalised guidance based on your specific health profile.
- 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 were the Mounjaro studies?
The primary SURMOUNT-1 trial ran for 72 weeks (approximately 17 months) of treatment. Participants were then followed for an additional period to monitor weight regain after stopping medication. This timeframe provided robust evidence of both short-term and longer-term effects, informing how NHS services prescribe and monitor the medication.
Did all study participants lose weight on Mounjaro?
No. While average weight loss was significant, individual responses varied considerably. Some participants achieved greater weight loss than the average, while others achieved less. This variation reflects real-world use — your personal results depend on genetics, diet adherence, activity level, and individual metabolism. Your GP can discuss realistic expectations for you.
How do Mounjaro studies compare to Wegovy studies?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are supported by clinical trials. Mounjaro showed slightly higher average weight loss (20.9% at maximum dose) compared to Wegovy's average of approximately 14.9%. However, both are effective, and mounjaro vs wegovy choice depends on individual factors assessed during clinical consultation with your prescriber.
Can I rely on SURMOUNT trial results to predict my weight loss?
SURMOUNT results show what is possible on average, but individual outcomes vary significantly. Trial participants followed structured reduced-calorie diets and exercise plans under supervision — your real-world results will depend on your personal adherence to lifestyle changes. Your GP or prescriber can give more personalised projections based on your circumstances.
What do UK studies say about Mounjaro safety?
SURMOUNT trial data and post-approval monitoring through UK pharmacovigilance show Mounjaro is generally well-tolerated. The most common side effects are nausea, vomiting, and diarrhoea — usually mild to moderate and often reduce over time. Serious side effects are rare but possible. Your GP will assess risks versus benefits during mounjaro eligibility uk evaluation before prescribing.
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.