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 Weight Loss Injections Work in UK Pharmacies
Weight loss injections available through UK pharmacies are prescription-only medications that work by mimicking natural hormones to reduce appetite and support weight management. The most commonly prescribed options are Wegovy (semaglutide) and Mounjaro (tirzepatide), both approved for weight loss in UK adults. These medications require a clinical assessment from a licensed prescriber before you can access them, whether through the NHS or privately. They're typically used alongside diet and exercise changes, not instead of them. Our GLP-1 weight loss calculator can help you understand potential weight loss at different doses.
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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.
What Pharmacy Weight Loss Injections Are
Pharmacy weight loss injections are prescription-only GLP-1 and GIP/GLP-1 receptor agonist medications that work by activating natural hormone pathways in your body. These injections help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. In the UK, the two main licensed options are Wegovy (semaglutide), which activates GLP-1 receptors, and Mounjaro (tirzepatide), which activates both GIP and GLP-1 receptors for a dual mechanism.
Unlike cosmetic injections, these are prescription medicines requiring clinical assessment. They're administered once weekly as self-injection pens that you store at home. Clinical trials have shown that individuals using these medications alongside reduced-calorie diets and increased physical activity may achieve weight loss averaging 15–21% of body weight, though individual results vary significantly.
Important: Ozempic also contains semaglutide but is licensed for type 2 diabetes, not weight loss in the UK — Wegovy is the licensed weight management version of semaglutide.
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.
Pharmacy Access and Eligibility
In the UK, weight loss injections are available through two main routes: NHS specialist services and private prescription through GPhC-registered pharmacies. NHS access typically requires referral to a tier 3 weight management service through your GP, though availability varies significantly by region and waiting times can be lengthy.
Private access is faster — you can have an online consultation with a UK-licensed prescriber, and if deemed clinically appropriate, your prescription is dispensed by a registered pharmacy. You're eligible if you have a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Prescribers may recommend lower thresholds for people of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher health risks at lower BMI levels. Check your BMI using our free BMI calculator above.
Costs, Storage, and SafetyPrivate pharmacy costs typically range from £129 to £320 per month depending on the dose and provider — significantly higher than NHS provision if available to you. Storage is critical: unopened pens must be refrigerated at 2–8°C and kept in their original carton. Once started, pens can be stored at room temperature (below 30°C) for up to 30 days before disposal.
The most common side effects are nausea, diarrhoea, constipation, and stomach pain — these often reduce as your body adjusts. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and allergic reactions. You must inform your prescriber of all medications because weight loss injections may reduce absorption of oral contraceptives and some other drugs. Always rotate injection sites between stomach, thigh, and upper arm to prevent irritation. Track your progress with our free progress tracker to monitor changes alongside any medication use.
- 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.
Are weight loss injections available on the NHS?
Yes, but access is limited. Tirzepatide (Mounjaro) and semaglutide (Wegovy) are approved for NHS specialist weight management services, typically accessed through tier 3 services via GP referral. However, availability varies significantly by region and waiting lists can be very long. Private access through GPhC-registered pharmacies is faster and doesn't require NHS referral.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (doses up to 2 mg) and is NOT licensed for weight loss in the UK. Wegovy is specifically approved for weight management (dose 2.4 mg) and is the correct option if weight loss is the goal. Using Ozempic for weight loss is off-label in the UK.
How quickly will I lose weight on these injections?
Clinical trials show average weight loss of 15–21% of body weight over several months alongside diet and exercise changes. However, individual results vary significantly — some people lose more, some less. Weight loss typically becomes noticeable over weeks 8–12 as you reach higher doses. Your GP can give you personalised expectations.
Can I use weight loss injections if I'm taking other medications?
Most medications are compatible, but some interactions exist — particularly with oral contraceptives and certain diabetes medications. Weight loss injections may reduce oral medication absorption, so inform your prescriber of all medications. They'll assess whether it's safe for you and whether any dose adjustments are needed.
What happens if I stop taking weight loss injections?
Weight loss injections are typically used for ongoing weight management rather than as a short course. If you stop, appetite regulation returns to baseline and weight can increase again. This is why they're used alongside permanent lifestyle changes. Your prescriber will discuss long-term plans and whether continuing treatment is appropriate for you.
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.