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 Does mg Mean in Medication and Health?
Mg stands for milligram — a unit of measurement used to describe the dose of medications and health supplements. One milligram equals one-thousandth of a gram (0.001g). In UK health guidance and NHS prescriptions, mg is the standard unit for measuring medicine doses. Whether you're taking prescription weight management injections like Wegovy or Mounjaro, or any other medication, the dose will always be expressed in milligrams. Understanding what mg means helps you take medications safely and follow your healthcare provider's instructions correctly.
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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 Milligrams Work in Medication Dosing
Milligrams (mg) are used across all UK healthcare to standardise medication doses. One milligram is an extremely small amount — to put it in perspective, a single grain of salt weighs roughly 40mg. Medications are prescribed in specific mg amounts because the dose must be precise to be safe and effective.
Common medication doses in the UK include:
- Wegovy (semaglutide) for weight management: doses from 0.25mg up to 2.4mg once weekly
- Mounjaro (tirzepatide) for weight management: doses from 2.5mg up to 15mg once weekly
- Standard paracetamol tablets: typically 500mg per tablet
- Standard ibuprofen: typically 200mg or 400mg per tablet
Your prescriber will specify exactly how many mg you need based on your health condition, body weight, and how your body responds to the medication. NHS guidance always expresses prescription doses in milligrams to ensure consistency and patient safety across the UK healthcare system.
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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.
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Understanding Your Prescription Dose in Milligrams
When you receive a prescription from your GP or a licensed prescriber, the dose will be clearly stated in mg. For injectable medications like weight management injections, the mg amount tells you exactly how much active ingredient is in each pen or injection. For example, if you're prescribed Wegovy, your prescriber might start you on 0.25mg and gradually increase the dose every four weeks — moving through 0.5mg, 1mg, 1.7mg, and up to the maximum of 2.4mg.
Understanding your mg dose matters because it helps you recognise if you've been given the correct medication at the correct strength. Always check that the mg amount on your prescription matches what you've been dispensed. If you're unsure about your dose or how to use it, contact your prescriber or pharmacist — they can explain your specific mg dose and answer any questions about why that particular dose has been chosen for you.
- 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 many milligrams are in a gram?
One gram equals 1,000 milligrams (mg). So 1mg is one-thousandth of a gram. This is why medication doses are expressed in milligrams — it allows for very precise and safe dosing. For example, Wegovy doses start at just 0.25mg per injection.
Why do UK medications use mg instead of other measurements?
Milligrams provide precision and consistency across the NHS and all UK healthcare. Using a standardised unit in milligrams ensures that every patient receiving the same prescription gets exactly the same dose, reducing risk of error and improving safety and effectiveness.
What does it mean if my weight loss injection dose increases from 5mg to 10mg?
An increase from 5mg to 10mg means you're moving to a higher dose of the active ingredient. For medications like Mounjaro, doses are gradually increased every 4 weeks to help your body adjust and to find the most effective dose for you. Your prescriber will monitor how you respond.
Is a higher mg dose always more effective for weight loss?
Not necessarily — individual results vary significantly. Clinical trials show that higher doses may help some people achieve greater weight loss, but the most effective dose depends on your personal response, health conditions, and tolerance. Your prescriber will personalise your dose based on your needs.
Can I adjust my mg dose myself?
No — never adjust your medication dose without speaking to your prescriber first. Changing your dose without guidance could be unsafe. Always contact your GP or the prescriber who issued your prescription if you want to discuss your dose, experience side effects, or have concerns about your medication.
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