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 Are the Side Effects of gradual weight management?
Losing weight quickly can cause unwanted side effects, even when using prescription weight loss medication. While weight loss injections like Wegovy (semaglutide) can help with weight management in the UK, gradual weight management — whether through diet, exercise, or medication — may cause nausea, fatigue, hair loss, gallstones, and nutrient deficiencies. The NHS recommends losing no more than 0.5–1 kg per week for sustainable, safer results. Understanding potential side effects helps you make informed decisions about your weight loss journey and know when to contact your GP.
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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.
Common Side Effects of gradual weight management
gradual weight management can trigger several side effects as your body adjusts to significant changes. Gastrointestinal issues are most common — nausea, diarrhoea, constipation, and stomach pain affect many people losing weight quickly. These often improve after a few weeks but can be uncomfortable initially.
Fatigue and weakness occur because your body is losing energy stores rapidly. Hair loss (alopecia) may develop weeks after starting weight loss, especially if calorie restriction is severe. Dizziness and headaches can result from dehydration or electrolyte imbalances.
More serious side effects include gallstones, which develop in 10–25% of people losing more than 1.5 kg per week over several months. Nutrient deficiencies — particularly vitamin B12, iron, calcium, and protein — are risks with very gradual weight management. Your GP can monitor your health and recommend supplements if needed.
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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 Prescription Weight Loss Medication Affects gradual weight management
In the UK, prescription weight loss injections like Wegovy (semaglutide) are GLP-1 receptor agonist medications that may help achieve weight loss when used with diet and physical activity. Clinical trials (STEP programme) showed participants lost an average of approximately 15% of body weight — though individual results vary significantly.
These medications cause their own side effects: nausea, vomiting, constipation, and indigestion are very common, especially when starting or increasing doses. However, weight loss medication is prescription-only and used under clinical supervision, which helps manage side effects. The NHS recommends losing weight at 0.5–1 kg per week even with medication. Always discuss side effects with your GP or prescriber — they can adjust your approach or offer support.
- 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 gradual weight management ever safe?
The NHS recommends losing 0.5–1 kg per week as the safe, sustainable rate. Faster loss increases risks of muscle loss, nutritional deficiencies, gallstones, and metabolic damage. Only under medical supervision (such as with prescription weight loss medication or a low-calorie diet programme) should faster loss be considered, and only with regular monitoring.
Can weight loss injections cause gradual weight management side effects?
Yes. Wegovy and Mounjaro are prescription-only weight loss injections that may cause nausea, vomiting, constipation, and fatigue — especially as doses increase. These are usually temporary and improve within weeks. However, if you experience severe stomach pain, gallbladder symptoms, or persistent vomiting, contact your GP immediately.
How long do gradual weight management side effects last?
Gastrointestinal side effects (nausea, diarrhoea) typically improve within 2–4 weeks as your body adapts. Fatigue and headaches usually resolve within 1–2 weeks once hydration and electrolyte balance stabilise. Hair loss may persist for several months if weight loss continues rapidly. Always inform your GP if side effects don't improve.
What nutrient deficiencies happen with gradual weight management?
gradual weight management increases risks of vitamin B12, iron, calcium, and protein deficiencies — especially if calorie intake is very low. Your GP can check your nutrient levels with blood tests and recommend supplements. Eating protein at every meal and choosing nutrient-dense foods helps prevent deficiencies.
Should I use a weight loss calculator to track my progress safely?
Yes. MyWeightCheck's free GLP-1 weight loss calculator and progress tracker help you estimate realistic weight loss and monitor your journey at a healthy pace. Combined with your BMI calculator, these tools support safe, sustainable weight loss aligned with NHS guidance — aiming for 0.5–1 kg per week rather than rapid loss.
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.