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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Fibromyalgia and Mounjaro: A UK Health Guide
If you have fibromyalgia and are considering weight management options, it's important to understand how prescription medications like Mounjaro work and whether they might be suitable for you. Fibromyalgia often makes weight management more challenging due to pain, fatigue, and reduced mobility. This guide explores Mounjaro, weight management, and how to discuss these options with your GP, who can assess your individual health needs and any potential interactions with your condition.
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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.
How Mounjaro Works and Fibromyalgia Considerations
Mounjaro (tirzepatide) is a prescription-only injection licensed in the UK for weight management in adults. It works by activating two natural hormone pathways — GIP and GLP-1 — to help regulate appetite and support feeling fuller after smaller meals. The dual GIP + GLP-1 mechanism differs from single GLP-1 medications like Wegovy (semaglutide), which activate only the GLP-1 pathway.
For people with fibromyalgia, weight management can be beneficial because excess weight places additional strain on joints and muscles, potentially worsening pain and fatigue. However, fibromyalgia can make traditional weight loss approaches difficult — pain and fatigue may limit physical activity, and some people experience medication interactions or side effects that complicate treatment. This is why clinical assessment is essential. Your GP or prescriber will evaluate whether Mounjaro is safe for you, considering your fibromyalgia symptoms, current medications, and overall health.
Mounjaro is delivered via a Mounjaro KwikPen — a pre-filled weekly injection that you self-administer. The Mounjaro dose titration process starts at 2.5 mg, gradually increasing over weeks to allow your body to adjust.
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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.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
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Mounjaro vs Wegovy: Comparison for Fibromyalgia
Both Mounjaro and Wegovy are prescription-only weight management medications, but they work differently. Mounjaro (tirzepatide) uses dual GIP + GLP-1 activation, while Wegovy (semaglutide) activates GLP-1 only. Clinical trials showed Mounjaro users lost an average of 15–21% of body weight, whilst Wegovy users lost approximately 15% — though individual results vary significantly.
For fibromyalgia specifically, the choice between them is not about which is "better" for pain management, as neither medication directly treats fibromyalgia. Instead, it depends on which is most suitable after clinical assessment. Common side effects for both include nausea, constipation, and reduced appetite — side effects that may interact with fibromyalgia symptoms or existing pain medications. Your prescriber will consider Mounjaro UK prescription eligibility, your medical history, and whether Mounjaro vs Wegovy aligns better with your individual circumstances.
Access to Mounjaro through the NHS depends on specialist tier 3 weight management services and varies significantly by region. Private prescription is available through online assessment. Regardless of route, a licensed prescriber must assess whether weight management medication is appropriate for you, especially with fibromyalgia. They will review your current medications (some pain medications can interact with GLP-1 treatments), fibromyalgia symptoms, and any contraindications.
The decision should always be made together with your GP or specialist. Weight management is one part of a broader fibromyalgia management plan that might include pain management, physiotherapy, pacing strategies, and psychological support. Use our free BMI calculator above to check your starting point, and our GLP-1 weight loss calculator to explore potential outcomes if medication is prescribed following clinical assessment.
- 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.
Can I take Mounjaro if I have fibromyalgia?
Mounjaro may be suitable, but requires individual clinical assessment by your GP or prescriber. They will consider your fibromyalgia symptoms, current pain medications, and overall health to determine safety and suitability. Some pain medications may interact with GLP-1 treatments, so disclosure of all medications is essential.
Will Mounjaro help with fibromyalgia pain?
Mounjaro is not a fibromyalgia treatment — it does not directly relieve pain or fatigue. However, weight management may reduce additional strain on joints and muscles, which could indirectly help some fibromyalgia symptoms. Weight loss is a supportive measure alongside proper fibromyalgia management.
What's the difference between Mounjaro and Wegovy for fibromyalgia?
Mounjaro uses dual GIP + GLP-1 activation; Wegovy uses GLP-1 only. Clinical trials showed different average weight loss outcomes, but both require the same clinical assessment. For fibromyalgia, the choice depends on which medication your prescriber considers safest for you individually — neither treats fibromyalgia directly.
Are there side effects I should know about with fibromyalgia?
Common Mounjaro side effects include nausea, constipation, and reduced appetite. With fibromyalgia, these may interact with existing pain, fatigue, or current medications. Your prescriber must assess these risks before prescription. Always report all fibromyalgia symptoms and medications during assessment.
How do I access Mounjaro in the UK with fibromyalgia?
NHS access is through tier 3 specialist weight management services via GP referral; availability varies by region. Private prescription requires online clinical assessment by a UK-licensed prescriber. Either route requires assessment of your fibromyalgia, current treatments, and suitability for GLP-1 medication.
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