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
Mounjaro and Amitriptyline — What You Need to Know
If you're taking amitriptyline and considering Mounjaro (tirzepatide), it's important to understand how these medications interact. Mounjaro is a prescription-only GLP-1 and GIP receptor agonist used for weight management in UK adults, whilst amitriptyline is a tricyclic antidepressant. Both can affect digestion and appetite, so medical guidance is essential before combining them. Always inform your prescriber of all medications you're currently taking, including amitriptyline, before starting Mounjaro or any weight loss injection.
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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.
How Mounjaro and Amitriptyline Affect Your Body
Mounjaro works by activating GIP and GLP-1 receptors, which regulate appetite, blood sugar, and how quickly food moves through your digestive system. Amitriptyline, commonly prescribed for depression, nerve pain, and migraines, can slow gastric emptying and affect appetite as side effects. When combined, these effects may be amplified, potentially causing increased nausea, constipation, or reduced appetite beyond what either medication alone would cause.
Additionally, amitriptyline can affect how some oral medications are absorbed in the stomach. Since Mounjaro may also slow gastric transit, a healthcare prescriber needs to assess whether this combination is safe for you individually. The KwikPen injection itself bypasses the stomach, but the overall digestive effects require careful monitoring.
Your GP or prescriber should review your full medication history—including the dose of amitriptyline you're taking and how long you've been on it—before approving Mounjaro treatment.
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.
NHS Guidance and Private Prescription Safety
NHS route: If you're under NHS specialist weight management services, your prescriber will have access to your full medical records, including amitriptyline use. They can assess the interaction risk and monitor you during dose titration. This is the safest route if available in your area.
Private route: When using an online prescriber for a private Mounjaro prescription, you must declare all medications, including amitriptyline, during your clinical consultation. A responsible UK-licensed prescriber will ask detailed questions about your current medications and may request you to discuss the combination with your GP before proceeding. Never withhold medication information during a consultation.
Before starting Mounjaro, use our free BMI calculator to understand your baseline, and discuss the full picture with your healthcare provider.
- 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'm already on amitriptyline?
Potentially yes, but only with medical approval. Both medications can affect digestion and appetite. Your prescriber must review your amitriptyline dose, duration, and reason for use before approving Mounjaro. You should never start Mounjaro without informing your prescriber that you take amitriptyline. Always declare all medications during any clinical assessment.
Will amitriptyline and Mounjaro cause severe side effects together?
The combination may increase nausea, constipation, and reduced appetite compared to either medication alone. This doesn't automatically make it unsafe—your prescriber assesses individual risk. Monitoring is essential during the first weeks and during dose titration. Report any unusual symptoms to your GP immediately.
Should I stop amitriptyline before starting Mounjaro?
No—never stop amitriptyline without your GP's guidance. Stopping antidepressants abruptly can cause withdrawal symptoms and mood complications. Discuss with your GP whether to continue, adjust the dose, or switch to an alternative antidepressant before starting Mounjaro. Your prescriber and GP should communicate about this.
Can amitriptyline reduce how well Mounjaro works?
Amitriptyline doesn't directly reduce Mounjaro's weight loss effects. However, because amitriptyline can increase appetite as a side effect in some people, it may offset some of Mounjaro's appetite-suppressing benefits. Your prescriber will discuss this during your consultation and may adjust your amitriptyline dose if needed.
What if I'm prescribed Mounjaro and my GP wants to change my amitriptyline?
Inform your Mounjaro prescriber immediately if your GP suggests changing amitriptyline. Both prescribers need to know about any changes. Your GP may switch you to a different antidepressant with fewer digestive side effects. Mounjaro dose titration takes several weeks, so timing of medication changes is important for safety.
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.