What You Should Know About Weekly Weight Loss Injections
Mounjaro and Wegovy are both prescription-only, once-weekly injectable medicines. Mounjaro's active substance is tirzepatide, a dual GIP and GLP-1 receptor agonist. Wegovy's active substance is semaglutide, a GLP-1 receptor agonist. Both work on appetite-regulating pathways in the brain and slow gastric emptying, which many people experience as a reduced sense of hunger and less preoccupation with food — sometimes called reduced "food noise".
How they are taken
Both medicines are supplied as pre-filled injection pens and are injected once a week, typically into the abdomen, outer thigh, or upper arm. Your prescriber or doctor will advise on the dose schedule that is right for you — dose adjustments are always a clinical decision, not something to change on your own. For factual prescribing information, the electronic Medicines Compendium (eMC) holds the full patient information leaflets for both products.
Injection site rotation
Rotating injection sites is widely recommended to reduce the risk of skin reactions such as lipohypertrophy (thickening or hardening under the skin). Common practice is to move around within and between sites — for example, using different areas of the abdomen across consecutive weeks — rather than repeatedly injecting in the same spot. Your prescriber or the patient information leaflet that came with your pen is the right place to get guidance specific to your medicine.
Commonly reported side effects
Gastrointestinal effects — nausea, constipation, diarrhoea, indigestion — are the most commonly reported side effects, particularly when starting or after a dose increase. Many people find these ease over time. If side effects are severe, persistent, or worrying, contact your healthcare professional promptly. Both medicines carry a black triangle (▼) status, meaning they are subject to additional monitoring; any suspected side effects should be reported to your healthcare professional and to your national reporting scheme (such as the UK's Yellow Card scheme).
For a broader look at how these medicines compare, see our guide to weight loss injections. If you are on Wegovy specifically, our Wegovy injections overview covers what to expect in more detail.
average weekly weight change in the first 16 weeks of Mounjaro & Wegovy use*
Tracking the right four numbers — weight, waist, protein and dose — turns a noisy chart into a clear story. That's the loop GLP-1 users keep coming back for.
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How GLP Trackr Helps You Stay on Top of Your Injections
Keeping track of injection sites across a weekly schedule is easy to lose sight of — especially as you move through different dose stages. GLP Trackr's injection-site tracking feature logs each site you use and automatically suggests your next rotation, so you never have to rely on memory. Over time you build a clear rotation history that you can review or share with your prescriber.
Alongside site tracking, the app logs every dose — the date, time, and strength — and sends a gentle reminder so a weekly injection is never accidentally missed. Many people find that having a reliable record of their injection history helps them feel more in control of their routine, and gives them something concrete to refer back to during prescriber appointments.
GLP Trackr also lets you log side effects and spot patterns over time — useful context to bring to any clinical review. If you are curious about cost considerations around these medicines, our page on Mounjaro injection pricing covers what to be aware of. You can also explore more about weight loss injections in our related content.
Any decision about your dose or injection schedule should always be made with your prescriber — GLP Trackr helps you record and organise your journey, but it is not a substitute for their guidance.
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Morning Check-In
Start every day with a 60-second wellness check-in. Log how you're feeling, track nausea, appetite, energy, and mood — giving you and your care team a complete picture of how your medication is working.
Injection Tracking
Log every dose with a single tap. Track your dose history, phase in your cycle, estimated medication levels, and upcoming injection dates — with reminders so you never miss a scheduled shot.
Hydration Reminders
Staying hydrated is especially important on GLP-1 medications. Set daily water targets, log intake throughout the day, and receive smart nudges when you're falling behind your goal.
Smart Meal Planning
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Progress Analytics
Beautiful, easy-to-read charts show your weight loss trajectory, weekly nutrition trends, medication responses, and wellbeing scores over time — turning raw data into genuine insights.
AI Meal Scanning
Snap a photo of any meal and get a full nutrition breakdown in seconds — calories, protein, carbs, fat, and fibre. No searching. No manual logging. Just point, snap, and track.
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Log walks, workouts, and movement with activity targets that flex with your energy levels. On lower-energy dose days, gentler targets keep you moving without burning out.
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Log your Mounjaro or Wegovy injection in seconds. Track your pen, your dose level, and your injection site — so you always know exactly where you are in your treatment.
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Log your weight, measurements, and how you're feeling after each dose. GLPTrackr turns your data into clear, motivating charts that show you how far you've really come.
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Frequently asked questions.
The most widely prescribed once-weekly weight loss injections are Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are prescription-only medicines used alongside diet and lifestyle changes. Which medicine is suitable for you is a decision for your prescriber or doctor.
Yes, rotating injection sites is generally recommended to reduce the risk of skin reactions such as thickening under the skin. Common sites include the abdomen, outer thigh, and upper arm. Your patient information leaflet and prescriber can advise on the rotation approach that suits your medicine.
Nausea, constipation, diarrhoea, and indigestion are the most commonly reported side effects, especially when starting or after a dose change. Many people find these ease over time. If side effects are severe, persistent, or concerning, contact your healthcare professional promptly.
GLP Trackr logs each injection — date, time, dose strength, and site — and suggests your next rotation automatically. Dose reminders help ensure a weekly injection is not missed, and your full injection history is available to review or discuss with your prescriber.
Both medicines are prescription-only and prescribed only when a clinician has assessed that the benefits outweigh the risks for an individual. Suitability and safety are determined by your prescriber based on your full medical history — always follow their guidance and report any concerns promptly.