What Are These Weight Loss Injections and How Do They Work?
Tirzepatide (Mounjaro) and semaglutide (Wegovy) are both prescription-only, once-weekly injectable medicines used for weight management in adults. They work on appetite-regulating pathways in the body — semaglutide acts on GLP-1 receptors, while tirzepatide acts on both GLP-1 and GIP receptors. Many people report a noticeable reduction in appetite and food noise, along with an increased sense of fullness after eating.
How they are taken
Both medicines come as pre-filled injection pens and are typically injected once a week. Common injection sites include the abdomen, front of the thigh, and upper arm. Rotating between sites is widely recommended to avoid skin irritation or changes at any one spot — your prescriber or the patient information leaflet that came with your pen will guide you on technique.
Starting dose and adjustment
Both medicines are generally started at a lower dose, with adjustments made over time by the prescriber based on how you are getting on. The dose schedule is individual — it is not something to change without guidance from your prescriber or doctor.
Both medicines carry a black triangle (▼) status in the UK, meaning 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 factual overview of semaglutide, the electronic Medicines Compendium (eMC) holds the full prescribing information.
Common side effects to be aware of
Gastrointestinal effects — nausea, constipation, diarrhoea, indigestion — are among the most commonly reported, particularly in the early weeks or after a dose adjustment. Fatigue, headache, and injection-site reactions are also frequently noted. These effects vary from person to person. If anything feels severe, persistent, or worrying, contact your healthcare professional promptly.
For more detail on what to expect week to week, see our guide on starting a weight loss injection, and if supply has been a concern for you, our page on weight loss injection shortages covers what is known. You can also read about moving to your next injection stage for context on how the journey typically progresses.
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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Tracking Your Injection Journey with GLP Trackr
Staying consistent with a weekly injection is one of the most important parts of getting the most from your treatment — and that is where GLP Trackr is built to help.
Injection-site tracking and rotation
The app lets you log each injection, including the site you used (abdomen, thigh, or upper arm) and the date and dose. GLP Trackr then tracks your rotation history and suggests your next site automatically, so you never have to remember where you injected last week. Over time, you build a clear record of every dose in one place.
Reminders so you never miss a dose
A missed injection is easy to overlook on a weekly schedule. GLP Trackr sends gentle reminders so your injection day stays front of mind — and if you do miss a dose, the app helps you log it so you can have an informed conversation with your prescriber about next steps. Any decision about a missed dose belongs with your prescriber, not an app.
Bringing your data to appointments
The doctor report feature pulls together your logged doses, side effects, and progress into a clear summary — useful to bring to prescriber appointments so your clinician has the full picture.
GLP Trackr supports both Mounjaro and Wegovy users wherever they are in their journey. For a broader look at everything covered on injectable weight management, visit our weight loss injections hub.
GLP Trackr is a tracking and journaling app. It does not provide medical or dosing advice and is not a substitute for guidance from your prescriber or doctor. Always follow their instructions for your injection.
Ready to bring more clarity to your injection routine? Log your sites, track your rotation, and keep your weekly schedule on track — GLP Trackr is free to try for 7 days on the App Store and Google Play.
What does glptrackr include?
10+ powerful features. One app. Built specifically for Mounjaro and Wegovy users.
Everything your GLP-1 journey needs. Free to try for 7 days.
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
Personalized meal plans built around your current dose phase and side effects. Every meal is GLP-1 optimized — high in protein, gentle on the stomach, and scaled to your reduced appetite.
Recipe Library
Browse 50+ high-protein, GLP-1-friendly recipes filtered by meal type, prep time, and dietary needs. Every recipe includes full nutrition info, step-by-step instructions, and tips for eating with side effects.
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.
Exercise & Steps
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.
Community Support
Connect with thousands of others navigating the same medication journey. Share milestones, ask questions, find accountability partners, and get support from people who truly understand.
Never Forget a Dose Again.
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.
Watch Your Body Transform, Week by Week.
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.
You're Not on This Journey Alone.
Connect with thousands of real GLP-1 users sharing their wins, side effect tips, and meal ideas. Get the support of people who truly get it — because they're living it too.
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The Most Advanced GLP-1 Brain Ever Built.
The first AI built exclusively for GLP-1 weight loss. Every insight, every meal plan, every prediction trained on one thing only: helping you get the most out of your medication.
Knows Your Cycle
GLPIQ tracks where you are in your injection cycle and adjusts everything around it: lighter meals on nausea days, higher protein when appetite returns, and smarter targets as your medication level shifts.
Predicts Before You Feel It
GLPIQ learns your personal side effect patterns over time. After a few cycles, it starts warning you the morning before a rough day — and adjusts your meal plan automatically.
Finds Your Golden Dose
GLPIQ analyses every dose you've been on: weight loss rate, side effects, food noise, mood, protein adherence and tells you which dose gave you the best results. No other app does this.
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Frequently asked questions.
Tirzepatide (Mounjaro) and semaglutide (Wegovy) are both prescription-only injectable medicines for weight management. Which — if either — is appropriate for you is a decision for your prescriber or doctor based on your individual health history.
Common injection sites are the abdomen, front of the thigh, and upper arm. Rotating between sites is generally recommended to avoid skin irritation. Your prescriber or the patient information leaflet with your pen will guide you on technique.
Yes, rotating sites is widely recommended to help prevent skin changes or irritation at any single spot. GLP Trackr can log each site you use and suggest the next one automatically, making rotation easy to keep on top of.
Nausea, constipation, diarrhoea, and indigestion are among the most commonly reported effects, especially early on. Fatigue and injection-site reactions are also noted. If side effects are severe, persistent, or worrying, contact your healthcare professional promptly.
GLP Trackr logs each injection — site, dose, and date — tracks your rotation history, suggests your next site, and sends weekly reminders. It also generates a dose summary you can share with your prescriber at appointments.