The Science Behind How Slimming Injections Work
Both Mounjaro and Wegovy are once-weekly injectable medicines that mimic naturally occurring gut hormones involved in appetite regulation.
GLP-1 receptor agonists
Wegovy contains semaglutide, which acts on GLP-1 (glucagon-like peptide-1) receptors. GLP-1 is a hormone released after eating; it signals to the brain that you are full, slows the rate at which the stomach empties, and reduces appetite. By activating these receptors more consistently, semaglutide helps many people feel satisfied with smaller amounts of food.
Dual GIP and GLP-1 action
Mounjaro contains tirzepatide, which acts on both GLP-1 receptors and GIP (glucose-dependent insulinotropic polypeptide) receptors. GIP is another gut hormone involved in energy balance and fullness signalling. This dual action is what makes tirzepatide distinct from single-pathway medicines, though how any individual responds is determined by their own physiology and is something to discuss with their prescriber.
What this means day to day
In practical terms, many people commonly report:
- Reduced appetite and less frequent hunger
- A quieter relationship with food — often described as reduced "food noise"
- Feeling full more quickly during meals
- Slower stomach emptying, which can contribute to nausea, particularly early on or after a dose adjustment
These effects are commonly reported but not universal, and they tend to be most noticeable in the early weeks of treatment. For a broader look at how these medicines are used, see our guide to weight-loss injections and the related piece on how weight-loss injections work.
According to NHS guidance, both medicines are prescription-only and are used alongside a reduced-calorie diet and increased physical activity as part of a managed weight-loss programme.
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.
AI Meal Tracking. Built for GLP 1 Appetites.
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How GLP Trackr Helps You Understand Your Injection Journey
Knowing the mechanism is one thing — seeing how your own body is responding is another. GLP Trackr's injection-site tracking and rotation feature lets you log every dose, the site used (abdomen, thigh, or upper arm), and the date and time. The app then keeps a rotation history and suggests your next site, so you never have to guess or repeat the same spot unnecessarily.
Alongside that, the side-effect tracker lets you log symptoms like nausea, fatigue, or indigestion and view them over time — useful context to bring to your next appointment. And the dose reminder feature means a once-weekly injection is much harder to accidentally forget, keeping your schedule consistent from week one.
If you want to explore what others on this journey have found helpful, the slimming injections overview and our page on whether weight-loss injections work are good places to continue reading.
GLP Trackr is a tracking and journaling companion — it supports you in understanding your own patterns and staying consistent, but it is not a substitute for your prescriber's guidance. Any questions about how the medicine is affecting you, or whether your dose is right, should always go to your prescriber or doctor.
Ready to start making sense of your injection journey? Download GLP Trackr on the App Store or Google Play — your first 7 days are completely free.
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.
Slimming injections like Wegovy (semaglutide) and Mounjaro (tirzepatide) act on gut hormone receptors — GLP-1 and, for tirzepatide, also GIP — that signal fullness to the brain and slow stomach emptying. Many people commonly report reduced hunger and less preoccupation with food as a result.
Many people notice some reduction in appetite within the first few weeks, though this varies between individuals. The full effect typically builds gradually as the dose is adjusted by a prescriber over time. Always follow your prescriber's guidance on what to expect at each stage.
No. Mounjaro and Wegovy are not insulin. They are GLP-1 receptor agonists (and in Mounjaro's case, also a GIP receptor agonist) that act on appetite and fullness pathways. They work differently from insulin and are prescribed for different purposes.
Nausea is a commonly reported effect linked to slower stomach emptying — a result of how these medicines act on the gut. It is often most noticeable after a dose adjustment and tends to ease over time. If nausea is severe or persistent, contact your healthcare professional.
Yes. GLP Trackr lets you log each injection, track side effects like nausea or fatigue over time, and rotate injection sites with the app's prompts. This gives you a clear record to discuss at prescriber appointments — though the app is a tracking tool, not a source of medical advice.