The Brand Names and Active Substances Behind Weight Loss Injections
Prescription weight loss injections are known by both a brand name and an active substance name. The brand name is the commercial label given by the manufacturer; the active substance is the medicine itself.
Mounjaro (tirzepatide)
Mounjaro is the brand name; tirzepatide is the active substance. Tirzepatide acts on two receptors — GIP and GLP-1 — that are involved in regulating appetite and blood sugar. It is supplied as a pre-filled pen and is taken once a week by injection under the skin. Common injection sites include the abdomen, thigh, and upper arm.
Wegovy (semaglutide)
Wegovy is the brand name; semaglutide is the active substance. Semaglutide acts on GLP-1 receptors, which play a role in feelings of fullness and appetite regulation. Like Mounjaro, it comes as a pre-filled pen for once-weekly subcutaneous injection, using the same general site options.
Why the name matters
Both medicines are prescription-only. Suitability and dosing are decided entirely by your prescriber or doctor based on your individual health history — not by the brand name alone. If you have seen either name referenced in a different context (for example, semaglutide is also sold under a different brand name for type 2 diabetes management), your prescriber will have prescribed the specific product appropriate for you.
Both Mounjaro and Wegovy carry a black triangle (▼) designation in some countries, meaning they are subject to additional monitoring. Any side effects should be reported to your healthcare professional and, where applicable, to your national reporting scheme (such as the UK's Yellow Card scheme).
For a broader overview of how these medicines fit into the wider landscape, see our guide to weight loss injections.
average weekly weight change in the first 16 weeks of Mounjaro & Wegovy use*
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How GLP Trackr Helps You Stay on Top of Your Injection Routine
Remembering which site you used last week — and which pen you are currently on — is one of the small but real challenges of a once-weekly injection schedule. GLP Trackr's injection-site tracking is built for exactly this: log each injection with the site (abdomen, thigh, or upper arm) and the app keeps a rotation history so it can suggest where to inject next, helping you avoid overusing any single area.
Alongside site rotation, the app logs your dose and date for each injection, so you always have a clear record of where you are in your schedule. And if your weekly shot day is easy to overlook amid a busy routine, dose reminders give you a gentle nudge so a pen is never forgotten.
Having this record also means you arrive at prescriber appointments with a clear, factual log of your injections — useful context for any conversation about how your treatment is going.
Always follow the guidance of your prescriber or doctor regarding injection technique and any changes to your routine — they know your full medical history and the specific product you have been given.
Curious about what different prescriptions cost or how pricing works? You can read more about weight loss injection pricing or explore finding well-priced weight loss injections for general context.
Log your injection sites, track your rotation, and keep your weekly schedule on track — download GLP Trackr free on the App Store or Google Play and start a 7-day trial at no cost.
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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
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
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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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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.
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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.
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Frequently asked questions.
The two main prescription weight loss injections are Mounjaro, whose active substance is tirzepatide, and Wegovy, whose active substance is semaglutide. Both are once-weekly injectable medicines available only on prescription, with suitability and dosing decided by your prescriber or doctor.
The brand name (Mounjaro or Wegovy) is the commercial label; the active substance (tirzepatide or semaglutide) is the actual medicine. Your prescription will specify which product and dose strength your prescriber has chosen for you based on your individual health needs.
Rotating injection sites — across areas such as the abdomen, thigh, and upper arm — is generally recommended to help avoid skin reactions at any one spot. Your prescriber or the patient information leaflet that came with your pen will give you guidance specific to your medicine.
GLP Trackr lets you log each injection with the site used, dose strength, and date. The app tracks your rotation history and suggests your next site, and dose reminders help you stay on your once-weekly schedule. It does not provide medical or dosing advice.
No. Mounjaro contains tirzepatide, which acts on both GIP and GLP-1 receptors. Wegovy contains semaglutide, which acts on GLP-1 receptors. Both are prescription-only weight loss injections, but they are different medicines. Which is appropriate for you is a decision for your prescriber or doctor.