A reminder app is a starting point — not a health tracker. Here's why the days between your shots are the most important ones to understand, and why one app actually shows you what's going on.
It's Friday. Your weekly semaglutide shot was Monday. The hunger is creeping back. The energy feels a little flatter. You open PepTracker — and it tells you your next dose is in three days.
That's it. That's all it has for you.
It doesn't tell you how much compound is still active. It doesn't explain why Friday feels different from Tuesday. It doesn't show you the curve of your levels over the week, or where you are on that curve right now. It just counts down to the next alarm — and leaves you alone with the anxiety in between.
That gap — between the alarm and the actual understanding — is exactly what separates a reminder app from a real health tracker. PepTracker fills the first role capably. It was never designed for the second.
PepTracker is a mobile dose-logging app designed to help users remember their injection schedule. You enter your compound, your dosing interval, and the date of your last shot. The app records it and reminds you when the next one is due.
For that specific job — "don't forget your injection day" — it works. It's clean, it's simple, and it's free. The problem isn't what it does. The problem is where it stops.
PepTracker has no concept of pharmacokinetics. It doesn't know that a tirzepatide dose has a half-life of roughly five days — meaning that by day six, your active level has fallen significantly below its peak. It doesn't show you whether your compound is still meaningfully working on Wednesday, or whether the fatigue you feel on Saturday is directly correlated with your trough. It doesn't have that data. It has a calendar.
The most important pharmacokinetic fact about GLP-1s and many peptides is that they don't disappear the moment you inject them — and they don't stay at full strength until the moment you inject again. They follow a smooth, predictable curve: peak shortly after injection, then gradually declining toward trough. Published pharmacology on GLP-1 receptor agonists confirms that this curve follows first-order elimination kinetics, making it entirely calculable in real time.
Here is what that week actually looks like in each app:
| Day | Halflife — Peptide & GLP-1 Log | PepTracker |
|---|---|---|
Monday Injection day |
✓ Dose logged. Level curve begins at 100% and rising. Dose saved to history with timestamp. | ✓ Dose logged. Next reminder set. App goes quiet. |
Wednesday Mid-week |
✓ Active level ~75%. Curve shows compound still near peak — you can see and feel why. Full clarity on where you stand. | ✗ Silence. No data. No curve. The app has nothing for you until Sunday. |
Friday Pre-trough |
✓ Active level ~45%. Curve is declining toward trough. You understand exactly why Friday feels different. No anxiety — just information. | ✗ Still nothing. The hunger is back and the app offers no explanation for why. |
Sunday Next dose |
✓ Active level ~20%. Curve confirms trough. Smart reminder fires at the right time — not just seven days later by default. | ✓ Alarm fires. Same as last week. Countdown resets. |
PepTracker shows up on Monday and Sunday. Halflife is with you every day in between.
Many GLP-1 users describe a pattern near the end of their weekly cycle: increased hunger returning, energy dipping, the original symptoms quietly reasserting themselves. It's sometimes called the "weekly crash" — and it's entirely normal. It's just pharmacokinetics working as expected.
But without a visual of your curve, it feels unpredictable. It feels like the medication stopped working. It can cause anxiety, second-guessing, and the kind of health spiral that makes a simple routine feel exhausting.
When you can see the curve, the crash stops being a mystery. It becomes a predictable, manageable point on a graph — something that happens because your medication is working exactly as intended. That visibility alone is worth the switch from a reminder app to a real tracker.
| Feature | Halflife — Peptide & GLP-1 Log | PepTracker |
|---|---|---|
| Alarm Reminders | ✓ Smart reminders timed to your actual pharmacokinetic curve — not just a fixed interval from your last injection | ✓ Reliable interval-based reminders — the core feature, and it works well |
| Visual Body Levels | ✓ Real-time color-coded decay curves per compound, updated continuously between every dose you log | ✗ No concept of active levels — the app has no pharmacokinetic model |
| Crash Prevention | ✓ Seeing your trough approach in advance removes the guesswork and anxiety of the weekly cycle | ✗ No visibility between doses means no early warning — the trough arrives as a surprise every week |
| Setup Ease | ✓ Add from the built-in database of 45+ compounds, log your first dose, dashboard is live in minutes | ✓ Simple setup — enter a compound name and an interval and you're running |
PepTracker is built around a single-compound, single-interval model. That works cleanly if your entire health protocol is one weekly injection and nothing else.
But many people using GLP-1s are also running recovery peptides like BPC-157, or growth hormone secretagogues on a twice-daily schedule, or TRT on a different weekly rotation. The moment you have more than one compound, PepTracker gives you more than one separate reminder with zero visibility into how any of them interact or overlap.
Halflife handles everything in a single view. Every compound in your protocol database is tracked with its own curve, its own color, its own reminder — all on one screen, so you can see not just when to inject but what's actually happening across your entire routine at any given moment.
Free to download. Your visual body-level dashboard is ready in minutes — see exactly what's active, what's fading, and when to act next.
↓ Download Halflife FreePepTracker is a capable, simple reminder app. If the only thing you need is a nudge on injection day, it does that well. But if you've ever felt the Friday fade and wanted to understand it, or if you've ever wondered whether your dose is still working mid-week, PepTracker has nothing to offer you.
Halflife — Peptide & GLP-1 Log was built for the full week — not just the two days when you interact with your calendar. It turns the silence between your shots into something visible, understandable, and reassuring. That's the difference between a reminder and a real health tracker.