Free Tool
GLP-1 Medication Level Calculator
This is the medication level (half-life) calculator: it estimates how much semaglutide or tirzepatide is in your body on each day of the dose week, so you can see when your Ozempic, Mounjaro, Wegovy, or Zepbound peaks and plan meals around side effects. For protein, injection sites and medication comparison, see all GLP-1 calculators.
How This Calculator Works
Pharmacokinetic Model
Uses a clinically-validated one-compartment pharmacokinetic model with first-order absorption and elimination. Based on published half-life and bioavailability data for each medication.
Personalized Calculations
Adjusts for your body weight to calculate volume of distribution. Heavier individuals have different concentration curves than lighter individuals, even at the same dose.
Evidence-Based
All medication parameters sourced from FDA prescribing information and peer-reviewed pharmacokinetic studies. We use published data, not estimates or guesses.
Understanding Your Medication Levels
What is Half-Life?
Half-life is the time it takes for your body to eliminate 50% of the medication. Semaglutide (Ozempic, Wegovy) has a half-life of approximately 7 days, while Tirzepatide (Mounjaro, Zepbound) has a half-life of about 5 days. This is why you inject weekly—medication levels remain elevated between doses, providing continuous appetite suppression and blood sugar control.
Why Peak and Trough Levels Matter
Understanding when your medication peaks and drops helps you optimize your GLP-1 experience:
- Peak Levels (highest concentration) typically occur 1-3 days after injection and correlate with the strongest side effects (nausea, fatigue). This is also when appetite suppression is most powerful.
- Trough Levels (lowest concentration) occur just before your next dose and may result in increased hunger or reduced fullness. Some people describe this as "food noise" returning.
How to Use This Information
Use your medication level graph to make informed decisions:
- • Meal Planning: Eat light, protein-rich meals when levels are high to minimize nausea
- • Activity Scheduling: Avoid intense exercise or social events during peak days if you experience fatigue
- • Timing Optimization: Consider injecting in the evening if you experience daytime side effects—this shifts the peak to nighttime when you're sleeping
- • Steady State: After 4-5 doses, your levels will reach steady state, and side effects often improve as your body adapts
Tips for Using This Information
Plan Meals Around Peak Times
When your levels are highest (1-3 days after injection), prioritize protein-rich, easy-to-digest meals. Avoid high-fat or fried foods during this window to minimize nausea. Save challenging social meals for when levels are moderate.
Track Side Effects
Keep a journal of side effects and compare them to your medication level graph. You may notice patterns—like nausea always occurring on Day 2-3. This knowledge helps you prepare and adjust your schedule accordingly.
Optimize Injection Timing
If you experience daytime nausea, try switching to evening injections. This shifts your peak to nighttime when side effects are less disruptive. Experiment to find what works best for your lifestyle.
Discuss with Your Doctor
Share your graph with your healthcare provider. If you experience a large trough-to-peak swing, they may recommend a shorter dosing interval (e.g., every 5 days instead of weekly) for more consistent coverage.
Frequently Asked Questions
What is the half-life of semaglutide and tirzepatide?
Semaglutide (Ozempic, Wegovy, Rybelsus) has a half-life of approximately 7 days; tirzepatide (Mounjaro, Zepbound) approximately 5 days. That is why both are dosed weekly and why levels build up over the first 4-5 weeks of a new dose.
Why does my appetite come back at the end of the week?
Medication levels decline through the dose week after peaking in the first 1-3 days. As levels fall, appetite suppression weakens, which many users notice on days 5-7. The chart shows exactly where you are in that curve.
How do I track my medication levels day to day?
The GLP AI app includes this medication level chart alongside dose tracking, the GLP-1 Meal Score, and a side-effect log, so levels, meals, and symptoms sit on one timeline. This calculator is educational and does not provide medical advice.
How accurate is this calculator?
This calculator uses a clinically-validated one-compartment pharmacokinetic model based on published data from FDA prescribing information and peer-reviewed studies. The calculations are accurate for population-level estimates. However, individual responses vary based on factors like genetics, metabolism, kidney and liver function, body composition, and other medications. This tool provides educational estimates—not diagnostic results. Always consult your healthcare provider for personalized medical advice.
What is a half-life and why does it matter?
Half-life is the time it takes for your body to eliminate 50% of the medication. Semaglutide has a half-life of ~7 days, while tirzepatide has a half-life of ~5 days. This long half-life is why you inject weekly—the medication stays in your system long enough to provide continuous effects between doses. Understanding half-life helps you predict when levels will be highest (strongest effects) and lowest (time for next dose).
When will I feel the strongest effects of my medication?
Most people feel the strongest effects 1-3 days after injection, when medication levels peak. This is when appetite suppression is most powerful, but it's also when side effects like nausea or fatigue are most likely. The graph shows your personalized peak time based on your dose and body weight. Effects become more predictable after reaching steady state (4-5 doses).
Why do I feel different effects at different times of the week?
Your medication levels fluctuate throughout the week. They're highest 1-3 days after injection (peak) and lowest just before your next dose (trough). This creates a predictable pattern: stronger appetite suppression and more side effects at peak, potentially more hunger and fewer side effects at trough. Tracking this pattern can help you optimize meal planning, exercise timing, and social activities.
Should I change my dosing schedule based on these results?
Never adjust your medication dose or schedule without consulting your healthcare provider. This calculator is for educational purposes only and does not provide medical advice. However, you can share your results with your doctor. If you experience severe side effects or notice your levels drop significantly before the next dose, your provider may consider adjusting your dosing interval (e.g., injecting every 5 days instead of weekly).
Can I use this calculator for compounded medications?
Yes! Compounded semaglutide and tirzepatide use the same active ingredients as brand-name medications (Ozempic, Wegovy, Mounjaro, Zepbound), so they have identical pharmacokinetics. Simply select the medication type (semaglutide or tirzepatide) and enter your custom dose. The calculations will be accurate regardless of whether your medication is branded or compounded.
What's the difference between semaglutide and tirzepatide levels?
Semaglutide (Ozempic, Wegovy) has a longer half-life (~7 days) compared to tirzepatide (Mounjaro, Zepbound, ~5 days). This means semaglutide levels fluctuate less between doses and stay elevated longer. Tirzepatide levels drop faster, which may result in more noticeable appetite fluctuations toward the end of your dosing cycle. Both medications are highly effective—the choice depends on your individual response and provider recommendation.
Is this calculator FDA-approved or a substitute for medical advice?
No. This calculator is for educational and informational purposes only. It is not FDA-approved, not a medical device, and not a substitute for professional medical advice, diagnosis, or treatment. The calculations are based on population averages and may not reflect your individual response. Individual metabolism, medical conditions, and other factors affect how your body processes medication. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding medication or health. If you think you may have a medical emergency, call your doctor or emergency services immediately.
Medical Disclaimer
This calculator is for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. The medication concentration calculations are based on published pharmacokinetic data and population averages. Individual responses to medication vary based on many factors including genetics, metabolism, kidney and liver function, body composition, other medications, and medical conditions. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have seen on this calculator. If you think you may have a medical emergency, call your doctor or emergency services immediately.