Three PK terms that are not interchangeable
Time to maximum concentration
When the population curve peaks
For injected semaglutide, the Ozempic and Wegovy labels say maximum concentration is reached one to three days after a dose. [1] [2] For injected tirzepatide, Mounjaro gives an 8-to-72-hour range; Zepbound gives a 24-hour median with the same range. [3] [4]
Elimination half-life
A decay parameter, not a “gone” date
The labels give semaglutide an approximate one-week half-life. Mounjaro gives tirzepatide an approximate five-day half-life; Zepbound gives about five to six days in its described populations. [1] [2] [3] [4]
Steady state
Repeated-dose context
The Ozempic label says steady-state exposure is reached after four to five weeks of once-weekly use. The Mounjaro and Zepbound labels say steady-state plasma concentrations are reached after four weeks of once-weekly use. These are label population estimates, not a personal concentration measurement. [1] [3] [4]
What the current U.S. labels say
These are descriptive label facts for the named products—not equivalent-dose comparisons and not directions for changing a schedule.
| Product / formulation | Maximum concentration | Steady state | Elimination language |
|---|---|---|---|
| Ozempic injection semaglutide | 1–3 days after a dose | 4–5 weeks of once-weekly use | About a 1-week half-life; present in circulation for about 5 weeks after the last dose. [1] |
| Wegovy injection semaglutide | 1–3 days after a dose | The current label reports average steady-state concentrations for the listed weekly injections; this table does not turn those averages into a personal level. | About a 1-week half-life; present in circulation for about 5–7 weeks after the last listed injectable dose. [2] |
| Mounjaro injection tirzepatide | 8–72 hours after a dose | 4 weeks of once-weekly use | About a 5-day half-life. [3] |
| Zepbound injection tirzepatide | 24-hour median; 8–72-hour range | 4 weeks of once-weekly use | About a 5–6-day half-life in the populations described by the label. [4] |
Scope note: the current Wegovy label also covers a daily oral tablet. This page and table are limited to the once-weekly injectable products, because oral and injected pharmacokinetics are not interchangeable. [2]
Model literacy
How to read a logged-dose model
This is a conceptual model-literacy frame, not a specification of any app’s algorithm.
1 · Logged input
An administration record
A logged-dose model starts with an administration record. A missing or incorrect entry means the model has a missing or incorrect input.
2 · Population parameter
A pharmacokinetic rule
The model applies an assumed pharmacokinetic parameter such as half-life. That parameter is an input, not a personal assay.
3 · Estimated output
A curve up to now
The output is an estimated curve from the doses logged, up to now. It is an estimate, not a measurement, and it does not predict symptoms or tell you when or how much to dose.
What the curve cannot prove
It is not a measurement
- It does not report an assayed blood concentration.
- It does not establish a personal therapeutic threshold.
- It does not show that a medicine is effective or ineffective.
It is not a symptom clock
- It cannot prove why hunger, nausea, fatigue, or another event happened.
- It cannot turn time to maximum concentration into a “strongest effects” day.
- It cannot choose a dose, titration, injection time, or schedule.
Injection site does not supply a shortcut
All four labels say overall exposure was similar after subcutaneous administration in the abdomen, thigh, or upper arm. That does not support using this page to claim that one of those sites produces a reliably faster personal peak. Follow the product’s administration instructions and take site questions to the prescriber. [1] [2] [3] [4]
Why “day 3” is not a symptom rule
A semaglutide label range of one to three days describes when maximum concentration is reached in pharmacokinetic data. It does not say appetite suppression, nausea, or any other effect must be strongest on day three. The tirzepatide labels likewise provide concentration timing—not a symptom schedule. Timing can be recorded as context, but proximity to a modeled peak does not establish cause. [1] [2] [3] [4]
Build a timing record a prescriber can read
Keep the observation separate from the interpretation. A concise record can preserve:
Exact product and formulation
Record the brand and whether the product is injected or oral. Do not substitute a class name for the exact label.
What actually happened
Keep the administration date and time, the prescribed amount as recorded, and any missed or changed event.
Neutral symptom timing
Write what was noticed and when. “Nausea began Tuesday morning” preserves sequence without declaring the cause.
The unresolved question
Keep “Is this timing meaningful?” as a question for the prescriber, not a conclusion produced by the graph.
For a fuller handoff structure, use the medication and protocol history guide. For symptom-specific label boundaries, use the GLP-1 side-effects guide.
Frequently asked questions
How long does semaglutide stay in the body?
The Ozempic label gives semaglutide an elimination half-life of about one week and says it remains in circulation for about five weeks after the last dose. The current Wegovy label also gives a roughly one-week half-life and says it remains in circulation for about five to seven weeks after the last listed injectable dose. Half-life is not the same as a personal stop date or a dosing instruction. [1] [2]
How long does tirzepatide stay in the body?
The Mounjaro label gives tirzepatide an approximate five-day elimination half-life. The Zepbound label gives about five to six days in the populations it describes. A half-life does not mean the medicine is fully gone after that interval. [3] [4]
Does a modelled level chart measure my blood?
No. A pharmacokinetic chart generated from logged administrations and population parameters is a model, not a blood draw or a measured personal concentration.
Does the highest modeled level predict the strongest appetite effect or side effects?
No. The labels report time-to-maximum-concentration ranges, but they do not establish a personal day-of-week rule for appetite, nausea, or other symptoms. Timing near a modeled peak does not prove causation. [1] [2] [3] [4]
Can a modeled curve tell me when to change a dose or schedule?
No. A modeled curve can organize timing context, but it cannot choose a dose, change a schedule, or determine whether a medicine is working. Those decisions belong with the current label and the prescriber.
Sources opened and checked
All four sources below were opened during this update. Label claims were checked against the full prescribing information, especially sections 12.2 and 12.3.
- [1]Ozempic (semaglutide) U.S. prescribing information, DailyMed: sections 12.2–12.3.
- [2]Wegovy (semaglutide) U.S. prescribing information, DailyMed: sections 12.2–12.3; injectable-product facts used here.
- [3]Mounjaro (tirzepatide) U.S. prescribing information, DailyMed: sections 12.2–12.3.
- [4]Zepbound (tirzepatide) U.S. prescribing information, DailyMed: sections 12.2–12.3.