Why levels build up at all
A weekly medicine with a long half-life is not gone when the next dose is due. Semaglutide’s half-life is about one week, so roughly half of each injection is still there seven days later, and the new dose lands on top of it [1].
Each week the leftover grows a little, and so does the amount the body clears, because more medicine is present to be cleared. After several weeks the two balance: what goes in each week matches what comes out. That balance is what the labels call steady state.
A simplified example
- Imagine a medicine whose half-life equals its weekly dosing interval, and call one dose “1”.
- Just after dose 1: 1. Just after dose 2: about 1.5. Dose 3: about 1.75. Dose 4: about 1.9. Dose 5: about 1.94.
- The level approaches a ceiling and the steps get smaller each week, which is why labels talk about weeks rather than a single day.
- This is arithmetic for illustration only. Real levels depend on absorption and on the person, and the labels report measured values instead. Trulicity®, for example, gives a measured accumulation ratio of about 1.56 at steady state [8].
What each label says
The figures below come from section 12.3 of each US label. Where a label leaves a cell empty, we say so rather than fill it in.
| Medicine | Half-life | Peak after a dose | Steady state reached | Still in the body after the last dose |
|---|---|---|---|---|
| Ozempic® injection, weekly [1] | About 1 week | 1 to 3 days | 4 to 5 weeks | About 5 weeks |
| Rybelsus® and Ozempic® tablets, daily [2] | About 1 week | About 1 hour | 4 to 5 weeks | About 5 weeks |
| Wegovy® injection or tablets [3] | About 1 week | 1 to 3 days (injection); 1 hour (tablet) | Not stated in the US label | About 5 to 7 weeks |
| Mounjaro®, weekly [4] | About 5 days | 8 to 72 hours | 4 weeks | Not stated |
| Zepbound®, weekly [5] | About 5 to 6 days | Median 24 hours (8 to 72) | 4 weeks | Not stated |
| Trulicity®, weekly [8] | About 5 days | 24 to 72 hours, median 48 | 2 to 4 weeks | Not stated |
| Foundayo™, daily [6] | About 29 to 49 hours | 4 to 8 hours | About 1 week | Not stated |
| Saxenda® and Victoza®, daily [7][9] | About 13 hours | 11 hours; 8 to 12 hours | Not stated | Not stated |
Where the documents disagree
For Wegovy®, the European product information fills a gap the US label leaves open. It says the tablets reach steady state after 4 to 5 weeks of daily use, and that injected semaglutide exposure stayed stable over time when checked up to week 72 [10]. The Canadian monograph for the injection puts the time semaglutide can remain in the circulation at about 7 weeks after the last 2.4 mg dose, at the top of the US range of 5 to 7 weeks [3][12].
None of these documents gives a time to steady state for liraglutide, though its 13-hour half-life and daily dosing mean it does not build up over weeks the way the weekly medicines do [7][9].
“Steady” is not flat
Even at steady state the level moves within each week. Per the Ozempic® label, semaglutide peaks 1 to 3 days after each injection; for tirzepatide the Mounjaro® label gives 8 to 72 hours [1][4]. The level then drifts down until the next dose.
What becomes steady is the pattern: from week to week, the peaks and troughs repeat at about the same height. That is also why the average steady-state values in labels are averages over a dosing interval, not a single reading.
Dose changes start a new climb
The labels describe exposure as dose-proportional. In the trial comparing two Ozempic® doses, the mean steady-state concentration was about 111 ng/mL with 1 mg and about 222 ng/mL with 2 mg, roughly double for double the dose [1]. The same arithmetic means that after a dose change the level moves toward a new balance over the following weeks rather than overnight.
Labels raise doses in steps of at least 4 weeks, but the reason they give is different: the Ozempic® label says the step-by-step increase is there to reduce the risk of stomach and gut side effects [1]. The schedule your prescriber sets is the one that applies to you.
Tablets settle with a wider spread
Semaglutide tablets reach steady state too, but where the level settles differs more from one person to the next. The Wegovy® label gives the range for 90% of patients: average levels of 27 to 186 nmol/L on the 25 mg tablet, against 51 to 110 nmol/L on the 2.4 mg injection [3]. In people with type 2 diabetes the tablet average was lower, about 44 nmol/L against 68 nmol/L with the injection.
Steady state helps here. A population model of the tablet trials estimated that absorption varied by 137% from day to day within the same person, but that daily dosing combined with the long half-life brought the variation in steady-state exposure down to about 33% [11].
Why labels measure at steady state
Many label numbers are taken once things have settled. The Ozempic® label, for example, reports its blood sugar measurements after 12 weeks of treatment, including the dose increases, at steady state with 1 mg. Drug interaction studies in the Saxenda® label were also run with liraglutide at steady state [1][7].
That is worth remembering when you compare your own early weeks with a label: the label usually describes the settled situation, not the first days. How you feel can also change on its own schedule; the Mounjaro® and Foundayo™ labels note that the delay in stomach emptying is greatest after the first dose and lessens over time [4][6].
Steady state also works in reverse
The same half-life that slows the build-up also slows the wash-out. After the last dose, semaglutide stays in the circulation for about five weeks according to the Ozempic® and Rybelsus® labels, which is why both ask for a long period of observation after an overdose and why the semaglutide labels ask women to stop at least 2 months before a planned pregnancy [1][2].
For a medicine with a short half-life the picture is quicker in both directions: Foundayo™ settles in about a week, and its label describes a period of observation after an overdose that takes its half-life into account [6].
Keeping a record of the early weeks
Because the first month is a period of change, a dated note next to each dose is more useful than memory: appetite, stomach symptoms, sleep and energy, written on the day. When doses go up, the same notes show how each step felt.
Ozempic®, Rybelsus®, Wegovy®, Saxenda® and Victoza® are registered trademarks of Novo Nordisk A/S. Mounjaro®, Zepbound® and Trulicity® are registered trademarks of Eli Lilly and Company, and Foundayo™ is a trademark of Eli Lilly and Company. PepLabo is not affiliated with or endorsed by Novo Nordisk or Eli Lilly and Company.
