Key takeaways
- These medicines usually start at a low dose and step up. The first doses are not the full dose.
- With weekly dosing, the amount in the body builds over several weeks before it levels out.
- The label, and your prescriber, give the schedule. This article gives no doses; the steps are on the labels.
- Reko records your doses and how you feel, so you can see change as it happens.
Why it is not instant
Most of these medicines are started low and raised in steps. This gives the body time to adjust. It also means the first weeks are not at the dose that may eventually be used. The step schedule is set by the label and your prescriber: on the U.S. labels, Ozempic goes up after 4 weeks on its starting dose, Wegovy injection goes up every 4 weeks over its first 16 weeks, and Mounjaro and Zepbound go up in 2.5 mg steps after at least 4 weeks on the current dose (Mounjaro, Zepbound, Ozempic, Wegovy).
Why it builds up
A drug that leaves the body slowly, taken once a week, accumulates before it settles into a steady pattern. The time this takes depends on its half-life: semaglutide has a half-life of approximately 1 week and reaches steady state after 4 to 5 weeks of weekly doses (Ozempic label), and tirzepatide has a half-life of approximately 5 days, or 5 to 6 days on the Zepbound label, with steady state after 4 weeks. Reko draws an estimated level from your doses and the compound's published half-lives, so you can see the shape. It is an estimate, not a blood test.
When effects show up
Effects on appetite, on weight and on blood sugar do not all arrive together. Label and trial data describe when they were measured in studies: in adults with obesity or overweight and no diabetes, the Wegovy label reports an average body-weight change of -14.9% on Wegovy against -2.4% on placebo at week 68, and the Zepbound label reports -15.0%, -19.5% and -20.9% on 5, 10 and 15 mg against -3.1% on placebo at week 72. In type 2 diabetes, the Mounjaro label reports HbA1c falling by 1.8, 1.7 and 1.7 points on 5, 10 and 15 mg against 0.1 on placebo at 40 weeks. Individual results differ widely. Do not compare your week three with someone else's.
What can change the timing
- The dose and where you are in the step schedule.
- Missed or late doses.
- Other medicines and health conditions.
- Food, sleep, activity and hydration.
Your prescriber is the right person to ask whether your progress is as expected.
What to record while you wait
- Every dose, with the date and site.
- Weight, on the same terms each time.
- Side effects, beside the dose they followed. How.
- Protein, water and food against your own targets.
When you see your care team, a few weeks of notes tell a better story than memory does.
Questions
Should I raise my dose if I see no change?
That is a decision for your prescriber. Reko never suggests a dose.
Is the level curve a measurement?
No. It is an estimate from your logged doses and published half-lives.
- Mounjaro prescribing information on DailyMed (Eli Lilly and Company, Novo Nordisk). Checked 2 November 2026.
- Zepbound prescribing information on DailyMed (Eli Lilly and Company, Novo Nordisk). Checked 2 November 2026.
- Ozempic prescribing information on DailyMed (Eli Lilly and Company, Novo Nordisk). Checked 2 November 2026.
- Wegovy prescribing information on DailyMed (Eli Lilly and Company, Novo Nordisk). Checked 2 November 2026.