How the drug builds up, week by week

How this plotter works

What is drawn is a relative concentration curve run out over 24 weeks of titration. Behind it sits a one-compartment model with first-order absorption and elimination — the Bateman equation — and the doses are superposed on one another so that accumulation toward steady state appears. The plateau at the maintenance dose is set to 100%, which makes the axis relative buildup rather than a blood level anyone could measure.

Where the approved drugs are concerned the ladders come off their FDA labels [1, 2, 3, 4, 5]. For retatrutide, still investigational, the ladder comes from its phase 2 trial registry entry:

• Semaglutide (Wegovy injection): 0.25 mg → 0.5 mg → 1 mg → 1.7 mg → 2.4 mg, increased every 4 weeks. For adult weight reduction the label allows up to 7.2 mg once weekly after at least 4 weeks at 2.4 mg. Ozempic uses its own ladder (0.25 mg → 0.5 mg, then 1 mg or 2 mg; 2 mg maximum)
• Tirzepatide (Zepbound / Mounjaro): 2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg, increased every 4 weeks
• Orforglipron (Foundayo): 0.8 mg → 2.5 mg → 5.5 mg → 9 mg → 14.5 mg → 17.2 mg, each step after at least 30 days; the steps above 5.5 mg depend on response and tolerability
• Retatrutide (LY3437943, investigational): 2 mg → 4 mg → 8 mg → 12 mg, the escalation used in the 12 mg arm of the phase 2 trial (NEJM 2023). The trial registry does not state how long each step lasted, so the chart assumes 4 weeks. Retatrutide is not yet FDA-approved; we include it for educational comparison only.

Half-life and steady state

One number explains more about how a GLP-1 feels over the weeks than any other, and it is the elimination half-life. Orforglipron taken by mouth sits at roughly 29 to 49 hours [5]; tirzepatide at about 5 days [8]; retatrutide, still investigational, near 6 [10]; and semaglutide longest of all, about 7 days [7]. After 4-5 half-lives of constant dosing the drug reaches steady state, which is the plateau the chart shows at the dashed reference line. The labels put that at 4 to 5 weeks for weekly semaglutide, about 4 weeks for weekly tirzepatide, and about 1 week for daily orforglipron [2, 4, 5].

The missed-dose simulator

Skip a weekly dose of semaglutide and, by the model, the level has roughly halved by the time the next dose is due; tirzepatide, with its shorter half-life, falls further. For Wegovy, take a missed dose as soon as possible if the next one is more than 2 days away, and otherwise skip it [1]. For Zepbound and Mounjaro the window is 4 days (96 hours) after the missed dose [3, 4].

The control beneath the chart will drop any single dose across those 24 weeks so you can watch the curve answer.

Important disclaimer

Educational only, and not medical advice. These curves are relative shapes drawn from published parameters; nobody should read them as the concentration in their own blood. What a real person carries varies a great deal with body weight, where the injection went, how the liver and kidneys are working, whatever else is being taken, and much besides. Decisions about dose belong with a qualified clinician. GLP Watchdog does not diagnose, does not treat, and does not tell you what to take.

Related research

The trial evidence behind each of them:

• Foundayo (orforglipron) FDA approval and ATTAIN-1 deep-dive
• Tirzepatide vs semaglutide head-to-head comparison
• What the trials recorded about side effects
• What happens when you stop semaglutide
• GLP-1 compounded pricing index