GLP-1 Half Life Calculator

Why semaglutide and tirzepatide have weekly dosing

Semaglutide (Wegovy, Ozempic) has an exceptionally long half-life of ~7 days (168 hours), achieved through fatty acid modification that enables albumin binding — this slows renal filtration and enzymatic degradation. At a 7-day half-life, once-weekly dosing maintains relatively stable plasma concentrations. Tirzepatide (Zepbound, Mounjaro) has a half-life of ~5 days (120 hours), similarly supporting weekly dosing.

Liraglutide (Saxenda) has a much shorter half-life of ~13 hours, requiring daily injections. Despite similar mechanisms, the structural differences between GLP-1 receptor agonists produce markedly different PK profiles.

How long does Ozempic or Wegovy stay in your system?

Using the 5 half-life rule: semaglutide (7-day t½) reaches 95% elimination approximately 24 days after the last dose and 99% elimination in about 47 days. In practice, detectable semaglutide levels persist for 4–7 weeks post-injection.

Liraglutide (Saxenda) with its 13-hour t½ is essentially eliminated within 3–4 days. Tirzepatide (5-day t½) clears within approximately 17 days to 95% and 33 days to 99%.

Time to steady state

Steady-state plasma concentrations (within ~3% of true steady state) are reached after approximately 5 half-lives. For semaglutide (7-day t½), this is ~35 days (5 weekly injections). For tirzepatide (5-day t½), this is ~25 days. Weekly GLP-1 injections therefore achieve relatively stable plasma levels within 4–5 weeks.