Tirzepatide (Mounjaro, Zepbound, LY3298176) has an elimination half-life of approximately 5 days (120 hours)[1], based on population pharmacokinetic modeling across 19 pooled clinical studies per FDA NDA 215866. A C20 fatty diacid moiety enables reversible albumin binding (>99% protein bound), extending plasma residence from minutes to 5 days[2]. This pharmacokinetic profile supports once-weekly subcutaneous dosing. Steady state is reached after approximately 4 weekly injections, with trough concentrations approximately 1.7-fold higher than after a single dose[1].
| Parameter | Value | Source |
|---|---|---|
| Elimination Half-Life | ~5 days (120 h; mean 5.4 days) | [1] |
| Time to Peak (Tmax) | 8–72 h (median ~24 h) SC | [1] |
| Route(s) of Administration | Subcutaneous injection | — |
| Plasma Protein Binding | >99% (albumin) | [1] |
| Time to Steady State | ~4 weeks (4 once-weekly doses) | [2] |
| Accumulation at Steady State | ~1.7× | [1] |
| Full Clearance (5 half-lives) | ~25 days | Calculated |
| Standard Dosing Frequency | Once weekly | [1] |
| Data Quality | Human RCT — half-life from population PK modeling of 19 pooled RCTs | — |
Tirzepatide has an elimination half-life of approximately 5 days (mean 5.4 days, 120 hours) based on population pharmacokinetic modeling across 19 pooled clinical studies[1]. This was established using nonlinear mixed-effects modeling of data from patients with type 2 diabetes and obesity across multiple Phase 3 trials. The population PK approach provides a robust estimate across diverse patient populations, weight ranges, and renal function categories.
The extended half-life relative to native GIP (~7 minutes) and GLP-1 (~2 minutes) is entirely a consequence of the C20 fatty diacid modification. Without this structural feature, tirzepatide would be rapidly degraded by dipeptidyl peptidase-4 (DPP-4) and cleared renally within minutes[2].
The half-life of tirzepatide is measured using population pharmacokinetic modeling rather than simple two-point blood sampling, because the drug accumulates over multiple doses before reaching steady state. Blood samples are collected at multiple time points across 19 clinical studies, and a nonlinear mixed-effects model fits the observed concentration-time data to estimate parameters including elimination rate constant (from which half-life is derived as ln(2)/kel)[2].
Tirzepatide's plasma half-life of approximately 5 days describes how quickly it clears from circulation. Its biological effects — appetite suppression, gastric emptying delay, glycemic control — are governed by GIP and GLP-1 receptor occupancy, which is concentration-dependent. At steady state, trough concentrations (days 5–7 post-injection) remain above the threshold for meaningful receptor activation, meaning biological effects persist continuously throughout the once-weekly interval despite fluctuating plasma concentrations[1].
After the last dose of tirzepatide, plasma concentrations decline according to the ~5-day half-life. The 5-half-life clinical clearance threshold (approximately 97% eliminated) is reached approximately 25 days after the final injection. This washout period is clinically relevant for patients planning pregnancy, as tirzepatide is not recommended during pregnancy, and for patients undergoing elective surgery who may need to pause treatment.
| Half-Lives Elapsed | Time After Last Dose | % Remaining in Plasma |
|---|---|---|
| 1 | ~5 days | 50% |
| 2 | ~10 days | 25% |
| 3 | ~15 days | 12.5% |
| 4 | ~20 days | 6.25% |
| 5 (clinical clearance threshold) | ~25 days | ~3% |
After a single subcutaneous injection, tirzepatide reaches peak plasma concentration (Tmax) in approximately 8–72 hours (median ~24 hours). Concentrations then decline mono-exponentially with a half-life of approximately 5 days. After a single dose, approximately 97% is cleared by day 25.
At steady state (reached after approximately 4 weekly doses), trough concentrations are approximately 1.7-fold higher than after a single dose[1]. This accumulation is predictable from the half-life: because the dosing interval (7 days) is longer than the half-life (5 days), moderate accumulation occurs until input equals output. The peak-to-trough ratio at steady state is relatively modest compared to shorter half-life compounds.
The ~5-day half-life makes once-weekly dosing pharmacokinetically sound: the dosing interval (7 days) is long enough that concentrations do not excessively accumulate (preventing toxicity), yet short enough that trough concentrations remain above the therapeutic threshold throughout the interval. With weekly dosing, steady-state trough concentrations maintain GIP and GLP-1 receptor engagement continuously[1].
If a weekly tirzepatide dose is missed, plasma concentrations decline by approximately 12–13% per day after the scheduled injection time. A dose missed by 2–3 days results in approximately 25–37% lower trough concentrations. The FDA prescribing information for Mounjaro states that a missed dose may be administered within 4 days; beyond 4 days, skip the missed dose and resume the regular schedule[1].
| Compound | Half-Life | Dosing Frequency | Approval Status |
|---|---|---|---|
| Tirzepatide (Mounjaro/Zepbound) | ~5 days | Once weekly | FDA-approved NDA 215866 |
| Semaglutide (Ozempic/Wegovy) | ~7 days | Once weekly | FDA-approved NDA 209637 |
| Liraglutide (Victoza/Saxenda) | ~13 hours | Once daily | FDA-approved |
| Retatrutide | ~6 days | Once weekly | Phase 3 trial |
| Route | Half-Life | Bioavailability | Tmax | Notes |
|---|---|---|---|---|
| Subcutaneous | ~5 days | ~80% (estimated) | 8–72 h (median ~24 h) | Standard FDA-approved route |
| Intravenous | ~5 days | 100% | Minutes | Reference PK route; not approved for clinical use |
| Intramuscular | No published data | No published data | No published data | Not an approved route |
| Oral | No published data | No published data | No published data | Oral formulation not currently approved |
Tirzepatide is an FDA-approved prescription medication (NDA 215866 / NDA 217806) and is not included in standard WADA anti-doping panels or workplace substance abuse drug test panels. Standard immunoassay urine drug screens will not detect tirzepatide.
Specialized liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays can detect tirzepatide in plasma and urine. No formal forensic detection window study has been published for tirzepatide. If subject to drug testing in any context, disclose all prescription medications including tirzepatide to the testing agency. FDA-approved medications are typically disclosed separately from controlled substance screening panels.
The ~5-day half-life of tirzepatide is almost entirely attributable to its C20 fatty diacid moiety — a 20-carbon fatty acid chain attached to the lysine at position 20 of the tirzepatide backbone via a linker[2]. This fatty acid chain binds reversibly and non-covalently to albumin (the most abundant plasma protein), which accounts for more than 99% of plasma protein binding. Albumin acts as a pharmacokinetic reservoir: bound tirzepatide is protected from renal filtration (albumin's large molecular weight prevents glomerular filtration) and from proteolytic enzymes that would otherwise cleave the peptide rapidly.
Additionally, tirzepatide contains an aminoisobutyric acid (Aib) substitution at position 2 of the peptide backbone. This modification prevents cleavage by dipeptidyl peptidase-4 (DPP-4), an enzyme that would otherwise rapidly inactivate GLP-1-like peptides at the alanine-2 position within minutes. Without Aib, tirzepatide would share the same ~2-minute half-life as endogenous GLP-1[2].
Clearance of tirzepatide occurs via proteolytic degradation (endopeptidases cleave the backbone once the fatty acid dissociates from albumin), followed by renal and biliary excretion of the resulting smaller peptide fragments. The rate-limiting step is dissociation from albumin, which is governed by the binding affinity of the C20 fatty diacid — and this affinity determines the ~5-day effective half-life.
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