What Tirzepatide is
Tirzepatide is a dual agonist of the GLP-1 and GIP receptors, FDA approved as Mounjaro for type 2 diabetes and Zepbound for chronic weight management. It is the best-characterized compound on this page: dosing, kinetics, and the titration schedule all come straight from the prescribing information.
Commercial products ship as fixed-dose pens. The math below applies to multi-dose vials of lyophilized powder, where you control the concentration with the amount of bacteriostatic water you add.
What we do not know
- Outcomes beyond about three years are unpublished. The pivotal obesity trials ran 72 weeks.
- Whether the GIP component adds benefit independently of GLP-1 in humans, or mainly improves tolerability, is unsettled.
- How much of the weight lost is lean mass, and whether that matters clinically, is measured inconsistently across trials.
- None of the trial evidence was generated with compounded or research-grade material, which is what this page's reconstitution math is usually used for.
Reconstitution math
Concentration is everything: the same 10 mg vial gives a different draw for every amount of bacteriostatic water you add. The table uses the common 2 mL setup for each vial size, which puts every unit on a U-100 insulin syringe at 50 mcg for the default vial. Dashes mark draws too small to measure or larger than the syringe.
| Vial | BAC water | Concentration | 2.5 mg | 5 mg | 7.5 mg | 10 mg | 12.5 mg | 15 mg |
|---|---|---|---|---|---|---|---|---|
| 5 mg | 2 mL | 2.5 mg/mL | 100 u | - | - | - | - | - |
| 10 mg | 2 mL | 5 mg/mL | 50 u | 100 u | - | - | - | - |
| 15 mg | 2 mL | 7.5 mg/mL | 33.3 u | 66.7 u | 100 u | - | - | - |
| 30 mg | 2 mL | 15 mg/mL | 16.7 u | 33.3 u | 50 u | 66.7 u | 83.3 u | 100 u |
| 60 mg | 2 mL | 30 mg/mL | 8.3 u | 16.7 u | 25 u | 33.3 u | 41.7 u | 50 u |
Dosing and protocol
FDA Zepbound titration: 2.5 to 15 mg weekly, four weeks per step.
The labeled schedule starts at 2.5 mg weekly, a dose chosen for tolerability rather than effect, and steps up every four weeks. Each hold gives GI side effects (nausea, early satiety) time to settle before the next step. The labeled maximum is 15 mg weekly.
Pharmacokinetics
Tirzepatide has published human pharmacokinetics: peak around 24 hours after a subcutaneous dose. The curves below are normalized one-compartment models built from the cited half-life, the same math the Planner uses. They show shape and timing, not absolute blood levels.
How it is thought to work
Tirzepatide activates two incretin receptors at once, GLP-1 and GIP. Both slow gastric emptying and increase glucose-dependent insulin release; the GLP-1 arm also acts on hypothalamic appetite signaling. The dual action is why its trial results separate from single-agonist GLP-1 drugs, though the independent contribution of the GIP arm in humans is still argued.
What the evidence supports
This table grades how well each outcome has been studied in humans, not how well Tirzepatide works. A strong grade means the question was asked properly, and the answer may still have been negative. Nothing here is inherited from a drug class, a close analog, or the parent molecule of a fragment.
| Outcome | Strongest published evidence |
|---|---|
| Cardiovascular event reduction | Human RCT |
| Glycemic control in type 2 diabetes | Human RCT |
| Obstructive sleep apnea severity | Human RCT |
| Weight loss | Human RCT |
| Lean mass preservation | Human, observational |
Storage and handling
Lyophilized vials keep best cold, dark, and dry; refrigeration is the community default and freezing lyophilized powder is common for long holds. After reconstitution, refrigerate at 2 to 8 C, do not freeze the solution, and date the vial. Bacteriostatic water's preservative keeps multi-dose use practical for about 28 days by USP convention, though our 120-day stability study found the preservative itself outlasts that window.
The commercial pens are labeled for refrigeration, with a limited room-temperature window (21 days for Zepbound per its labeling). Treat reconstituted vials more conservatively: refrigerate at 2 to 8 C and date the vial the day you mix it.
Got a certificate of analysis with your vial? Run it through our COA Reader: it reads the report in plain English, checks purity and mass against the label claim, and links the testing lab’s own verification page. Our guide to reading a COA explains what the numbers do and do not tell you.
Sources
- Zepbound prescribing information (Eli Lilly, 2024)Prescribing information
- Furihata et al., Population pharmacokinetics of tirzepatide, Clin Pharmacol Drug Dev 2024PMID 38356317
- Jastreboff et al., Tirzepatide once weekly for obesity (SURMOUNT-1), NEJM 2022PMID 35658024 · DOI