How does tirzepatide work?

Tirzepatide is a single peptide molecule that acts as a dual agonist at two different receptors: the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor. Activating both receptors produces glucose-dependent insulin secretion, decreased glucagon secretion, slowed gastric emptying, and central appetite modulation — and in clinical trials yields greater glycemic and weight-loss effects than GLP-1 agonism alone.

What are the FDA-approved doses of tirzepatide?

Mounjaro (type 2 diabetes) and Zepbound (chronic weight management) are available in once-weekly pen doses of 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg. Treatment typically starts at 2.5 mg weekly for 4 weeks and titrates upward per the FDA label.

How do I reconstitute a compounded tirzepatide vial?

For a compounded 10 mg vial reconstituted with 1 mL bacteriostatic water (10 mg/mL), 1 unit on a 100-unit insulin syringe equals 100 mcg = 0.1 mg. A 2.5 mg dose equals 25 units; 5 mg equals 50 units; 10 mg equals 100 units (full syringe). For a 30 mg vial reconstituted with 1.5 mL (20 mg/mL), 1 unit equals 200 mcg, so 2.5 mg = 12.5 units, 5 mg = 25 units, 15 mg = 75 units. Commercial Mounjaro and Zepbound pens are pre-filled and are not reconstituted by the user.

How many units of tirzepatide equal 5 mg?

At 10 mg/mL (10 mg in 1 mL), 5 mg equals 50 units on a 100-unit insulin syringe. At 20 mg/mL (30 mg in 1.5 mL), 5 mg equals 25 units. At 5 mg/mL (10 mg in 2 mL), 5 mg equals 100 units (full syringe). The answer depends entirely on the concentration after reconstitution.

What happens if I miss a tirzepatide dose?

The FDA label for Mounjaro and Zepbound recommends administering a missed dose as soon as possible within 4 days (96 hours) of the missed scheduled dose. If more than 4 days have passed, skip the missed dose and resume the regular weekly schedule — this avoids excessive drug accumulation.

Dual GIP / GLP-1 receptor agonist · FDA-approved

Tirzepatide

Q: What is the half-life of tirzepatide?

Tirzepatide has an elimination half-life of approximately 5 days, which supports once-weekly subcutaneous dosing. Steady-state plasma concentrations are typically reached after about 4 weeks of consistent once-weekly administration.

Used for: chronic weight management (Zepbound) · type 2 diabetes (Mounjaro)

Tirzepatide is a synthetic once-weekly injectable peptide that activates both the GIP and GLP-1 receptors. It is approved by the FDA as Mounjaro (2022, type 2 diabetes) and Zepbound (2023, chronic weight management). Its approximately 5-day elimination half-life supports once-weekly subcutaneous dosing.

Class: Dual GIP + GLP-1 receptor agonist
Elimination half-life: ~5 days (~116.7 h)^[1][2][3]
Steady state reached: ~4 weeks of weekly dosing^[2]
Missed-dose window: Up to 4 days (96 h)^[1]
Approved doses: 2.5 · 5 · 7.5 · 10 · 12.5 · 15 mg weekly^[1]
Dosing route: Once-weekly subcutaneous
Brand names: Mounjaro · Zepbound
FDA status: Approved (multiple indications)

Educational reference only. Tirzepatide is a prescription medication. The FDA prescribing information for your product (Mounjaro or Zepbound) is the authoritative source for dosing, contraindications, and safety. Do not initiate, modify, or discontinue treatment without a qualified healthcare professional.

Last reviewed April 22, 2026 by the Enhanced Health Editorial Team. Reviewed for source alignment, FDA-status language, and medical-claim boundaries. See the editorial policy.

What tirzepatide is

Tirzepatide is a 39-amino-acid synthetic peptide engineered to activate two distinct incretin receptors in a single molecule: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). A C20 fatty-diacid side chain binds reversibly to serum albumin, producing an elimination half-life suitable for once-weekly dosing.^[2] It is manufactured by Eli Lilly and sold as two brand-name products with different indications and pen labeling: Mounjaro for type 2 diabetes and Zepbound for chronic weight management.^[1][3]

Mechanism

Tirzepatide binds and activates both the GIP receptor and the GLP-1 receptor. Downstream effects that contribute to its glucose-lowering and weight-loss activity include:^[3]

Glucose-dependent insulin secretion from pancreatic β-cells, via both GIP and GLP-1 signaling.
Suppression of glucagon secretion via GLP-1 receptor activation.
Delayed gastric emptying, reducing post-prandial glucose excursions and increasing satiety.
Central appetite modulation through GLP-1 and GIP receptors in appetite-regulating brain regions.
GIP-mediated adipose effects, which may contribute to the greater weight-loss efficacy observed versus GLP-1-only agonism in head-to-head trials.

Pharmacokinetics

Key parameters summarized from the FDA prescribing information and published population PK analyses:^[1][2]

Elimination half-life: approximately 5 days (roughly 116.7 hours).
Steady state: reached after about 4 weeks of once-weekly dosing.
PK model: best described by a two-compartment model with first-order absorption and elimination.
Dose range: population PK supports the approved once-weekly doses of 5, 10, and 15 mg; 2.5, 7.5, and 12.5 mg titration doses are also available.
Special populations: no dose adjustment required for renal impairment, hepatic impairment, body weight, sex, age, race, or ethnicity per the FDA label.
Missed dose: within 96 hours — take as soon as remembered. Beyond 96 hours — skip the dose and resume the weekly schedule to avoid accumulation.

Storage and handling

Mounjaro / Zepbound pens. Store refrigerated at 2–8 °C before first use. After first use, pens may be kept at room temperature up to 30 °C for the period specified on the FDA label. Do not freeze; discard if frozen. Protect from light; keep in the original carton until use.
Compounded vials. Handling depends on the preparing pharmacy. Compounded tirzepatide is typically reconstituted with bacteriostatic water (0.9% benzyl alcohol) or sterile water and stored refrigerated at 2–8 °C per the pharmacy's beyond-use date.
General. Avoid vigorous shaking (swirl to mix). Discard any solution that is cloudy, discolored, or contains particulates.

Reconstitution math (compounded vials)

Mounjaro and Zepbound pens deliver pre-measured weekly doses — users do not perform unit math. The worked examples below apply to compounded tirzepatide dispensed as a lyophilized powder in a vial.

Example 1 · 10 mg vial + 1 mL bac water concentration = 10 mg / 1 mL = 10 mg/mL = 10,000 mcg/mL
1 unit = 0.01 mL = 100 mcg = 0.1 mg
→ 2.5 mg = 25 units
→ 5 mg = 50 units
→ 7.5 mg = 75 units
→ 10 mg = 100 units (full syringe)

Example 2 · 30 mg vial + 1.5 mL bac water concentration = 30 mg / 1.5 mL = 20 mg/mL = 20,000 mcg/mL
1 unit = 0.01 mL = 200 mcg = 0.2 mg
→ 2.5 mg = 12.5 units
→ 5 mg = 25 units
→ 10 mg = 50 units
→ 15 mg = 75 units

Example 3 · 10 mg vial + 2 mL bac water concentration = 10 mg / 2 mL = 5 mg/mL = 5000 mcg/mL
1 unit = 0.01 mL = 50 mcg = 0.05 mg
→ 2.5 mg = 50 units
→ 5 mg = 100 units (full syringe)
→ 7.5 mg = 150 units (two draws)

As with every injectable peptide, "units" on an insulin syringe measures volume (0.01 mL each), not mass. The mg per unit is set entirely by your reconstitution concentration.

Frequently asked questions

What is the half-life of tirzepatide?

Approximately 5 days. Steady state is reached after about 4 weeks of once-weekly dosing.^[1][2]

How does it work?

Single peptide, dual agonist — activates both GIP and GLP-1 receptors. Produces insulin secretion, glucagon suppression, slowed gastric emptying, and central appetite effects.^[3]

What doses are FDA-approved?

Weekly: 2.5, 5, 7.5, 10, 12.5, 15 mg. Start at 2.5 mg for 4 weeks, then titrate per the FDA label.^[1]

How do I reconstitute a compounded vial?

At 10 mg/mL (10 mg + 1 mL bac water): 1 unit = 0.1 mg → 5 mg = 50 units. At 20 mg/mL (30 mg + 1.5 mL): 1 unit = 0.2 mg → 5 mg = 25 units. Commercial pens are pre-filled.

How many units equal 5 mg?

Depends on concentration. 10 mg/mL → 50 units. 20 mg/mL → 25 units. 5 mg/mL → 100 units (full syringe).

What if I miss a dose?

Within 4 days: take as soon as possible. Beyond 4 days: skip and resume the weekly schedule.^[1]

Primary references

U.S. Food and Drug Administration. MOUNJARO (tirzepatide) injection — full prescribing information. Updated label, 2025. accessdata.fda.gov — Mounjaro label
Furman BL, et al. Population pharmacokinetics of the GIP/GLP receptor agonist tirzepatide. Clin Pharmacokinet, 2024 (PMC10962491). PMC10962491
Farzam K, Patel P. Tirzepatide — StatPearls. NCBI Bookshelf (NBK585056). ncbi.nlm.nih.gov — StatPearls
U.S. Food and Drug Administration. ZEPBOUND (tirzepatide) injection — full prescribing information. 2024. accessdata.fda.gov — Zepbound label

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