Tirzepatide Quick Start
Disclaimer
This page is an educational research and dosing reference. It is not medical advice and does not replace guidance from a licensed clinician. Tirzepatide carries a boxed warning for thyroid C-cell tumors. Tirzepatide is contraindicated in people with a personal or family history of medullary thyroid carcinoma or MEN 2.
Tirzepatide is a once-weekly injection that activates two appetite and blood-sugar hormones at the same time: GIP and GLP-1. The single-target competitor most people know is semaglutide (Ozempic, Wegovy), which only activates GLP-1. Retatrutide goes one step further by adding glucagon receptor activity, but it remains investigational. Tirzepatide activates both GIP and GLP-1, which is why it is called a dual agonist.
Mounjaro and Zepbound contain tirzepatide, but their prescribing instructions differ. Mounjaro is approved for type 2 diabetes from age 10 and to reduce major cardiovascular events in adults with type 2 diabetes at high risk. Zepbound is approved for adult weight reduction and long-term maintenance, and for moderate-to-severe obstructive sleep apnea (OSA) in adults with obesity. Use the label for the exact brand, indication, and age group.
Route
Subcutaneous (under-the-skin) injection, once per week, on the same day each week.
Dose ladder
Adult Zepbound example: 2.5 → 5 → 7.5 → 10 → 12.5 → 15 mg weekly. Later increases are optional, with at least 4 weeks at the current dose.
Measure
At an assumed 20 mg/mL, 1 mg equals 0.05 mL or 5 U-100 units. This is research-vial arithmetic, not a preparation or prescribing instruction.
Supplies
Research-vial supply totals are arithmetic only. Actual quantities depend on validated product-specific storage, discard dates, and losses.
Research status
FDA-approved drug as Mounjaro/Zepbound. Lyophilized research-use vials are a separate, non-FDA grey-market supply.
Mounjaro vs Zepbound at a glance
Tirzepatide labels by product and patient group (October 2026)
| Mounjaro | Zepbound | |
|---|---|---|
| Active drug | Tirzepatide | Tirzepatide |
| FDA indication | Type 2 diabetes from age 10; major cardiovascular-event risk reduction in high-risk adults with T2D | Adult weight reduction and long-term maintenance; moderate-to-severe OSA in adults with obesity |
| First approved | May 2022 | November 2023 |
| Dose selection | Start at 2.5 mg weekly; increase by 2.5 mg after at least 4 weeks if additional glycemic control is needed | 2.5 mg weekly for 4 weeks, then 5 mg; further 2.5 mg increases after at least 4 weeks as needed |
| Maintenance and maximum | Adult maximum 15 mg weekly; ages 10–17 maximum 10 mg weekly. Adult maintenance is not restricted to 5/10/15 mg | Weight: 5, 10, or 15 mg weekly. OSA: 10 or 15 mg weekly. Adult maximum 15 mg |
Sources: current Lilly Mounjaro and Zepbound prescribing information. Zepbound’s maintenance choices do not define Mounjaro dosing, and the adult maximum does not apply to pediatric Mounjaro use.
Tirzepatide Dosing Protocol & Schedule
The table below is an adult Zepbound example showing the earliest possible timing of each step. It is not a requirement to reach 15 mg. Zepbound starts at 2.5 mg weekly for 4 weeks, then 5 mg; later 2.5 mg increases may occur after at least 4 weeks at the current dose, based on response and tolerability. Weight-reduction maintenance is 5, 10, or 15 mg; OSA maintenance is 10 or 15 mg. The adult maximum is 15 mg weekly. Zepbound prescribing information, sections 2.1–2.2.
Tirzepatide Dosing Schedule
The first tab summarizes adult Zepbound labeling. The second is separate nominal research-vial arithmetic; it does not transfer an approved regimen to a research product.Adult Zepbound LabelResearch Vial (mg → units)
Earliest escalation example for adults prescribed Zepbound; later increases depend on clinical response and tolerability.
Adult Zepbound escalation example (earliest timing)
| Step | Earliest weeks | Weekly dose | Label context |
|---|---|---|---|
| Phase 1 — Initiation | Weeks 1–4 | 2.5 mg once weekly | Initiation dose; not an approved Zepbound maintenance dose. |
| Phase 2 — 5 mg step | Weeks 5–8 | 5 mg once weekly | Weight-reduction maintenance option; not an OSA maintenance dose. |
| Phase 3 — Mid escalation | Weeks 9–12 | 7.5 mg once weekly | Optional escalation step after at least 4 weeks at 5 mg. |
| Phase 4 — 10 mg step | Weeks 13–16 | 10 mg once weekly | Maintenance option for weight reduction and OSA. |
| Phase 5 — High escalation | Weeks 17–20 | 12.5 mg once weekly | Optional escalation step after at least 4 weeks at 10 mg. |
| Phase 6 — Maximum dose | Weeks 21+ | 15 mg once weekly | Adult maximum; maintenance option for weight reduction and OSA. |
Each increase after 5 mg is optional and requires at least 4 weeks at the current dose. Weight maintenance: 5/10/15 mg; OSA: 10/15 mg. Mounjaro has separate indication and age-specific guidance. These are prescribing-information examples, not research-vial instructions.
Missed dose
Per the Mounjaro and Zepbound prescribing information, if a dose is missed it should be administered as soon as possible within 4 days (96 hours). After that window, skip the missed dose and resume on the next regularly scheduled day. Do not double up.
Nominal mass-to-volume conversions only. Research powders are not established as equivalent to Mounjaro or Zepbound.
For an arithmetic example, a nominal 40 mg in a final 2.0 mL gives 20 mg/mL. The reference amounts below do not establish a human regimen, appropriate diluent, sterile preparation, or product equivalence. Research-grade powders are not FDA-approved medicines.
Mg → Units (40 mg vial + 2.0 mL BAC water = 20 mg/mL)
| Reference amount | Calculated volume | U-100 volume units |
|---|---|---|
| 2.5 mg | 0.125 mL | 12.5 units |
| 5 mg | 0.25 mL | 25 units |
| 7.5 mg | 0.375 mL | 37.5 units |
| 10 mg | 0.50 mL | 50 units |
| 12.5 mg | 0.625 mL | 62.5 units |
| 15 mg | 0.75 mL | 75 units |
At this concentration, the 12.5 mg and 15 mg calculated volumes exceed a 0.5 mL syringe. U-100 units measure volume, not drug potency; this table is not administration guidance.
Calculator
For any vial size or BAC-water volume, use the PepPal reconstitution calculator. Enter vial mg, water volume, and target dose to get exact syringe units.
Research-use only
Research-grade vials are sold for laboratory research, not for human use. An FDA-approved indication does not make a research-grade vial approved or suitable for treatment.
Tirzepatide weight-loss dose-tier guide
SURMOUNT-1 primary treatment-regimen results (obesity without diabetes, 72 weeks)
| Weekly dose | Average weight loss | Plain-English read |
|---|---|---|
| 5 mg | −15.0% | 5 mg assigned target; not a prediction for an individual. |
| 10 mg | −19.5% | 10 mg assigned target; not a required escalation step. |
| 15 mg | −20.9% | 15 mg assigned target; adult label maximum. |
Source: Jastreboff et al., NEJM 2022 (SURMOUNT-1), primary treatment-regimen estimand, which includes outcomes regardless of treatment discontinuation. These group averages do not determine an individual’s dose.
Steady state
Tirzepatide has a 5-day half-life. With weekly dosing, blood levels build up over about 4 weeks before stabilizing at roughly 1.6× a single dose. That is why each phase lasts at least 4 weeks, allowing the body time to adjust before a new dose’s effect can be judged.