Tirzepatide “Dosing in Units” Means You’re Holding a Compounded Vial
Tirzepatide is a fully FDA-approved drug: Mounjaro for type 2 diabetes (2022) and Zepbound for weight management and obstructive sleep apnea (2023-2024). The reason people search for its dose 'in units', a 'reconstitution calculator', or 'BAC water' is that they are holding a compounded multi-dose vial, not the approved product. And since the FDA declared the tirzepatide shortage over, compounding it is generally no longer permitted.
Reviewed by the PepGuard team · Last reviewed Jul 28, 2026
Synthetic 39-amino-acid dual GIP and GLP-1 receptor agonist peptide, with a C20 fatty-diacid chain for once-weekly dosing · also called LY3298176, GIP and GLP-1 receptor agonist, Mounjaro, Zepbound
Photo: Haberdoedas / UnsplashThe approved drug, and the vial the search is about.
Tirzepatide is a 39-amino-acid peptide that activates both the GIP and GLP-1 receptors. As a molecule, it is fully FDA-approved: Mounjaro for type 2 diabetes (2022) and Zepbound for chronic weight management (2023) and obstructive sleep apnea (2024). Both come as a single-dose pen or a single-dose 0.5 mL vial at a fixed strength. You inject it once a week, as-is. There is nothing to reconstitute and nothing to measure “in units”.
So if you are searching for a tirzepatide unit conversion, a reconstitution calculator, bacteriostatic water, or a “20 mg/mL dosing chart”, you are not describing Mounjaro or Zepbound. You are describing a compounded or research-grade multi-dose vial — and that is the part of the picture that has changed the most. This page covers the approved dose schedule, how the “units” math works on a compounded vial, and why that vial is now, in almost all cases, not something a pharmacy can legally make.
The Mounjaro / Zepbound schedule.
| What's cited | Range |
|---|---|
| FDA-approved starting dose (Mounjaro / Zepbound) | 2.5 mg subcutaneously once weekly for 4 weeks |
| FDA-approved titration | Increase by 2.5 mg after at least 4 weeks; maintenance 5, 10, or 15 mg once weekly |
| FDA-approved maximum dose | 15 mg subcutaneously once weekly |
| How the approved product is supplied | Single-dose pen or single-dose 0.5 mL vial, fixed strength — not reconstituted, not dosed in syringe units |
| Compounded / grey-market multi-dose vial | No FDA-approved strength or protocol; 'units on a syringe', '20 mg/mL', and 'BAC water' apply only here |
The approved dose schedule below is for Mounjaro and Zepbound, which come as a single-dose pen or a single-dose 0.5 mL vial at a fixed strength. You do not reconstitute them and you do not measure them 'in units'. The only place a 'tirzepatide unit conversion' or 'BAC water calculator' applies is a compounded or research-grade multi-dose vial — which now sits outside the approval, with no verified strength and no standard protocol.
Why the approved product has no unit conversion.
A U-100 insulin syringe measures volume, scaled so that 100 units is 1 mL. That only helps you if you need to draw a variable volume from a multi-dose container. The approved tirzepatide products remove that step entirely: each pen or vial is one dose. A 5 mg Zepbound pen delivers 5 mg. There is no syringe, no draw volume, no unit count.
On a compounded vial, the conversion depends completely on the concentration the pharmacy chose. At 10 mg/mL, a 5 mg dose is 0.5 mL, which is 50 units. At 20 mg/mL, the same 5 mg is 0.25 mL, or 25 units. Neither concentration is an FDA strength, and the vial’s actual content is not verified by any regulator. If you want to see how concentration maps to syringe units in general, the peptide reconstitution chart lays out the arithmetic, and the calculator runs it for a specific vial.
What the trials found — for the approved drug.
Jastreboff et al., SURMOUNT-1, NEJM (2022): 2,539 adults with obesity (BMI ≥30, or ≥27 with a weight-related complication), no diabetes; randomized to tirzepatide 5, 10, or 15 mg weekly or placebo for 72 weeks. Mean weight change at week 72: -15.0% (5 mg), -19.5% (10 mg), -20.9% (15 mg) vs. -3.1% placebo. 50-57% of the 10-15 mg groups lost ≥20% of body weight, vs. 3% on placebo. Funded by Eli Lilly. Establishes the efficacy and safety of the approved product on a supervised titration — it does not validate a compounded vial's identity, strength, or purity.
Tirzepatide also carries a large type 2 diabetes trial program (SURPASS) behind the Mounjaro approval, and the Zepbound label adds trials in obstructive sleep apnea. The point that matters for this page: every one of those results is tied to the approved product on a supervised titration, not to a compounded vial.
Including the boxed warning.
The gastrointestinal effects come from the trials and label; the thyroid line is a boxed warning based on a rodent finding.
| Signal | Frequency | Context |
|---|---|---|
| Gastrointestinal (nausea, diarrhea, vomiting, constipation, abdominal pain, dyspepsia) | commonly reported | The most common adverse reactions in the Zepbound label and across the SURMOUNT and SURPASS trials; mostly mild-to-moderate and concentrated during dose escalation. |
| Injection-site reactions, hypersensitivity, fatigue, hair loss, eructation, GERD | occasionally reported | All listed at 5% or higher incidence in the Zepbound prescribing information. |
| Acute gallbladder disease and acute pancreatitis | occasionally reported | Both are described in the label's Warnings and Precautions; the label instructs discontinuation if pancreatitis is suspected. |
| Thyroid C-cell tumors | rarely reported | Boxed warning: tirzepatide causes thyroid C-cell tumors in rats; whether it does in humans is unknown. Contraindicated in anyone with a personal or family history of medullary thyroid carcinoma or MEN 2. |
| Identity, strength, and purity of a compounded or grey-market vial | unknown / not studied | A compounded multi-dose vial is not the product studied in the trials. There is no regulatory mechanism confirming it contains tirzepatide, at the labeled strength, free of impurities. |
Compounded tirzepatide had a deadline, and it has passed.
Tirzepatide the molecule has full FDA approval — as Mounjaro (type 2 diabetes, 2022) and Zepbound (chronic weight management, 2023; obstructive sleep apnea, 2024), both from Eli Lilly. Compounded tirzepatide existed only because the drug was in shortage from 2022, which temporarily allowed pharmacies to make copies. That window has closed. The FDA first announced the shortage resolved on October 2, 2024, then issued a formal declaratory order re-confirming it on December 19, 2024. That order set hard deadlines: state-licensed 503A pharmacies had to stop compounding, distributing, and dispensing tirzepatide injection by February 18, 2025, and 503B outsourcing facilities by March 19, 2025. The FDA has since stated plainly that "tirzepatide and semaglutide do not currently appear on the 503B bulks list or on FDA's drug shortage list" — meaning neither compounding pathway is open for it. A 503A pharmacy can still compound a product that is 'essentially a copy' of an approved drug only if a prescriber documents a clinically significant difference for a specific patient, or within a narrow tolerance of four or fewer prescriptions per calendar month. Selling compounded tirzepatide as a routine cash-pay weight-loss product is not that, and the FDA has been sending warning letters over it.
Tirzepatide is not retatrutide
Tirzepatide is an approved dual GIP/GLP-1 agonist. Retatrutide is an investigational triple agonist with no approval at all. They are frequently cross-shopped online, but only one of them has an FDA-approved product behind it.
Every claim above, traced back.
The FDA-approved label, the SURMOUNT-1 trial and its registration, the FDA’s declaratory order and compounding-policy statement, and Drugs@FDA. Click through and check them yourself.
Tirzepatide questions, answered.
Generally, no. Compounded tirzepatide was only permitted because the drug was in shortage. The FDA declared that shortage resolved — first on October 2, 2024, then re-confirmed in a formal declaratory order on December 19, 2024 — and set deadlines: 503A pharmacies had to stop by February 18, 2025 and 503B outsourcing facilities by March 19, 2025. The FDA has stated that tirzepatide does not appear on the 503B bulks list or the drug shortage list, so neither compounding route is open. A pharmacy can still compound a version only if a prescriber documents a clinically significant difference for an individual patient, or under a narrow four-or-fewer-prescriptions-per-month tolerance. A routine cash-pay compounded weight-loss vial is neither.
Not the approved product. Mounjaro and Zepbound come as a single-dose pen or a single-dose 0.5 mL vial, already in solution, at a fixed strength — you inject it as-is, once a week. The only tirzepatide that gets reconstituted from a powder with bacteriostatic water is a compounded or research-grade multi-dose vial, which is exactly the material that now sits outside the FDA approval.
There is no fixed answer, because the approved product is not dosed in units at all. On a compounded vial, it depends entirely on the concentration the pharmacy made: at 10 mg/mL, 5 mg is 0.5 mL, which is 50 units on a U-100 insulin syringe; at 20 mg/mL, the same 5 mg is 0.25 mL, or 25 units. The concentration is whatever the compounder chose, which is one more reason a compounded vial is not equivalent to the approved pen. See the reconstitution chart for how concentration maps to units.
For the approved products (Mounjaro and Zepbound): start at 2.5 mg subcutaneously once weekly for 4 weeks, then increase to 5 mg once weekly. After that, the dose can be increased in 2.5 mg steps, with at least 4 weeks between increases, to a maintenance dose of 5, 10, or 15 mg once weekly. The maximum approved dose is 15 mg once weekly. This is a physician-directed schedule with a specific product, not a template for a compounded vial.
It is a compounded-pharmacy concentration, not an FDA product. The approved Zepbound and Mounjaro presentations are single-dose, expressed as milligrams per 0.5 mL (for example 5 mg/0.5 mL), not as a multi-dose 'mg/mL' vial. A '20 mg/mL' or '10 mg/mL' vial with a dosing chart is compounded or research-grade material, and its actual content is not verified by any regulator.
Tirzepatide is the active ingredient in both. Mounjaro is approved for type 2 diabetes (2022); Zepbound is approved for chronic weight management (2023) and moderate-to-severe obstructive sleep apnea with obesity (2024). Both are Eli Lilly products and both deliver tirzepatide in a single-dose pen or vial. 'Compounded tirzepatide' contains the same molecule name but is not either of these approved products.
In SURMOUNT-1 (NEJM 2022, 2,539 adults with obesity, 72 weeks), once-weekly tirzepatide produced mean weight reductions of 15.0% at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg, versus 3.1% with placebo. Between 85% and 91% of participants on tirzepatide lost at least 5% of body weight. Those results are for the approved drug given under trial supervision, not a forecast for an individual using a compounded vial.
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