Guide
Retatrutide Vial Sizes: Formats, Comparisons, and Reconstitution
A 10 mg retatrutide vial runs $10.00/mg and a 20 mg vial $9.75/mg as of September 2026, with mcg-per-unit math for 1, 2, and 3 mL fills.
- retatrutide
- vial-sizes
- reconstitution
- pricing
Two retatrutide vial sizes carry prices in the catalog this register tracks: 10 mg at $100 and 20 mg at $195, as of September 2026. Dividing price by vial mass gives $10.00/mg and $9.75/mg, so the 20 mg format costs 2.5% less per milligram. The mg figure on the label states total lyophilized mass and nothing else. Concentration appears only after bacteriostatic water is added: 10 mg in 2 mL is 5 mg/mL, and 20 mg in the same 2 mL is 10 mg/mL.
Is the 20 mg Retatrutide Vial Cheaper Per mg?
Yes, by $0.25/mg, which is a smaller gap than the doubled vial mass suggests.
| Vial format | Catalog price (USD) | Price ÷ mg | Cost of 20 mg in this format |
|---|---|---|---|
| 10 mg | $100 | $10.00/mg | $200 (two vials) |
| 20 mg | $195 | $9.75/mg | $195 (one vial) |
Caption: catalog prices for the two retatrutide vial sizes tracked by this register, as of September 2026; the per-mg and two-vial columns are arithmetic on those prices (100 ÷ 10, 195 ÷ 20, 100 × 2).
Buying 20 mg as two 10 mg vials costs $200 against $195 for the single 20 mg vial, a $5 spread on the same total mass. The 2.5% discount comes from $0.25 ÷ $10.00. Vial glass, stopper, and shipping do not double when fill mass doubles, which is the usual reason a larger format prices below linear.
The tradeoff runs the other way on flexibility. Two 10 mg vials can be reconstituted at two different volumes, on two different dates, with the second left sealed; one 20 mg vial commits the whole mass to a single diluent volume at a single point in time. Whether that $5 is worth spending is a question about how much solution sits unused, which the register handles in its single-dose versus multi-dose format notes rather than in the price column.
How Much Water Goes Into Each Vial Size?
Concentration follows one relationship: mg/mL equals vial mass in mg divided by mL of bacteriostatic water added. On a U-100 insulin syringe, 1 mL is 100 units, so each unit is 0.01 mL, and mcg per unit equals mg/mL multiplied by 10 (1 mg = 1000 mcg, divided across 100 units).
| Diluent added (mL) | 10 mg vial: mg/mL | 10 mg vial: mcg/unit | 20 mg vial: mg/mL | 20 mg vial: mcg/unit |
|---|---|---|---|---|
| 1 | 10.0 | 100 | 20.0 | 200 |
| 2 | 5.0 | 50 | 10.0 | 100 |
| 3 | 3.33 | 33.3 | 6.67 | 66.7 |
Caption: concentration and per-unit mass for both catalog retatrutide vial sizes at three common fill volumes; every cell is arithmetic on the vial mg and the mL in column one, with no external figure involved.
Working one row in full: a 20 mg vial with 2 mL of bacteriostatic water gives 20 ÷ 2 = 10 mg/mL, which is 10,000 mcg/mL. One syringe unit holds 0.01 mL, so 0.01 × 10,000 = 100 mcg per unit. Checking the same result a second way, the full 2 mL contains 20,000 mcg spread over 200 unit marks (2 mL ÷ 0.01 mL), and 20,000 ÷ 200 = 100 mcg per unit.
Total unit count depends on volume alone, not on vial size. Both a 10 mg and a 20 mg vial filled to 2 mL yield 200 units of solution; the 20 mg vial simply puts twice the mass behind each mark. That is the single fact that makes cross-listing comparison fail when the fill volume is missing, and it is why choosing a fill volume for a given format is a separate decision from choosing the format.
Which mg Totals Do the Retatrutide Trials Use?
Published phase 2 work used weekly subcutaneous mg amounts in the low single digits to low teens, which is the range that makes a 10 mg or 20 mg vial a sensible unit of packaging in the first place.
| Weekly mg | Obesity phase 2, 24-week body weight, n=338 (NEJM 2023 phase 2 trial) | T2D substudy, 36-week total fat mass, n=189 (Lancet Diabetes Endocrinol 2025 body-composition substudy) |
|---|---|---|
| 0.5 | not in this trial | −4.9% (SE 1.4) |
| 1 | −7.2% | not in this trial |
| 4 | −12.9% (combined arms) | −15.2% (SE 3.2, pooled) |
| 8 | −17.3% (combined arms) | −26.1% (SE 2.5, pooled) |
| 12 | −17.5% | −23.2% (SE 3.0) |
| placebo | −1.6% | not reported in the retrieved record |
Caption: dose arms and primary results from two separate phase 2 retatrutide studies. Column two is least-squares mean percent change in body weight at 24 weeks in 338 adults over a 48-week trial; column three is percent change in total fat mass by DXA at week 36 in the 189-participant body-composition substudy of a 281-participant trial registered as NCT04867785.
The two columns disagree on where the curve flattens, and the disagreement is worth stating rather than smoothing. In the obesity trial the 8 mg and 12 mg arms landed 0.2 percentage points apart at 24 weeks (−17.3% and −17.5%), while in the type 2 diabetes substudy the 8 mg pooled arm showed a larger fat-mass reduction than the 12 mg arm (−26.1% against −23.2%). These are different populations, different endpoints, and different timepoints, so the comparison is descriptive only.
Neither figure is a property of the vial. A vial holds mass; the trials divided that mass into weekly increments. Dividing catalog vial mass by the weekly mg of an arm gives 10 ÷ 4 = 2.5 weekly increments from a 10 mg vial at the 4 mg arm, or 20 ÷ 8 = 2.5 from a 20 mg vial at the 8 mg arm. These figures are compiled for research reference only.
What Does a 24-Week mg Total Cost in Each Format?
Take the 4 mg weekly arm of the phase 2 obesity trial over its 24-week primary endpoint window: 4 mg × 24 weeks = 96 mg of total mass.
| Format | Vials needed for 96 mg | Total cost (Sept 2026 prices) | Effective $/mg over 96 mg | Mass left over |
|---|---|---|---|---|
| 10 mg | 10 (96 ÷ 10 = 9.6, rounded up) | $1,000 | $10.42 | 4 mg |
| 20 mg | 5 (96 ÷ 20 = 4.8, rounded up) | $975 | $10.16 | 4 mg |
Caption: cost of assembling a 96 mg total from each catalog retatrutide vial size, using September 2026 prices of $100 and $195; effective per-mg is total cost ÷ 96 (1000 ÷ 96 = 10.4167, 975 ÷ 96 = 10.1563).
Both formats leave the same 4 mg unused because both round to 100 mg purchased, so the entire difference is the $25 between $1,000 and $975. Effective per-mg cost sits above the headline $10.00 and $9.75 in both rows for the same reason: vials are indivisible, and 96 is not a multiple of either 10 or 20.
The gap widens with volume. At the 8 mg arm the same 24 weeks needs 192 mg, which is 20 ten-mg vials ($2,000) or 10 twenty-mg vials ($1,950), a $50 spread. Anyone reconciling a listing’s quoted per-mg claim against its actual invoice should run the rounding step, since a vendor quoting $9.75/mg is quoting the unrounded figure.
Why Do Listings Show Sizes the Catalog Doesn’t?
Vendor listings quote formats outside the two priced above, and the register keeps those on separate pages because the per-mg arithmetic has to be rebuilt from each listing’s own price and mg figure. The 5 mg against 10 mg breakdown covers the smaller end of that spread, where fixed packaging cost is spread over the least mass and per-mg pricing is usually worst.
Format availability also moves independently of price. A size can be listed, priced, and out of stock at the same time, which is why this register dates every revision instead of treating a catalog snapshot as permanent.
A 20 mg vial reconstituted at 2 mL sits at 10 mg/mL and yields 200 units of solution that then carries a shelf life, which is a storage question rather than a format one. The register tracks that separately in its notes on refrigerated storage after mixing.