How does tirzepatide at 15 mg weekly compare on cost per milligram across routes?

The particulars: tirzepatide · 15 mg.

I would like the arithmetic checked rather than the conclusion asserted.

I have deliberately not used an online calculator because I want to be able to check the result.

Can someone show the working rather than just the answer?

15 mg a week is 780 mg a year and 65 mg in an average month — put every route on that denominator before comparing anything. Cost per milligram is the only figure that survives the comparison, because the presentations differ: a licensed pen prices a dose, a compounding pharmacy prices a vial, and a research supplier prices a mass. Divide each one's twelve-month cost by 780 mg and the three become the same number in the same unit. Then add what the cheapest route does not include — independent purity and content testing, the vials you discard, and the postage — because a route that needs testing to be trustworthy has that testing in its cost per milligram whether you account for it or not.

Answer first: compare cost per milligram of measured peptide, not per milligram of label claim, because content varies enough to reverse a comparison.

The full calculation: (unit price + carriage share + testing share) ÷ (nominal mg × measured content fraction × (1 − dead-space and wastage fraction)). Every term after the first is routinely omitted.

Change one number and it reverses: if B assays at 82 per cent, that is 8.2 mg for £52, or £6.34/mg, and the cheaper vial is now the more expensive peptide.

Published content assay results across the independent services show nominal and measured content differing by one to ten per cent, which is the term that makes label-price comparisons unreliable.

Fixed-needle syringes save more peptide than most price differences do.

The relevant arithmetic is that a fifteen per cent price advantage disappears against a ten per cent content shortfall plus a testing cost.

Worked example. Supplier A: £60 for a 10 mg vial, content 96 per cent, so 9.6 mg for £60, or £6.25/mg before carriage. Supplier B: £52 for the same nominal vial, content 88 per cent, so 8.8 mg for £52, or £5.91/mg. B still wins here, but the gap has narrowed from thirteen per cent on the label to five per cent in reality.

Independent testing costs roughly the price of one to two vials at the services this community uses. On a two-vial order that is a fifty to a hundred per cent surcharge; on a twenty-vial order it is five per cent.

Independent testing prices at the services this community uses are published and are stable enough to model.

Larger orders are cheaper per milligram and concentrate lot risk. Price both.

Answering this needs the order size, because carriage and testing amortise very differently across one vial and across ten.

Cost per milligram is the wrong metric entirely if you are optimising for confidence rather than price, and it is worth saying which one you are doing before you build the spreadsheet.

The relevant detail is that dead-space loss is small with fixed-needle insulin syringes — a few microlitres per draw — and substantial with detachable-needle luer syringes at 35 to 100 microlitres. Across twenty draws that is up to two millilitres of solution.

Carriage on international consignments scales sub-linearly with weight, which is the quantitative basis for order consolidation.

Divide by measured content, not by label claim. That is the whole correction.

Testing cost per milligram falls sharply with order size, which is the main argument against very small repeat orders.

Wastage from a reconstituted vial discarded at the end of its in-use period is a genuine cost, and it is a function of the diluent volume chosen at reconstitution rather than of anything the supplier did.

The caveat is that optimising cost per milligram optimises for the wrong thing if documentation and consistency are what you actually need.

Decide whether you are optimising cost or confidence before you build the model.

The honest answer is that the cheapest headline price is frequently not the cheapest outcome.

Carriage amortises across the order. Twenty-five pounds of carriage on one vial is £2.50/mg on a 10 mg vial; on ten vials it is £0.25/mg. That single term explains most of the case for larger, less frequent orders.

A spreadsheet built on label claim rather than measured content is precise about the wrong number.

Include carriage and testing as per-milligram terms. They dominate small orders.