The specifics, since they change the answer: tirzepatide · 5 mg.
I would rather understand the derivation than memorise the outcome.
Two people I asked gave two answers that differ by a factor of ten, which is suggestive.
Can someone walk through the arithmetic step by step?
5 mg a week is 260 mg a year and 21.7 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 260 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.
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.
| Step | Value | Note |
|---|---|---|
| Vial price, 10 mg nominal | £34.00 | As advertised |
| Nominal cost per mg | £3.40 | 34 ÷ 10 |
| Measured content | 9.2 mg | Independent content assay |
| Cost per actual mg | £3.70 | 34 ÷ 9.2 |
| Dead-space loss, 20 draws | 4 % | 80 µL of a 2 mL fill |
| Cost per delivered mg | £3.85 | 3.70 ÷ 0.96 |
| First vial, with £110 assay | £14.85 | Testing dominates a single vial |
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.
Carriage on international consignments scales sub-linearly with weight, which is the quantitative basis for order consolidation.
Fixed-needle syringes save more peptide than most price differences do.
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsThe short version: unit price, carriage, testing, dead-space loss and wastage. The first is the one everybody compares and rarely the one that decides it.
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.
Concretely, 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.
The relevant arithmetic is that a fifteen per cent price advantage disappears against a ten per cent content shortfall plus a testing cost.
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.
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.
Divide by measured content, not by label claim. That is the whole correction.
The relevant detail is that 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.
Decide whether you are optimising cost or confidence before you build the model.
edited 30 Nov 2025 by grainne_ahearn — updated for the 2026 guidance change
Wastage from expired reconstituted vials is a real line item and nobody includes it.
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.
Include carriage and testing as per-milligram terms. They dominate small orders.
edited 13 Mar 2026 by u100_marks — reworded for clarity after a comment
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.