Numbers first: a GLP-1 receptor agonist · 1.7 mg.
This should be a straightforward calculation and I keep getting two different answers.
The numbers are arbitrary; the method is what I am after.
Can someone walk through the arithmetic step by step?
1.7 mg a week is 88 mg a year and 7.4 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 88 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.
The relevant arithmetic is that a fifteen per cent price advantage disappears against a ten per cent content shortfall plus a testing cost.
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.
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.
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.
Divide by measured content, not by label claim. That is the whole correction.
edited 26 Apr 2026 by Dr_Ingrid_Baumgartner — clarified the distinction between purity and content
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsThe 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.
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.
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.
Fixed-needle syringes save more peptide than most price differences do.
Start by listing every cost in the chain, since carriage, testing and wastage frequently exceed the difference in headline price.
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.
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.
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.
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.
Syringe dead-space volumes are published per design, with fixed-needle insulin syringes under 5 microlitres and conventional luer designs at 35 microlitres or more.
The caveat is that optimising cost per milligram optimises for the wrong thing if documentation and consistency are what you actually need.
Larger orders are cheaper per milligram and concentrate lot risk. Price both.
Answer first: compare cost per milligram of measured peptide, not per milligram of label claim, because content varies enough to reverse a comparison.
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.
Include carriage and testing as per-milligram terms. They dominate small orders.
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