How does a GLP-1 receptor agonist at 5 mg weekly compare on cost per milligram across routes?

Numbers first: a GLP-1 receptor agonist · 5 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?

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.

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

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.

Cost per milligram, adjusted honestly

The part that matters: 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.

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.

Start by listing every cost in the chain, since carriage, testing and wastage frequently exceed the difference in headline price.

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.

The underlying point is that 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.

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.

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.

The 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.

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.

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.

Larger orders reduce cost per milligram and increase exposure to a single lot, which is a real trade rather than a free win.

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