Cost per milligram is the wrong denominator until you have adjusted for dead-space loss, content shortfall and the cost of the testing you will do. After that adjustment the ranking often changes.
Cost per milligram, worked honestly: a 10 mg vial at £34 is £3.40 per nominal milligram. If the content assay says 9.2 mg, that is £3.70 per actual milligram. If you then lose 4 µL of dead space per draw from a 2 mL fill across twenty draws, that is 80 µL or four per cent of the fill, taking you to £3.85. Add a £110 content assay amortised across the vial and it is £14.85 per milligram for the first vial of a new lot and £3.85 thereafter. The testing dominates, which is the actual argument for buying larger lots.
A defensible group-buy structure has three properties: the material is tested before it is split, the test is paid for from the pool rather than by the organiser, and the split is documented with photographs and a per-participant record of lot, volume and date. If any participant can reconstruct what they received from the records, a later dispute is resolvable. If not, it is not.
Independent testing costs have been stable enough over the past two years that amortisation arithmetic across a lot is worth doing before choosing a lot size, and the numbers usually favour a larger lot tested once over several small lots tested never.
The caveat is that none of this makes an unapproved product safe or lawful to use. It reduces one category of uncertainty — what is in the vial — and leaves every other category untouched.
Structure the group buy so that no single person is simultaneously the treasurer, the custodian and the arbiter. That one change removes most of the failure modes.
edited 22 Apr 2026 by Dr_Wren_Halliday — fixed an arithmetic slip in the third paragraph
6This matches what I was told by a laboratory, for whatever that is worth. – s_bhattacharya 7 months ago 5Minor: the trial name is hyphenated in the original publication. – aine_mulcahy 5 months ago add a comment