Price per Milligram

Price per milligram is the arithmetic of dividing what a buyer pays by the mass of active substance the label claims, giving a currency figure per milligram. It is the dominant comparison metric in informal peptide markets because it is the only number that is always available. As a way of ranking two vials of the same well-characterised substance from equally controlled sources it is reasonable. As a way of ranking anything else it silently assumes three things that are frequently untrue: that the labelled mass is present, that the mass is the peptide rather than everything in the vial, and that a milligram of one compound is comparable to a milligram of another.

The mass assumption fails in ordinary chemistry before anyone is dishonest. Lyophilised peptide contains counterion, residual water and process salts, so gross mass exceeds peptide mass; a trifluoroacetate salt of a basic peptide can carry a double-digit percentage of the powder weight as counterion, and net peptide content is what a quantitative assay reports, not what the vial weighs. Chromatographic purity expressed as area percent is a separate quantity again, and neither figure establishes identity.

The potency assumption fails across molecules. Milligram-for-milligram comparison between compounds with different receptor affinities and different clearance is a category error, not a bargain, and cheapness in these markets is usually explained by what has been omitted: release testing, sterility and endotoxin control, cold chain, and documented provenance.

Where it bites hardest is in the inference that a low figure indicates efficient supply. More often it prices out a crude synthesis, a short or deleted sequence fraction, or an underfilled vial. A price per milligram is a claim about a label, and a label is exactly what is unverified in an unregulated channel.