> Twelve of the 14 drug compounds tested (86%) were present in concentrations at least 90% of the labeled amounts, the generally recognized minimum acceptable potency. Three of these compounds were present at greater than 110% of the labeled content. Two compounds (aspirin and amphetamine) were present in amounts of less than 90% of labeled content. One compound (phenacetin) was present at greater than 90% of labeled amounts from 1 medication tested, but less than 90% in another medication that contained that drug.
My brother-in-law works in pharma manufacturing, this stuff is really hard and it's basically impossible to create exactly identical pills, apparently in large part because the active ingredient is frequently <1% of the volume of the pill. The best they can do is control the range of dosage in pills, and there's variance in what that range is across drugs (i.e. some compounds can't be spray dried, can't be heated hot enough to make binders liquid, etc).
Depending on necessity and value they can typically engineer more precision, but it gets very expensive very fast.
> Twelve of the 14 drug compounds tested (86%) were present in concentrations at least 90% of the labeled amounts, the generally recognized minimum acceptable potency. Three of these compounds were present at greater than 110% of the labeled content. Two compounds (aspirin and amphetamine) were present in amounts of less than 90% of labeled content. One compound (phenacetin) was present at greater than 90% of labeled amounts from 1 medication tested, but less than 90% in another medication that contained that drug.
http://jamanetwork.com/journals/jamainternalmedicine/fullart...
Sounds like maybe concentrations are allowed to vary a bit from the label at manufacturing time? Not sure, maybe someone who knows more can comment.