[thatcat]

Presumably because patented drugs don't have any bioequivalent drugs to compare to and the margin of error is based off of how different the generic is from the original. Originals do have stricter regulations on the amounts of inactive fillers used though.

> Most regulators worldwide have decided that a 20% variation is generally not clinically significant.

>Two versions of a drug are generally said to be bioequivalent if the 90% confidence intervals for the ratios of the geometric means (brand vs. generic) of the AUC and Cmax fall within 80% and 125%. The tmax (brand vs. generic) must also be comparable — and there should not be any significant differences between different patients.

[1]https://www.sciencebasedmedicine.org/generic-drugs-are-they-...

[2](cmax, auc, graph comparison) http://www.bpac.org.nz/BPJ/2007/March/bioequiv.aspx