I have been reading about generics vs brand-name drugs. I've learned that generics go through extensive testing for bioequivalence (both rate of absorption and total absorption of the active ingredient). The statistical testing regime sounds pretty substantial to me, as far as testing of effectiveness goes.

Are generic drugs tested to ensure their risk of side effects will be roughly equivalent? Or, are there reasons to believe their side effects ought to be equivalent, in magnitude and likelihood? I understand that generics may have different inactive ingredients. Could this cause the risk of side effects to be materially different between versions of the same drug from two different manufacturers? Or is that super-unlikely? Should I discount/ignore concerns about the potential for variation in side effects between manufacturers?

(I do understand that there is a small risk that a patient is allergic to one particular inactive ingredient that's one formulation but not in another, but for purposes of this question, let's ignore that. Apart from that, could there be noticeable, reproducible differences? Or is this unlikely?)

(I have read What can the variability of strength be between different brands of supposedly identical medications?. I know enough statistics to understand why claims that "generics can be up to 45% different in effectiveness" are highly misleading. I've read about studies indicating that the average difference is more like 3% or so, and is probably similar to or smaller than the range of variation among different batches from the same manufacturer. But those seem to be measured by absorption into the blood, and I'm not sure what that implies for the risk of side effects.)

1 Answer 1


I'm going to assume you're referring to the United States and the FDA generic approval process.

FDA Abbreviated New Drug Application

For Abbreviated New Drug Applications (that they use for generic drugs) they are required to undergo bio equivalence testing as you said, but they:

are generally not required to include preclinical (animal) and clinical (human) data to establish safety and effectiveness.

This is because generic medications use the same active ingredient as the brand name equivalent. Chemically these substances are exactly the same. Since this is the chemical that got FDA approval as a drug, this is the chemical that was monitored for side effects and adverse reactions extensively in the original brand name drug application. Since this chemical is identical in both the brand and generic they expect no difference in side effects IF the dose exposure to the patient is the same. That is why most generic testing focuses on drug release, exposure, serum levels, etc. If they prove that the same chemical in their product is comparable in all of those aspects then it is assumed side effect profile will be comparable if not identical.

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