What can the variability of strength be between different brands of supposedly identical medications?

Question

I remember reading that medications are within allowable specs if the contain +/- 30% of the labelled strength. I can't find the source of that information in order to check its validity.If that is the case, a 100mg pill would be considered to be within allowable tolerances if it has 70-130mg of the active ingredient.This could mean a 60% change in active ingredient if a patient switches from one brand to another, or if a manufacturer changes its manufacturing process.What is the allowed variability for prescription medications?

Answer 1

As far as I am aware, the rule of thumb or the maximum variability the FDA allows is +/- 10%. For instance, the expiration date is based upon the minimum time it will take o 10% of the medication to degrade.

Given the consistency with manufacturing these days, the actual margin for any drug is likely quite a bit smaller. With generics, they must prove what is called "bio-equivalence" to get approved. Which means releasing not only the same amount of drug, but pretty tightly to the time frame the original produces. (some drugs dump in all at once, some go in slowly) Whatever the original is, they have to match it.