The fact that this is even a consideration is scary, and frankly, what the book was apparently about. I always believed generics were identical.

What I’ve heard anecdotally: The “generic” part of a generic drug is the active ingredient - that should be essentially the same between manufacturers. What differs, however, is the delivery mechanism. So for something that is extended release, the mechanism for releasing over time can vary between manufacturer.

I’m not entirely sure that this is the full story though, I haven’t researched the problem enough.

The pharmacy will change drug distributors, which will change the manufacturer supplying their inventory.

I don’t. I get a different manufacturer every few months.