Many tricyclic antidepressants metabolized by CYP2D6 would be here, if you put the nonmetabolizers up against the rapid metabolizer, https://en.wikipedia.org/wiki/Doxepin for example.
I'm surprised the article didn't mention anything about pharmacogenetics. For example, drug-metabolizing enzyme polymorphisms can often lead to a 10+ fold difference in Cmax (or name the parameter) between a poor and an ultrarapid metabolizer of some enzyme.