CYP2C19 er genstand for genetisk polymorfisme, og 2- 6% af befolkningen, der har en ringe metaboliseringsevne, er homozygoter for en mutant CYP2C19- allel og mangler derfor et funktionelt CYP2C19- enzym.
CYP2C19 is subject to genetic polymorphism and 2-6% of the population, called poor metabolisers (PMs), are homozygote for a mutant CYP2C19 allele and therefore lacks a functional CYP2C19 enzyme.