An NADPH-dependent P450 enzyme that plays an essential role in the sterol biosynthetic pathway by catalyzing the demethylation of 14-methyl sterols such as lanosterol. The enzyme acts via the repeated hydroxylation of the 14-methyl group, resulting in its stepwise conversion into an alcohol, an aldehyde and then a carboxylate, which is removed as formic acid. sterol 14-demethylase is an unusual cytochrome P450 enzyme in that it is found in a broad variety of organisms including animals; plants; fungi; and protozoa.