Catalyzes C14-demethylation of lanosterol; it transforms lanosterol into 4,4'-dimethyl cholesta-8,14,24-triene-3-beta-ol. a 14alpha-methyl steroid + 3 O2 + 3 reduced [NADPH--hemoprotein reductase] = a Delta(14) steroid + formate + 4 H(+) + 4 H2O + 3 oxidized [NADPH--hemoprotein reductase] Inhibited by ketoconazole. May also be inhibited to a lesser extent by propiconazole. Steroid biosynthesis; zymosterol biosynthesis; zymosterol from lanosterol: step 1/6. Strongly expressed in intestine. Moderately expressed in liver, with higher levels in females compared to males. Also detected at low levels in brain, eye, kidney and testis. Belongs to the cytochrome P450 family.