Catalyzes the formation of thebaine from (7S)-salutaridinol 7-O-acetate at the expense of labile hydroxylated by-products, which are preferentially produced by spontaneous allylic elimination. No visible activity toward (7S)-salutaridinol (at pH 7). (7S)-O-acetylsalutaridinol = acetate + H(+) + thebaine Slightly inhibited by salutaridine and (7S)-salutaridinol. Optimum pH is 8. Alkaloid biosynthesis; morphine biosynthesis. Homodimer (allosteric) and oligomers. Expressed in poppy latex. Plants lacking both THS1 and THS2 exhibit reduced thebaine levels but accumulation of the upstream intermediates salutaridinol and reticuline. Can be used to improve thebaine yield in engineered yeast. Belongs to the MLP family.