Catalyzes the oxidation of different tetrahydroprotoberberines, such as (S)-canadine, (S)-scoulerine and (S)-corypalmine (PubMed:3402447). Catalyzes the oxidation of (S)-coreximine and (S)-tetrahydropalmatine (PubMed:3402447, PubMed:21327819). Catalyzes the oxidation of different 1-benzylisoquinoline alkaloids, such as (S)-norreticuline, (S)-nororientaline, (S)-coclaurine and (S)-norisoorientaline (PubMed:3402447). Exhibits strict specificity for the (S)-enantiomer of tetrahydroprotoberbirines and 1-benzylisoquinoline alkaloids (PubMed:3402447). (S)-canadine + H(+) + 2 O2 = berberine + 2 H2O2 Binds 1 FAD per subunit in a bicovalent manner. Optimum pH is 8.9. The FAD cofactor is bound via a bicovalent 6-S-cysteinyl, 8alpha-N1-histidyl FAD linkage. Belongs to the oxygen-dependent FAD-linked oxidoreductase family.