In people who are deficient in CYP2D6, coadministration of modafinil with substrates of CYP2D6 which have ancillary routes of elimination via CYP2C19 (eg, tricyclic antidepressants and selective serotonin reuptake inhibitors) may result in elevated circulating levels of these medicines and involve dose adjustment (Robertson et al 2000; PROVIGIL® 2