In people who are deficient in CYP2D6, coadministration of modafinil with substrates of CYP2D6 that have ancillary routes of elimination by way of CYP2C19 (eg, tricyclic antidepressants and selective serotonin reuptake inhibitors) might bring about elevated circulating levels of these medicines and call for dose adjustment (Robertson et al 2000; PR