Drug interaction with P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) may influence its tissue disposition including blood–brain barrier transport and result in potent drug–drug interactions. The limited data obtained using in-vitro models indicate that methadone, buprenorphine, and cannabinoids may interact with human P-gp; but almost nothing is known about drugs of abuse and BCRP. We used in vitro P-gp and BCRP inhibition flow cytometric assays with hMDR1- and hBCRP-transfected HEK293 cells to test 14 compounds or metabolites frequently involved in addiction, including buprenorphine, norbuprenorphine, methadone, ibogaine, cocaine, cocaethylene, amphetamine, N-methyl-3,4-methylenedioxyamphetamine, 3,4-methylenedioxyamphetamine, nicotine, ketamine, Δ9-tetrahydrocannabinol (THC), naloxone, and morphine. Drugs that in vitro inhibited P-gp or BCRP were tested in hMDR1- and hBCRP-MDCKII bidirectional transport studies. Human P-gp was significantly inhibited in a concentration-dependent manner by norbuprenorphine>buprenorphine>methadone>ibogaine and THC. Similarly, BCRP was inhibited by buprenorphine>norbuprenorphine>ibogaine and THC. None of the other tested compounds inhibited either transporter, even at high concentration (100 µm). Norbuprenorphine (transport efflux ratio ∼11) and methadone (transport efflux ratio ∼1.9) transport was P-gp-mediated; however, with no significant stereo-selectivity regarding methadone enantiomers. BCRP did not transport any of the tested compounds. However, the clinical significance of the interaction of norbuprenorphine with P-gp remains to be evaluated.