The use of a drug for which the major clearance mechanism in humans is CYP2D6 mediated oxidative biotransformation selected from the group consisting of NMDA receptor antagonist containing a primary, secondary or tertiary alkylamine moiety and a neurokinin-1 (NK-1) receptor antagonist containing a primary, secondary or tertiary alkylamine moiety; and a CYP2D6 inhibitor in the manufacture of a medicament for the treatment of a human in need thereof wherein the drug and the inhibitor are not the same compound. The said drug for which the major clearance mechanism in humans is CYP2D6 mediated oxidative biotransformation may be further selected from the group consisting of mequitazine, tamsulosin, oxybutynin, ritonavir, iloperidone, ibogaine, delavirdine, tolteridine, promethazine, pimozide, epinastine, tramodol, procainamide, methamphetamine, tamoxifen, nicergoline, fluoxetine, alprenolol, amiflamine, amitriptyline, aprindine, brofaromine, buturalol, cinnarizine, clomipramine, codeine, debrisoquine, desipramine, desmethylcitalopram, dexfenfluramine, dextromethorphan, dihydrocodine, dolasetron, encainide, ethylmorphine, flecainide, flunarizine, fluvoxamine, guanoxan, haloperidol, hydrocodone, indoramine, imipramine, maprotiline, methoxyamphetamine, methoxyphenamine, methylenedioxymethamphetamine, metoprolol, mexiletine, mianserin, minaprine, procodeine, nortriptyline, N-propylajmaline, ondansetron, oxycodone, paroxetine, perhexiline, perphenazine, phenformine, promethazine, propafenone, propanolol, risperidone, sparteine, thioridazine, timolol, tomoxetine, tropisetron, venlafaxine or zuclopenthixol; and wherein the CYP2D6 inhibitor may be selected from the group consisting of quinidine, ajmalacine, sertraline, venlafaxine, dexmedetomidine, tripennelamine, premethazine, hydroxyzine, halofrintane, chloroquine, moclobemide or St John's wort.
Use of CYP2D6 inhibitors in combination therapies