- Taking any of the following medications within the six weeks prior to the start of the study: imipramine, amitriptyline, doxepin, nortriptyline, maprotiline, chlorpromazine, clozapine, foscarnet, ganciclovir, ritonavir, theophylline, calcium channel blockers, beta blockers, tadalafil, vardenafil, avanafil, and sildenafil;