Potentiated antihypertensive effect w/ other vasodilators, antihypertensives, β-blockers, Ca antagonists, neuroleptics or TCAs, alcohol. Enhanced hypotensive effect w/ certain drugs (phosphodiesterase inhibitors) for erectile dysfunction or pulmonary arterial HTN. Patients previously treated w/ organic nitrates (eg, isosorbide dinitrate, isosorbide-5-mononitrate) may require increase in glyceryl trinitrate dose to achieve desired effect. Enhanced hypertensive effect of dihydroergotamine. Weakened effect of heparin.