Phosphodiesterase-5 inhibitors, such as sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra), have revolutionized the treatment of erection problems (erectile dysfunction). But they can cause life-threatening side effects for anyone who also takes nitroglycerin or another medicine containing an organic nitrate. This combination can make your blood pressure fall too low, possibly leading to a stroke, a heart attack, or death. Do not take nitrate-containing medicines up to 24 hours after you take sildenafil (Viagra) or vardenafil (Levitra), or up to 48 hours after you take tadalafil (Cialis).

Medicines that contain organic nitrates include:

• Nitroglycerin (such as Minitran, Nitro-Dur, Nitrolingual Pumpspray, Nitrostat).
• Isosorbide mononitrate (such as ISMO, Monoket).
• Isosorbide dinitrate (such as Dilatrate-SR, Isordil).
• Sodium nitroprusside (such as Nitropress).
• Amyl nitrite or amyl nitrate (sometimes called "poppers"), which are sometimes abused.

Nitrates found in foods are not a danger when taking phosphodiesterase-5 inhibitors.