Table 1.

Characteristics of drugs for erectile dysfunction

Drug	Speed of onset of action	Duration of action
Sildenafil (Viagra)	30 to 40 minutes*	4 hours
Vardenafil (Levitra)	20 minutes	4 hours
Tadalafil (Cialis)	30 to 40 minutes	24 to 36 hours

^*Note: absorption of sildenafil is altered by consumption of food.