Sildenafil is the active ingredient in Viagra®. Sildenafil is a medicine used for erectile dysfunction. It aids in producing an erection when you are sexually excited. Sildenafil causes erections only during sexual excitement. It does not work in the absence of arousal.
Tadalafil is the active ingredient in in Cialis®. Tadalafilis is a medicine used to treat men with erectile dysfunction, benign prostatic hyperplasia (enlargement of the prostate gland, which may in turn block the flow of urine), or both.
Vardenafil is the active ingredient in Levitra®. Vardenafil works by relaxing blood vessels in the penis, thereby increasing blood flow to the penis to help improve erectile function and keep an erection satisfactory for sexual activity.