All three drugs–sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis)–belong to a class of medications called phosphodiesterase-5 (PDE5) inhibitors. They work by increasing blood flow to the penis, facilitating an erection. However, subtle differences exist in their mechanisms.
Sildenafil (Viagra)
Sildenafil selectively inhibits PDE5, an enzyme that breaks down cyclic GMP (cGMP). Higher cGMP levels relax the smooth muscles in the penis’ blood vessels, allowing increased blood flow. This effect is triggered by sexual stimulation; sildenafil doesn’t cause erections independently. Its effects typically last 4-5 hours.
Vardenafil (Levitra)
Vardenafil also inhibits PDE5, leading to elevated cGMP and improved blood flow to the penis. It’s considered to have a faster onset of action than sildenafil, but similar duration of effect, around 4-5 hours. Its higher potency means a lower dose might suffice for some individuals.
Tadalafil (Cialis)
Tadalafil, like the others, blocks PDE5. Its key distinction lies in its significantly longer duration of action–up to 36 hours, earning it the nickname “the weekend pill”. This prolonged effect stems from tadalafil’s slower metabolism and longer half-life compared to sildenafil and vardenafil. The mechanism remains the same: increased cGMP and blood flow to the penis following sexual stimulation.
