Mechanism of action
Sildenafil induces erections in response to sexual stimulation by causing smooth muscle relaxation in the corpus cavernosum through selective inhibition of phosphodiesterase type 5 (PDE5). Since sildenafil only lowers the inactivation of cyclic guanosine monophosphate (cGMP) and does not enhance its production, penile erection due to sildenafil is achieved only in response to sexual stimulation.