Tadalafil works by increasing blood flow to the penis during sexual stimulation, which helps men to achieve and maintain an erection. It does this by inhibiting the enzyme phosphodiesterase type 5, which is responsible for the degradation of cyclic guanosine monophosphate (cGMP) in the corpus cavernosum of the penis. This leads to relaxation of smooth muscles and dilation of blood vessels in the penis, facilitating erection.