Tadalafil works by increasing blood flow to the penis during sexual stimulation, thereby helping men to achieve and maintain an erection. It achieves this by inhibiting the enzyme phosphodiesterase type 5 (PDE5), which is responsible for the breakdown of cyclic guanosine monophosphate (cGMP) in the smooth muscle cells of the penis. Increased levels of cGMP lead to relaxation of the smooth muscles and dilation of the blood vessels in the penis, allowing for improved blood flow and erection.