Phosphodiesterase type 5 inhibitors are competitive and reversible inhibitors. When a PDE5 inhibitor is used, it competitively binds to PDE5 to stop it from breaking down cGMP. PDE5 inhibitors are considered reversible because they bind to PDE5 for a limited amount of time. With the decrease in the levels of the cGMP, this will reverse the smooth muscle relaxation in the penis, which will end the erection.