The Megalis contains tadalafil, which is a potent PDE5 inhibitor drug that helps to palliate erectile dysfunction. This medicine can act on the root cause of erectile dysfunction. It works to inhibit this enzyme at a cellular level. This enzyme causes a contraction of arteries, which blocks the blood flow. It helps to prevent cyclic Guanosine Monophosphate (cGMP). In short, this drug stops the production of this enzyme called phosphodiesterase-5 (PDE5) temporarily. After this reaction, the body makes nitric oxide in a higher amount, which helps in improving blood flow in the whole body, including to the penile organ. This reaction helps a man to attain an erection when a man is sexually stimulated. Megalis effect lasts up to 36 hours.