The Megalis pill is actively composed of tadalafil, which belongs to the category of medicines called PDE5 inhibitors. This drug can act on the root cause of erectile dysfunction by working on the cellular level. This enzyme causes a contraction in the blood vessels. It also degrades a vasodilator called cyclic Guanosine Monophosphate (cGMP). In short, the drug stops the secretion of this enzyme called phosphodiesterase-5 (PDE5) temporarily. After this reaction, the body makes nitric oxide in a higher amount, which is also a vasodilator that effectively acts to augment blood flow in the body, including to the penile organ. This process finally leads to an erection when a man is sexually stimulated. Megalis effect lasts up to 36 hours; therefore, in this span, a man can attain an erection when he is sexually aroused.