Megalis 20 mg is a medication that contains the active ingredient Tadalafil. Tadalafil is used to treat erectile dysfunction (ED) in men. It is a phosphodiesterase type 5 (PDE5) inhibitor, similar to medications like Viagra (Sildenafil) and Levitra (Vardenafil). Tadalafil works by increasing blood flow to the penis, which helps men achieve and maintain an erection when sexually aroused. It does not have any contraceptive or pregnancy prevention properties.