Megalis 20 Tablet contains Tadalafil (20mg), a phosphodiesterase type 5 (PDE5) inhibitor used to treat erectile dysfunction (ED) and sometimes benign prostatic hyperplasia (BPH) in men. Tadalafil works by increasing blood flow to the penis during sexual stimulation, aiding in achieving and maintaining an erection. Common side effects include headache, flushing, back pain, and indigestion. Typically, the tablet is taken at least 30 minutes before sexual activity, and its effects can last up to 36 hours, providing a longer window of effectiveness. It is crucial to adhere to the prescribed dosage and avoid using it with nitrates or certain other medications. Consult a healthcare provider for any severe or persistent side effects or if the erection lasts longer than 4 hours (priapism).