Common side effects of Tadalafil include headache, flushing, indigestion, nasal congestion, back pain, and muscle aches. These side effects are usually mild to moderate and often diminish as the body adjusts to the medication. Serious but rare side effects may include sudden vision or hearing loss, and priapism (prolonged erection). Seek medical attention if you experience any severe side effects.Megalis 20 mg should not be used with nitrates (often prescribed for chest pain) or with alpha-blockers (used to treat hypertension), as this can cause a significant drop in blood pressure. It should be used cautiously in men with certain medical conditions, such as heart disease or liver and kidney impairment.