Sildenafil is a prescription medicine commonly used to treat erectile dysfunction (ED), a condition in which a man has difficulty achieving or maintaining an erection sufficient for sexual activity. It belongs to a group of medicines called phosphodiesterase type 5 (PDE5) inhibitors. While sildenafil is available in several strengths, including 25 mg, 50 mg, and 100 mg, 150 mg is higher than the usual maximum recommended dose and should only be considered under direct medical supervision.