Forzest 20 mg is a medicine containing tadalafil, an active ingredient used to treat erectile dysfunction (ED) in adult men. Erectile dysfunction is a condition in which a man has difficulty achieving or maintaining an erection sufficient for sexual activity. Never combine tadalafil with nitrate medicines, such as nitroglycerin, because this can cause a dangerous drop in blood pressure. Consult a healthcare professional if you have heart disease, low blood pressure, or liver or kidney problems.