Forzest 20 mg contains tadalafil, a phosphodiesterase type 5 (PDE5) inhibitor used to treat erectile dysfunction (ED) in adult men. It works by increasing blood flow to the penis during sexual stimulation, helping achieve and maintain an erection. Tadalafil does not increase sexual desire and does not normally cause an erection without sexual stimulation. For ED, 20 mg is generally used as an as-needed dose, while lower doses may be appropriate for some men.