Udenafil is an oral medication used to treat erectile dysfunction (ED) in men by improving blood flow to the penis. It belongs to the class of phosphodiesterase type 5 (PDE5) inhibitors, similar to sildenafil or tadalafil. Zydena works by enhancing the effects of nitric oxide, helping men achieve and maintain an erection during sexual stimulation. Its effects begin within 30–60 minutes and can last up to 24 hours.