Fildena 100 mg is a prescription medication used to treat erectile dysfunction. It is a generic version of Viagra, and it contains the same active ingredient, sildenafil citrate. Fildena 100 mg works by relaxing muscles in the penis, which allows for better blood flow and helps to achieve and maintain an erection. The most common side effects of Fildena 100 mg include headache, flushing, upset stomach, and back pain. Serious side effects are rare, but they can occur. If you experience any serious side effects, stop taking Fildena 100 mg and seek medical attention immediately.