Sildenafil 100 mg is indicated for the treatment of erectile dysfunction (ED). It is also used in a different dosage and brand name to treat pulmonary arterial hypertension (PAH). The 100 mg strength of sildenafil (often associated with the brand name Viagra, though generic versions are available) is used to manage erectile dysfunction in men. Erectile Dysfunction (ED): This condition involves the inability to get or keep an erection firm enough for sexual intercourse. Sildenafil works by relaxing the blood vessels in the penis, which increases blood flow when a man is sexually excited, helping to achieve and maintain an erection. It requires sexual arousal to be effective; it does not automatically cause an erection on its own.