Lack of sexual desire or arousal can have medical or psychological roots. Stress, fatigue, anxiety, prior traumatic sexual trauma, or relationship problems can contribute to sexual dysfunction. Painful intercourse can be caused by physical or psychological factors. Pelvic surgery, infections, or loss of vaginal lubrication can irritate the tissues and lead to pain during intercourse. In a condition called vaginismus, the woman experiences involuntary spasm or tightening of the muscles at the entrance of the vagina.
Some women also suffer from inability to have an orgasm.
The clitoris, structurally similar to a man's penis, is dependent upon blood flow to maintain and achieve an orgasm. Any condition that affects blood flow to the area, such as high blood pressure or trauma, may contribute to problems with orgasm. The drug enhances smooth muscle relaxation in an area of the penis called the corpus cavernosum. In turn, this allows the penis to fill with blood, producing an erection. Concerns have been raised about possible side effects of the medication, such as fainting, nausea, and interaction with alcohol.