Since its approval in the United States two months ago, Viagra, or sildenafil citrate, has received more press attention than just about any other new drug in recent memory. And because it treats male impotence, this normally hushed subject has moved into the limelight. Men who have suffered in silence for years now think they have found the miracle drug. The Viagra issue is of great interest to men of all ages, but particularly those over 50 approaching the 'mid-life' or 'male menopause' phase. It is being hailed as a revolutionary drug that will do for men what birth control pills did for women in the 1960s and Prozac for the depressed in the 1980s. As with other 'miracle' drugs, this one was discovered by accident, when it was undergoing clinical trials as a treatment for patients with chest pain caused by lack of oxygen to the heart muscles. While the drug failed to control the chest pain, many patients reported unexpected genital side-effects: Viagra had a direct effect on the genital region, causing enhanced blood flow. Male sexual dysfunction is much more common than previously thought. One study found 50 per cent of men between the ages of 40 and 70 have experienced impotence at some point. As men approach their late 40s, they may experience increasing sexual dysfunction. But it is also important to remember that stress, anxiety, depression and the lack of an intimate, emotionally satisfying relationship can all contribute. There are many reasons why Viagra has become so wildly popular. It is the first and only oral medication to specifically treat impotence. At present, the common treatment includes unpleasant alternatives such as prosthetic implants, inserts, injections and vacuum pumps. These have limited success, in large part due to the reluctance of patients to use them. Viagra is also extremely effective, resulting in restoration of erectile function in more than 70 per cent of men whose underlying cause is mostly psychological. However, when the underlying cause is medical, such as in men whose circulation is impaired due to diabetic vascular changes, the response to Viagra drops to about 50 per cent. For those who suffer from impotence following surgery to correct prostate problems, the success rate is even lower. The major side-effects include headaches, facial flushing, stomach disturbances, sleep difficulties and anxiety. Many of these are directly related to the vasodilation effects of the drug. Even men left impotent by spinal cord injuries have responded to some degree. The drug seems to work quickly: within an hour of taking the tablet, men can experience erections. The drug also has significant implications for women. Many researchers believe sexual dysfunction in women is far more prevalent than in men. During sexual arousal, blood flow is known to be increased in the women's genitals. With ageing, women also experience increasingly more common sexual problems, but they are manifested in different ways from men. Women experience vaginal dryness, itching, pain with intercourse, and the inability to experience orgasms. Work is already under way in Europe to test Viagra's effects on women. However, many physicians have already declared they will not hesitate to prescribe it for female patients with the proper medical indications, due to the drug's promising effects. There are several other new drugs for sexual dysfunction - oral medications as well as in cream form - undergoing clinical trials in both men and women. Most have a similar mechanism to Viagra, working by dilating blood vessels. Viagra is at present only legally available in the US. To obtain it you have to consult a licensed American physician able to write a prescription to be filled by most pharmacies there. But some drug stores have already run out of supply due to the high demand, despite the high cost of US$10 (about HK$77.35) a dose.