Under normal circumstances, when a man is sexually stimulated, his brain sends a message down the spinal cord and into the nerves of the penis. The nerve endings in the penis release chemical messengers, called neurotransmitters, that signal the arteries that supply blood to the corpora cavernosa (the two spongy rods of tissue that span the length of the penis) to relax and fill with blood. As they expand, the corpora cavernosa close off other veins that would normally drain blood from the penis. As the penis becomes engorged with blood, it enlarges and stiffens, causing an erection. Problems with blood vessels, nerves, or tissues of the penis can interfere with an erection.
Causes & symptoms
It is estimated that as many as 20 million American men frequently suffer from impotence and that it strikes up to half of all men between the ages of 40 and 70. Doctors used to think that most cases of impotence were psychological in origin, but they now recognize that, at least in older men, physical causes may play a primary role in 60% or more of all cases. In men over the age of 60, the leading cause is atherosclerosis, or narrowing of the arteries, which can restrict the flow of blood to the penis. Injury or disease of the connective tissue, such as Peyronie's disease, may prevent the corpora cavernosa from completely expanding. Damage to the nerves of the penis from certain types of surgery or neurological conditions, such as Parkinson's disease or multiple sclerosis, may also cause impotence. Men with diabetes are especially at risk for impotence because of their high risk of both atherosclerosis and a nerve disease called diabetic neuropathy.
Some drugs, including certain types of blood pressure medications, antihistamines, tranquilizers (especially when taken before intercourse), and antidepressants known as selective serotonin reuptake inhibitors (SSRIs, including Prozac and Paxil) can interfere with erections. Smoking, excessive alcohol consumption, and illicit drug use may also contribute. In some cases, low levels of the male hormone testosterone may contribute to erectile failure. Finally, such psychological factors as stress, guilt, or anxiety, may also play a role, even when the impotence is primarily due to organic causes.
When diagnosing the underlying cause of impotence, the doctor begins by asking the man a number of questions about when the problem began, whether it only happens with specific sex partners, and whether he ever wakes up with an erection. (Men whose dysfunction occurs only with certain partners or who wake up with erections are more likely to have a psychological cause for their impotence.) Sometimes, the man's sex partner is also interviewed. In some cases, domestic discord may be a factor.
The doctor also obtains a thorough medical history to find out about past pelvic surgery, diabetes, cardiovascular disease, kidney disease, and any medications the man may be taking. The physical examination should include a genital examination, hormone tests, and a glucose test for diabetes. Sometimes a measurement of blood flow through the penis may be taken.
Alternative health practitioners often forgo such extensive testing and rely on information obtained from the patient. Usually the fact that the man cannot get or maintain an erection is reason enough to begin alternative or holistic therapy.
A number of herbs have been promoted for treating impotence. The most widely touted is yohimbe (Corynanthe yohimbe), derived from the bark of the yohimbe tree native to West Africa. It has been used in Europe for about 75 years to treat erectile dysfunction. The FDA approved yohimbe as a treatment for impotence in the late 1980s. It is sold as an over-the-counter dietary supplement and as a prescription drug under brand names such as Yocon, Aphrodyne, Erex, Yohimex, Testomar, Yohimbe, and Yovital.
There is no clear medical research that indicates exactly how or why yohimbe works in treating impotence. It is generally believed that yohimbe dilates blood vessels and stimulates blood flow to the penis, causing an erection. It also prevents blood from flowing out of the penis during an erection. It may also act on the central nervous system, specifically the lower spinal cord area where sexual signals are transmitted. Studies show it is effective in 30–40% of men with impotence. It is primarily effective in men with impotence caused by vascular, psychogenic (originating in the mind), or diabetic problems. It usually does not work in men whose impotence is caused by organic nerve damage. In healthy men without impotence, yohimbe in some cases appears to increase sexual stamina and prolong erections.
The usual dosage of yohimbine (yohimbe extract) to treat erectile dysfunction is 5.4 mg three times a day. It may take three to six weeks for it to take effect. Most commercially available supplements don't contain enough yohimbe to be effective. Doctors recommend obtaining a prescription for yohimbe to get enough active ingredient for success.
Ginkgo (Ginkgo biloba) is also used to treat impotence, although it has not been shown to help the condition in controlled studies and probably has more of a psychological effect. In addition, ginkgo carries some risk of abnormal blood clotting and should be avoided by men taking such blood thinners, as coumadin. Other herbs promoted for treating impotence include true unicorn root (Aletrius farinosa), saw palmetto (Serenoa repens), ginseng (Panax ginseng), and Siberian ginseng (Eleuthrococcus senticosus). Nux vomica (Strychnos nux-vomica) has been recommended, especially when impotence is caused by excessive alcohol, cigarettes, or dietary indiscretions. Nux vomica can be very toxic if taken improperly, so it should be used only under the strict supervision of a physician trained in its use.
There are quite a few Chinese herbal remedies for impotence, usually combinations of herbs and sometimes such animal parts as deer antler and sea horse.
Years ago, the standard treatment for impotence was a penile implant or long-term psychotherapy. Although physical causes are now more readily diagnosed and treated, individual or marital counseling is still an effective treatment for impotence when emotional factors play a role. Fortunately, other approaches are now available to treat the physical causes of impotence.
The most common treatment today is with the prescription drug sildenafil citrate, sold under the brand name Viagra. An estimated 20 million prescriptions for the pill have been filled since it was approved by the FDA in March 1998. It is also the most effective treatment, with a success rate of more than 60%. The drug boosts levels of a substance called cyclic GMP, which is
The primary drawback to Viagra, which works about an hour after it is taken, is that the FDA cautions men with heart disease or low blood pressure to be thoroughly examined by a physician before obtaining a prescription. At least 130 men have died while taking Viagra. Shortly after use of the drug skyrocketed, concerns were expressed over cardiovascular effects from Viagra. However, studies reported in 2002 that sildenafil had no effect on cardiac symptoms in older men who used it. Instead, cardiac events reported with use of Viagra are more likely the result of the physical demands of sexual activity in patients using the drug who were already at higher risk for cardiovascular disease.
In the summer of 2002, two investigational drugs were announced to become available in the near future to also treat erectile dysfunction. Vardenafil and tadalafil both helped men who also had such conditions as diabetes, high blood pressure and benign prostatic hypertrophy. The drugs are awaiting final FDA approval.
Vardenafil and tadalafil belong to the same group of chemical compounds as sildenafil, namely phosphodiesterase type 5 (PDE-5) inhibitors. Some men cannot benefit from sildenafil or the two newer PDE-5 inhibitors because they have low levels of nitric oxide. British investigators reported in late 2002 that three different types of compounds are being studied as possible medications for men with low levels of nitric oxide. They are Rho-kinase inhibitors, soluble guanylate cyclase activators, and nitric oxide-releasing PDE-5 inhibitors.
Other medications under investigation as treatments for impotence are topical agents. Topical means that they are applied externally to the skin rather than being injected or taken by mouth. If approved, these drugs would provide a noninvasive alternative for men who cannot take sildenafil or other oral medications for impotence.
Other traditional therapies for impotence include vacuum pump therapy, injection therapy involving injecting a substance into the penis to enhance blood flow, and a penile implantation device. In rare cases, if narrowed or diseased veins are responsible for impotence, surgeons may reroute the blood flow into the corpus cavernosa or remove leaking vessels.
A newer approach to the treatment of erectile dysfunction is gene therapy. As of late 2002, several preclinical studies have shown promise, but none of the gene-based strategies so far have yet been tested for safety.
With proper diagnosis, impotence can nearly always be treated or coped with successfully. Unfortunately, fewer than 10% of impotent men seek treatment.
There is no specific treatment to prevent impotence. Perhaps the most important measure is to maintain general good health and avoid atherosclerosis by exercising regularly, controlling weight, controlling hypertension and high cholesterol levels, and not smoking. Avoiding excessive alcohol intake may also help.
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Ken R. Wells
Rebecca J. Frey, PhD