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Impotence (Erectile dysfunction)HighlightsErectile Dysfunction Erectile dysfunction, also called impotence, can affect men of all ages, although it is much more common among older men. It is normal for men to occasionally experience erectile dysfunction. However, if the problem becomes chronic, it can have adverse effects on relationships, emotional health, and self-esteem. Erectile dysfunction may also be a symptom of an underlying health condition. If erectile dysfunction becomes an on-going problem, it is important to talk to your doctor. Causes of Erectile Dysfunction
Treatment Many treatments are available for erectile dysfunction. They include oral medications, injections, mechanical devices, surgery, and psychotherapy. Any health condition that may be associated with erectile dysfunction should also be addressed. Doctors recommend that a man’s partner be involved in the discussion of treatment options. PDE5 Inhibitors The most common medical treatment for erectile dysfunction is PDE5 inhibitor drugs:
These drugs are generally safe and effective for most men. These medications may not be appropriate for men with certain health conditions, such as severe heart disease, heart failure, history of stroke, or uncontrolled high blood pressure or diabetes. Men who take nitrate drugs cannot use PDE5 inhibitors, and these drugs can also interact with other medications. Talk to your doctor about whether PDE5 inhibitor drugs are a safe choice for you. IntroductionErectile dysfunction (impotence) is the inability to achieve or maintain an erection sufficiently rigid for sexual intercourse. Sexual drive and the ability to have an orgasm are not necessarily affected. Because all men have erection problems from time to time, doctors consider erectile dysfunction to be present if attempts at intercourse fail at least 25% of the time. Erectile dysfunction is not new in either medicine or human experience, but it is not easily or openly discussed. Cultural expectations of male sexuality inhibit many men from seeking help for a disorder that can usually benefit from medical treatment. The Penis and Erectile FunctionThe Structure of the Penis. The penis is composed of the following structures:
These structures are made up of erectile tissue. Erectile tissue is rich in tiny pools of blood vessels called cavernous sinuses. Each of these vessels are surrounded by smooth muscles and supported by elastic fibrous tissue composed of a protein called collagen. Erectile Function and Nitric Oxide. The penis is either flaccid or erect depending on the state of arousal. In the flaccid, or unerect, penis, the following normally occurs:
During arousal the following occurs:
Important Substances for Erectile HealthA proper balance of certain chemicals, gases, and other substances is critical for erectile health. Collagen. The protein collagen is the major component in structural tissue in the body, including in the penis. Excessive amounts, however, form scar tissue, which can impair erectile function. Oxygen. Oxygen-rich blood is one of the most important components for erectile health. Oxygen levels vary widely from reduced levels in the flaccid state to very high in the erect state. During sleep, a man can normally have three to five erections per night, bringing oxygen-rich blood to the penis. Testosterone and Other Hormones. Normal levels of hormones, especially testosterone, are essential for erectile function, though their exact role is not clear. Erectile Dysfunction and Oxygen DeprivationThe primary cause of oxygen deprivation is ischemia -- the blockage of blood vessels. The same blood flow-reducing conditions that lead to heart disease, such as atherosclerosis, may also contribute to erectile dysfunction. Conditions such as unhealthy cholesterol levels, diabetes, and high blood pressure are associated with atherosclerosis and heart disease. CausesOver the past decades, the medical perspective on the causes of erectile dysfunction has shifted. Common wisdom used to attribute almost all cases of impotence to psychological factors. Now doctors believe that up to 85% of impotence cases are caused by medical or physical problems. Only 15% are completely psychologically based. Sometimes, erectile dysfunction is due to a combination of physical and psychological causes. A number of medical conditions share a common problem with erectile dysfunction -- the impaired ability of blood vessels to open and allow normal blood flow. Heart Disease, Atherosclerosis, and High Blood PressureHeart disease, atherosclerosis, high blood pressure and high cholesterol levels are major risk factors for erectile dysfunction. In fact, erectile problems may be a warning sign of these conditions in men at risk for atherosclerosis. Men who experience ED have a greater risk for angina, heart attack, or stroke. [For more information, see In-Depth Report #3: Coronary artery disease.] Erectile dysfunction is a very common problem in men with high blood pressure. More than 40% of men with erectile dysfunction have hypertension. Many of the drugs used to treat hypertension (such as calcium channel blockers and beta-blockers) may also cause ED. [For more information, see In-Depth Report #14: High blood pressure.] DiabetesDiabetes is a major risk factor for erectile dysfunction. Between 30 - 50% of all men with diabetes report some form of sexual difficulty. Blocked arteries and nerve damage are both common complications of diabetes. When the blood vessels or nerves of the penis are involved, erectile dysfunction can result. Diabetes is also associated with heart disease and chronic kidney disease, other risk factors for ED. [For more information, see In-Depth Report #60: Diabetes type 2.] ObesityObesity increases the risk for diabetes, heart disease, and erectile dysfunction. Metabolic SyndromeMetabolic syndrome -- a cluster of conditions that includes obesity and abdominal fat, unhealthy cholesterol and triglyceride levels, high blood pressure, and insulin resistance -- is also a risk factor for erectile dysfunction in men older than 50 years. Benign Prostatic HyperplasiaSurgery and drug treatments for benign prostatic hyperplasia, such as finasteride (Proscar), can also increase the risk for impotence. [For more information, see In-Depth Report #71: Benign prostatic hyperplasia.] Neurologic ConditionsDiseases that affect the central nervous system can cause erectile dysfunction. These conditions include Parkinson's disease, multiple sclerosis, and stroke. [For more information, see In-Depth Reports #51: Parkinson's disease; #17: Multiple sclerosis; #45: Stroke.] Endocrinologic and Hormonal ConditionsLow levels of the male hormone testosterone can be a contributing factor to erectile dysfunction in men who have other risk factors. (Low testosterone as the sole cause of erectile dysfunction affects only about 5% of men. In general, low testosterone levels are more likely to reduce sexual desire than to cause impotence.) Abnormalities of the pituitary gland that cause high levels of the hormone prolactin are also associated with erectile dysfunction. Other hormonal and endocrinologic causes of erectile dysfunction include thyroid and adrenal gland problems. Physical Trauma and InjurySpinal cord injury and pelvic trauma, such as a pelvic fracture, can cause nerve damage that results in impotence. Other conditions that can injure the spine and effect impotence include spinal cord tumors, spina bifida, and a history of polio. SurgerySurgery for Prostate Cancer. Radical prostatectomy can cause loss of sexual function. Nerve-sparing surgical procedures are proving to be helpful in reducing the risk of impotence. (Radiation treatments for prostate cancer also cause erectile dysfunction.) [For more information, see In-Depth Report # 33: Prostate cancer.] Surgery for Colon and Rectal Cancers. Surgical and radiation treatments for colorectal cancers can cause impotence in some patients. In general, colostomy does not usually affect sexual function. However, wide rectal surgery can cause short-term or long-term sexual dysfunction. [For more information, see In-Depth Report #55: Colon and rectal cancers.] Fistula Surgery. Surgery to repair anal fistulas can affect the muscles that control the rectum (external anal sphincter muscles), sometimes causing impotence. (Repair of these muscles may restore erectile function.) Orthopedic Surgery. Erectile dysfunction can sometimes result from orthopedic surgery that affects pelvic nerves. Note: Vasectomy does NOT cause erectile dysfunction. MedicationsMany medications increase the risk for erectile dysfunction. They include:
Psychological CausesAnxiety. Anxiety has both emotional and physical consequences that can affect erectile function. It is among the most frequently cited contributors to psychological impotence. Stress. Even simple stress can affect sexual dysfunction. Depression. Depression can reduce sexual desire and is associated with erectile dysfunction. Relationship Problems. Troubles in relationships often have a direct impact on sexual functioning. Partners of men with erectile dysfunction may feel rejected and resentful, particularly if the affected man does not confide his own anxieties or depression. Tension and anger frequently arise between people who are unable to discuss sexual or emotional issues with each other. It can be very difficult for the man to perform sexually when both partners harbor negative feelings. Risk FactorsMore than 18 million American men over age 20 have erectile dysfunction, and about 600,000 men age 40 - 70 experience erectile dysfunction to some degree each year. AgeFor most men, erectile dysfunction is primarily associated with older age. While ED affects less than 10% of men in their 20s, and 5 - 17% of men in their 40s, about 15 - 34% of men in their 70s have ED. Nevertheless, impotence is not inevitable with age. In a survey of men over 60 years old, 61% reported being sexually active, and nearly half derived as much if not more emotional benefit from their sex lives as they did in their 40s. Severe erectile dysfunction often has more to do with disease than age itself. In particular, older men are more likely to have heart disease, diabetes, and high blood pressure than younger men. Such conditions and some of their treatments are causes of erectile dysfunction. Lifestyle FactorsSmoking. Smoking contributes to the development of impotence, mainly because it increases the effects of other blood vessel disorders, including high blood pressure and atherosclerosis. Alcohol Use. Heavy drinking can cause erectile dysfunction. Alcohol depresses the central nervous system and impairs sexual function. Drug Abuse. Illicit drugs such as heroin, cocaine, methamphetamines, and marijuana can affect sexual function. Lack of Exercise. A sedentary lifestyle can lead to obesity and other health problems associated with erectile dysfunction. DiagnosisThe doctor typically interviews the patient about many physical and psychological factors and performs a physical exam. Medical HistoryThe doctor should take a medical and personal history and may ask about the following:
In addition the doctor will ask about the patient's sexual history, which may include:
If appropriate, the doctor may also interview the sexual partner. Physical ExaminationThe doctor will perform a physical exam, including examination of the genital area and a digital rectal examination (the doctor inserts a gloved and lubricated finger into the patient's rectum) to check for prostate abnormalities. It is important to check the blood pressure and to evaluate the circulation by checking pulses in the legs. Laboratory TestsBlood tests may be used to measure testosterone levels to determine if there are hormone problems. The doctor may also screen for thyroid and adrenal gland dysfunction. In addition, the doctor may order tests for blood sugar (glucose) levels to check if diabetes is a factor. For more sophisticated tests, the doctor may refer the patient to a urologist. Because erectile dysfunction and atherosclerosis are often linked, it is important to check cholesterol levels. TreatmentMany physical and psychological situations can cause erectile dysfunction, and brief periods of impotence are normal. Every man experiences erectile dysfunction from time to time. Nevertheless, if the problem is persistent, men should seek professional help, particularly since erectile dysfunction is usually treatable and may also be a symptom of an underlying health problem. It is important to treat any medical condition that may be causing erectile dysfunction. Treatment ChoicesDrug therapy with PDE5 inhibitors is the main treatment for erectile dysfunction. Sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis) are the three PDE5 inhibitor drugs approved for treatment erectile dysfunction. In general, if a man is a candidate for PDE5 inhibitor therapy and is satisfied with the results, no further treatment is necessary. PDE5 inhibitors are not safe or effective for all men. Men who cannot or choose not to take the drugs may have other options, including:
Ultimately, how successful the medical treatment is and how well it is accepted depends, in large part, on the man's expectations and how he and his partner both adapt to the procedure. Psychotherapies. Some form of psychological, behavioral, or sexual therapy may be recommended for certain patients. Lifestyle Changes. No matter what the treatment, embarking on a healthy lifestyle is the first and critical step for restoring and maintaining erectile function. Oral Medications (PDE5 Inhibitors)Three medicines taken by mouth are approved for the treatment of erectile dysfunction:
These drugs all work equally well. All three are known as phosphodiesterase-5 (PDE5) inhibitors. By blocking the PDE-5 enzyme, these drugs help the smooth muscles of the penis to relax and increase blood flow. PDE5 inhibitors are generally the first choice of treatment for erectile dysfunction. Candidates for PDE5 InhibitorsPDE5 inhibitors are a good choice for men at any age who are in good health and who do not have conditions that preclude taking them. However, PDE5 inhibitors are not suitable for everyone. Men who take nitrate drugs for angina, or certain types of alpha-blockers for high blood pressure and benign prostatic hyperplasia, should not take PDE5 inhibitors. The PDE5 inhibitors are less effective in men with diabetes and in men who have been treated for prostate cancer. Men with the following conditions should not take PDE5 inhibitors without the recommendation of their doctors and even then should use them with caution:
Administration and EffectPDE5 inhibitors work only when the man experiences some sexual arousal. They are generally effective within 15 - 45 minutes. Sildenafil should be taken on an empty stomach; vardenafil and tadalafil may be taken with or without food. The effects of these drugs may last for several hours, and tadalafil may last for up to 36 hours. PDE5 inhibitors should not be used more than once a day. Success rates increase with the number of attempts, so a man should not be discouraged if the drug does not work at first. PDE5 inhibitors can also be used in combination with testosterone replacement therapy for men with hypogonadism (low testosterone levels). Side EffectsCommon side effects of PDE inhibitors include flushing, upset stomach, headache, nasal congestion, back pain, and dizziness. Effects on the Heart. There have been reports of fatal heart attacks in a small percentage of men taking sildenafil (Viagra). Viagra can cause sudden and dangerous drops in blood pressure when the drug is taken with nitrate drugs, such as nitroglycerine, which are used for angina. No one taking nitrates, including amyl nitrate, should take sildenafil or any other PDE5 inhibitors. Intercourse itself involves an increase in physical exertion and a small risk of heart attack for patients with known heart disease or those at risk. Visual Effects. About 2.5% of men who take these drugs develop vision problems that include seeing a blue haze, temporary increased brightness, and even temporary vision loss in a few cases. The effect is usually temporary, lasting a few minutes to several hours. Men at risk for eye problems who take PDE5 inhibitors regularly should have frequent eye examinations with an ophthalmologist. Men should also see an eye doctor if visual problems last more than a few hours. In a few cases, these drugs have been associated with partial vision loss. The vision loss was caused by non-arteritic anterior ischemic optic neuropathy (NAION), a condition that occurs from poor blood flow to optic nerves. However, doctors note that erectile dysfunction is itself linked to the same vascular problems that cause NAION. Patients who suffer from diabetes, high blood pressure, and heart disease are at higher risk for erectile dysfunction as well as other vascular problems such as NAION. Information concerning vision loss has been added to the labels of these drugs, but the risk of blindness appears small. Still, patients who use this medication and experience a sudden loss of vision should immediately stop taking the drug and contact their doctor. Hearing Loss. A small number of men have experienced sudden hearing loss in one ear, sometimes accompanied by ringing in the ears and dizziness. If you have this symptom, immediately contact your doctor. Seizures. There have been a few reports of seizures in men taking sildenafil. These are rare occurrences and it is not clear if there is any causal association. Risk of Priapism. PDE5 inhibitors pose a very low risk for priapism in most men. (Priapism is sustained, painful, and unwanted erection.) Exceptions are young men with normal erectile function. Interactions with Other Drugs. In addition to serious interactions with nitrates, PDE5 inhibitors may also interact with certain antibiotics, (such as erythromycin), and acid blockers, such as cimetidine (Tagamet). Patients should tell their doctor about any other medications they are taking. Injections or Topical TreatmentsTreatments Using AlprostadilAlprostadil is derived from a natural substance, prostaglandin E1, which opens blood vessels. This medicine is an effective treatment for some men. It can be administered by:
Candidates. Alprostadil is not an appropriate choice for men with:
Injected Alprostadil. Injected alprostadil (Caverject, Edex) uses a very small needle that the man injects into the erectile tissue of his penis. About 80% of men describe the pain of administering the injection as very mild. The drug should not be injected more than 3 times a week or more than once within a 24-hour period. MUSE System. The MUSE system delivers alprostadil through the urethra. It works in the following way:
The MUSE system should not be used more than twice a day and is not appropriate for men with abnormal penis anatomy. Side Effects of Most Alprostadil Methods. Certain side effects are common to all methods of administration, although they may differ in severity depending on how the drug is given:
Injections Using Papaverine and PhentolamineUntil the introduction of alprostadil, the two drugs used for injection therapy had been papaverine (Pavabid, Cerespan) and phentolamine (Regitine). Adverse reactions are usually minor but include pain, ulcers, and prolonged erections (priapism). These drugs are rarely used now. Testosterone Replacement TherapyTestosterone replacement therapy works best for men with ED who have been diagnosed with hypogonadism (low testosterone levels). Men who have ED and normal testosterone levels are not likely to benefit from testosterone therapy. Studies indicate that testosterone therapy can modestly improve erectile function and libido. Forms of testosterone therapy include:
Side effects may include acne, breast enlargement, headache, and emotional instability. Testosterone therapy may increase the risk for the following serious side effects:
Surgery and DevicesVacuum Erection DevicesVacuum erection devices, also called vacuum constriction devices, can generally be used by all men with erectile dysfunction. Patients must receive thorough instructions in the proper use of such devices. They typically work as follows:
Lack of spontaneity is this method's major drawback. Penile ImplantsPenile implants are an option for men who cannot take medication or for who less invasive treatments do not work. In general, they work well in restoring sexual function, and men are usually satisfied with the results. Two types of surgical implants are used for the treatment of erectile dysfunction:
Erectile tissue is permanently damaged when these devices are implanted, and these procedures are irreversible. Although uncommon, mechanical breakdown can occur, or the device can slip or bulge. In addition, a less than optimal quality of erection may result. Infection is a rare, but serious, complication. Vascular SurgeryIn rare cases, penile vascular surgery may be considered as treatment for erectile dysfunction. Two types of operations are available: revascularization (bypass) surgery, and venous ligation. Some insurance carriers consider these procedures experimental and will not pay for them. According to the American Urologic Association, men who smoke or who have the following conditions are not candidates for penile vascular surgeries:
Revascularization. The revascularization procedure usually involves taking an artery from a leg and then surgically connecting it to the arteries at the back of the penis, bypassing the blockages and restoring blood flow. Penile arterial revascularization is appropriate only for young men (under age 45) who have blood vessel injury at the base of the pain that was caused by events such as blunt trauma or pelvic fracture. Venous Ligation. Venous ligation is performed when the penis is unable to store a sufficient amount of blood to maintain an erection. This operation ties off or removes veins that are causing an excessive amount of blood to drain from the erection chambers. Long-term success rates for this procedure are less than 50 percent. Lifestyle ChangesBecause many cases of erectile dysfunction are due to reduced blood flow from blocked arteries, it is important to maintain the same lifestyle habits as those who face an increased risk for heart disease. Diet and ExerciseDiet. Everyone should eat a diet rich in fresh fruits and vegetables, whole grains, and fiber and low in saturated fats and sodium. Because erectile dysfunction may be related to circulation problems, diets that benefit the heart are especially important. Foods that some people claim to have qualities that enhance sexual drive include chilies, chocolate, scallops, oysters, olives, and anchovies. No evidence exists for these claims. Exercise. A regular exercise program can be helpful. Alcohol and Smoking. Men who drink alcohol should do so in moderation. Quitting smoking is essential. Stay Sexually ActiveStaying sexually active may help prevent impotence. Frequent erections stimulate blood flow to the penis. Change or Reduce MedicationsIf medications are causing impotence, the patient and doctor should discuss alternatives or reduced dosages. Psychotherapy and Behavioral TherapyEven if erectile dysfunction is caused by a physical problem, interpersonal, supportive, or behavioral therapy are often helpful for patients and their partners. Herbs and SupplementsGenerally, manufacturers of herbal remedies and dietary supplements do not need FDA approval to sell their products. Just like a drug, herbs and supplements can affect the body's chemistry, and therefore have the potential to produce side effects that may be harmful. There have been a number of reported cases of serious and even lethal side effects from herbal products. Patients should always check with their doctors before using any herbal remedies or dietary supplements. Aphrodisiacs are substances that are supposed to increase sexual drive, performance, or desire. Many herbs and dietary supplements are marketed as aphrodisiacs. There are several special concerns for people taking alternative remedies for erectile dysfunction. Yohimbe. Yohimbe is derived from the bark of a West African tree. Side effects include nausea, insomnia, nervousness, and dizziness. Large doses of yohimbe can increase blood pressure and heart rate and may cause kidney failure. Viramax is a commercial product that contains yohimbine, the active chemical ingredient of yohimbe, and three other herbs: catuaba, muira puama, and maca. It has not been proven to be either effective or safe, and interactions with medications are unknown Gamma-Butyrolactone (GBL). GBL is found in products marketed for improving sexual function (Verve, Jolt). This substance can convert to a chemical that can cause toxic and life-threatening effects, including seizures and even coma. Gingko Biloba. Although the risks for gingko biloba appear to be low, there is an increased risk for bleeding at high doses and interaction with vitamin E, anti-clotting medications, and aspirin and other NSAIDs. Large doses can cause convulsions. Commercial gingko preparations have also been reported to contain colchicine, a substance that can be harmful in people with kidney or liver problems. L-arginine (also called arginine). Arginine may cause gastrointestinal problems. It can also lower blood pressure and change levels of certain chemicals and electrolytes in the body. It may increase the risk for bleeding. Some people have an allergic reaction to it, which in some cases may be severe. It may worsen asthma. Dehydroepiandrosterone (DHEA). DHEA is a supplement related to certain male and female hormones. Studies show inconclusive results in its treatment for erectile dysfunction. DHEA may interact dangerously with other medications. Spanish Fly. Spanish fly, or cantharides, which is made from dried beetles, is the most widely-touted aphrodisiac but can be particularly harmful. It irritates the urinary and genital tract and can cause infection, scarring, and burning of the mouth and throat. In some cases, it can be life threatening. No one should try any aphrodisiac without consulting a doctor. Other Dietary Supplements Marketed for Erectile Dysfunction. There are numerous other products marketed as "all-natural" dietary supplements and promoted as treatments for erectile dysfunction and sexual enhancement. The FDA has not approved any of these products. In recent years, the FDA has banned from the market many of these dietary supplements and warns that they contain the same or similar PDE5 inhibitor prescription drugs used in Viagra, Cialis, and Levitra. Resources
ReferencesBabaei AR, Safarinejad MR, Kolahi AA. Penile revascularization for erectile dysfunction: a systematic review and meta-analysis of effectiveness and complications. Urol J. 2009 Winter;6(1):1-7 Bhasin S, Cunningham GR, Hayes FJ, Matsumoto AM, Snyder PJ, Swerdloff RS, et al. Testosterone therapy in adult men with androgen deficiency syndromes: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2006 Jun;91(6):1995-2010. Epub 2006 May 23. Boloña ER, Uraga MV, Haddad RM, Tracz MJ, Sideras K, Kennedy CC, et al. Testosterone use in men with sexual dysfunction: a systematic review and meta-analysis of randomized placebo-controlled trials. Mayo Clin Proc. 2007 Jan;82(1):20-8. Lindau ST, Schumm LP, Laumann EO, Levinson W, O'Muircheartaigh CA, Waite LJ. A study of sexuality and health among older adults in the United States. N Engl J Med. 2007 Aug 23;357(8):762-74. McVary, K. T.. Clinical practice. Erectile dysfunction. N Engl J Med. 2007 Dec; 357(24): 2472-81. Melnik T, Soares BG, Nasselo AG. Psychosocial interventions for erectile dysfunction. Cochrane Database Syst Rev. 2007 Jul 18;(3):CD004825. Miles CL, Candy B, Jones L, Williams R, Tookman A, King M. Interventions for sexual dysfunction following treatments for cancer. Cochrane Database Syst Rev. 2007 Oct 17;(4):CD005540. Müller A, Mulhall JP. Cardiovascular disease, metabolic syndrome and erectile dysfunction. Curr Opin Urol. 2006 Nov;16(6):435-43. Nehra A. Erectile dysfunction and cardiovascular disease: efficacy and safety of phosphodiesterase type 5 inhibitors in men with both conditions. Mayo Clin Proc. 2009 Feb;84(2):139-48. Saad F, Grahl AS, Aversa A, Yassin AA, Kadioglu A, Moncada I, et al. Effects of testosterone on erectile function: implications for the therapy of erectile dysfunction. BJU Int. 2007 May;99(5):988-92. Epub 2007 Feb 19. Selvin E, Burnett AL, Platz EA. Prevalence and risk factors for erectile dysfunction in the US. Am J Med. 2007 Feb;120(2):151-7. Vardi M, Nini A. Phosphodiesterase inhibitors for erectile dysfunction in patients with diabetes mellitus. Cochrane Database Syst Rev. 2007 Jan 24(1):CD002187.
Review Date:
7/8/2009 Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997-
A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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