What causes erectile dysfunction?
Many medical conditions and medications can cause ED. Smoking, alcohol abuse, drug abuse, stress, and depression can also cause ED. Considering erectile function as a neurovascular event, we can divide the causes of ED into those that affect the brain and nerves (neurologic) and those that affect the arteries and veins (vascular).
Neurologic Conditions That Cause ED
A variety of neurologic conditions can cause ED. The most common of these are spinal cord injury, lumbar disk disease, stroke, Parkinson’s disease, multiple sclerosis, Alzheimer’s disease, and pituitary disease (pituitary adenoma). In addition, certain surgical procedures, such as radical prostatectomy for prostate cancer and surgery for rectal cancer, can injure the pelvic nerves. The incidence of ED after radical prostatectomy varies according to whether the patient experienced ED before surgery and whether a nerve-sparing procedure was performed. Reported rates of ED after bilateral nerve-sparing radical prostatectomy range from 18 to 82%. Other factors unrelated to disease or surgery can also cause ED. For example, long-distance bicycle riding on bicycles with small, hard seats has been implicated as a cause of ED, possibly by nerve or vascular compression.
Vascular Conditions That Cause ED
From a vascular standpoint, any disease process that can affect arteries may also affect the arteries that supply the penis. Men with coronary artery disease (sometimes manifested as angina, which is a pain in the chest, with a feeling of suffocation), cerebrovascular disease (which may have caused prior stroke or transient ischemic attack), peripheral vascular disease (decreased blood flow to the legs, often associated with aches/cramps in the legs when attempting to walk for a distance), high blood pressure, and high cholesterol levels are at increased risk for erectile troubles. Men who have experienced severe pelvic or perineal trauma, such as from a motor vehicle accident causing a pelvic fracture or direct injury to the penis, are at risk for ED.
Radiation therapy (administration of radiation to kill cancer cells) to the pelvis for colon cancer or prostate cancer can cause damage to the blood vessels supplying the penis. ED has been reported in 15 to 65% of men undergoing external-beam radiation therapy (high-energy radiation beams passed through the skin) for prostate cancer. The onset of ED after radiation therapy is usually not immediate; it typically occurs 2 or more years after the radiation therapy. Interstitial seed therapy for prostate cancer also affects erectile function in 25 to 60% of men who undergo it. As with external-beam radiation therapy, the effect on erectile function is usually seen a year or more after seed placement. Smoking causes vasospasm, or tightening up of the arteries, but it also may cause atherosclerosis, or hardening of the arteries. Venous leaks or abnormal veins may result from prior trauma and may be identified in Peyronie’s disease, a benign condition affecting the penis in middle-aged men.
Other Conditions That Cause ED
ED occurs to different degrees in different medical conditions. For example, erectile dysfunction occurs in about 27% of men with hypertension. The Massachusetts Male Aging Study found an association between low concentration of high-density lipoproteins (HDL— the good cholesterol) and ED, even though there was no correlation between ED and total cholesterol levels. (Cholesterol is a fatlike substance that is important to certain body functions but, when present in excessive amounts, contributes to unhealthy fatty deposits in the arteries, which may interfere with blood flow.) In men between the ages of 40 years and 55 years, the risk of moderate ED increased from 6.7 to 25% when the HDL level decreased from 90 to 30 mg/dL. This study also found a similar effect of the HDL level on erectile function in the older male population. Another study did find a relationship between the total cholesterol and erectile function; according to this study, the risk of ED increased as total cholesterol level increased.
This study also found a negative correlation between HDL level and risk of ED—meaning that the higher the HDL level, the lower the risk of ED. This increased risk of ED with low HDL levels and elevated cholesterol levels is not surprising, because these are the factors that increase one’s risk of cardiovascular disease.
Another condition in which ED commonly occurs is diabetes mellitus. An estimated 15.7 million people in the United States have diabetes, including 7.5 million men. Type 2 diabetes, also called noninsulin-dependent diabetes mellitus, accounts for 90-95% of the patients with diabetes mellitus; type 1 diabetes, or insulin-dependent diabetes mellitus, accounts for 5-10%. The prevalence of ED in diabetes ranges from 35 to 75%. In men with treated diabetes mellitus in the Massachusetts Male Aging Study, the age-adjusted prevalence of complete ED (no erections at any time) was 28%, which was about three times higher than the prevalence of complete ED in the entire sample of men in the Massachusetts Male Aging Study.
ED occurs in a large number (82%) of men on hemodialysis for renal (kidney) failure. Men on hemodialysis are more likely to experience ED if they are older, if they have diabetes mellitus, and if they do not use angiotensin-converting enzyme (ACE) inhibitors. The cause of the ED is probably multifactorial; it may be partly related to the medical condition that caused the renal failure (e.g., diabetes mellitus), but it also may be related to hormonal changes that occur with dialysis. Dialysis patients have lower testosterone levels and may have high prolactin levels. In addition, dialysis lowers zinc levels and may cause overactivity of the parathyroid gland (hyperparathyroidism).
Smoking may be an independent risk factor for ED, particularly erectile dysfunction caused by vascular disease, and it may also contribute to other causes of ED. In the Massachusetts Male Aging Study, neither the number of cigarettes smoked nor the duration of time smoking had an effect on the incidence of ED. However, the study did show a significant relationship between smoking and erectile dysfunction for certain categories of men. In men who were being treated for heart disease, complete ED was 56% for current smokers, compared with 21% for nonsmokers, after correction for differences in age. Similar results were noted for men with high blood pressure (20% incidence of erectile dysfunction in current smokers versus 8.5% in nonsmokers), those with arthritis (20% in current smok- ers versus 9.4% in nonsmokers), those taking heart medications (41% in current smokers versus 14% in nonsmokers), and those taking medications for high blood pressure (21% for current smokers versus 7.5% in nonsmokers).
Where alcohol use is concerned, as the saying goes, “Too much of a good thing is bad.” Alcohol is thought of as a relaxant, and its use will take away one’s inhibitions. Yet alcohol abuse—regular drinking to excess— can cause ED; occasional use does not. Liver failure as a result of alcohol abuse may also affect erectile function.
Purely psychogenic (originating from the mind or psyche) ED probably accounts for only 10% of the patients with ED. Depression, anxiety, and stress may have an adverse effect on erectile function, and many of the medications used to treat these problems can cause ED and other forms of sexual dysfunction. However, in most situations, once erectile dysfunction occurs the man develops psychogenic components related to the anxieties that ED causes. Psychogenic causes of ED include:
- Performance anxiety
- Marital problems
- Dysfunctional attitude toward sex
- Sexual phobia
- Religious beliefs/inhibitions
- Prior traumatic sexual experience
A variety of other medical conditions have been associated with ED, including endocrine abnormalities, such as hyperthyroidism (overactive thyroid gland), hypothyroidism (underactive thyroid gland), hypogonadism (when the testes don’t produce enough testosterone), and pituitary dysfunction (sometimes manifested by hyperprolactinemia, or excess prolactin production).
Medications that Cause ED
Hypertension (high blood pressure) may be a risk factor for ED, and several blood pressure medications (antihypertensives) have been described as causing ED. Most notably beta-blockers, such as metoprolol, atenolol, and labetolol, and thiazide diuretics, such as hydrochlorothiazide. The only thiazide diuretic that has not been associated with ED is indapamide.
Clonidine (Catapres), another blood pressure medication, is also associated with an increased incidence of ED.
The incidence of ED in patients taking antidepressants has been reported to be as high as 35%. Tricyclic antidepressants, such as imipramine (Tofranil), amitriptyline (Elavil), protriptyline (Concordin), and clomipramine (Anafranil), have been reported to cause ED. It appears that they affect ejaculatory function more than erectile function. Selective serotonin reuptake inhibitors (SSRIs) were initially thought to have less of an effect on erectile function; however, studies suggest that 50% of men who are taking SSRIs may experience ED. There have been reports of ED being associated with fluvoxamine (Luvox), fluoxetine (Prozac), sertraline (Zoloft), and paroxetine (Paxil). In rare cases, ED has improved with SSRI use. Antipsychotics such as thioridazine (Mellaril), fluphenazine (Prolixin), and thiothixene (Navane) have also been associated with ED, with up to 44% men taking thioridazine reporting ED. Benzodiazepines, used to treat such conditions as posttraumatic stress disorder, may also cause ED. Clonazepam (Klonopin) use has been associated with a 43% incidence of ED, whereas the other benzodiazepines and the tranquilizers diazepam (Valium), lorazepam (Ativan), and alprazolam (Xanax) have not been associated with ED.
Cimetidine (Tagamet), a histamine2-antagonist used for gastrointestinal irritation, has been reported to cause ED in 40% of men. It is known to prevent testosterone from functioning and may also increase prolactin levels, which can lower testosterone levels, decrease libido, and affect erectile function. The other histamine2-antago- nists, ranitidine (Zantac) and famotidine (Pepcid), do not have the same effect on testosterone and are not as frequently associated with ED.
Medications used to lower one’s cholesterol (lipid) level such as clofibrate (Atromid-S), gemfibrozil (Lopid), pravastatin (Pravachol) and lovastatin (Mevacor) may also affect erectile function. Digoxin, a cardiac medication, has also been associated with ED, as have the seizure medications phenytoin (Dilantin), carbamazepine (Tegretol), primidone (Mysoline), and phenobarbitol (10 to 20% incidence).
Hormone therapies for prostate cancer, such as leuprolide (Lupron) and goserelin (Zoladex), orchiectomy, and estrogen, have a negative effect on erectile function. Recreational drugs, including alcohol, cocaine, marijuana, and heroin, may also have a negative effect on erectile function. Up to 50 to 80% of alcoholics experience ED; the ED may resolve with prolonged abstinence, but in some men it may persist. Marijuana decreases testosterone levels, and long-term marijuana use may affect erectile function. Opiate addiction is commonly associated with loss of libido (interest in sex) and ED. With abstinence from opiates, the ED improves. Anabolic steroids, used by body builders and athletes to increase their muscle mass, cause testicular atrophy and decrease testosterone production, which may decrease sperm production, decrease libido, and cause ED. If the anabolic steroids are discontinued, it may take 4 months for the testicles to start producing enough testosterone to restore erectile function to normal. The medication ketoconazole, if taken in large quantities, may also affect testosterone production and affect erectile function.