Erectile dysfunction (ED) has dozens of potential causes, and most men who experience it are dealing with more than one at the same time. The condition affects roughly 13% of men in their late twenties and early thirties, climbing to about 25% in their late forties and nearly 50% by age 65 to 74. While age is the strongest predictor, ED is not an inevitable part of aging. It results from specific, identifiable problems with blood flow, nerve signaling, hormones, or mental health, often layered on top of each other.
Blood Vessel Problems
The most common physical cause of ED is restricted blood flow to the penis. An erection depends on arteries dilating and flooding the erectile tissue with blood. Anything that narrows those arteries or stiffens their walls undermines that process. The penile arteries are only 1 to 2 millimeters wide, making them among the smallest in the body. That means plaque buildup from atherosclerosis shows up here before it causes noticeable problems in larger vessels like the coronary or carotid arteries. For many men, ED is the first visible sign of cardiovascular disease, appearing years before a heart attack or stroke.
High blood pressure compounds the problem. It ramps up the nervous system’s constricting signals to blood vessels while simultaneously remodeling the erectile tissue itself, reducing its ability to expand. In animal studies, damage to the penile blood vessels from hypertension appeared even before changes were detectable elsewhere in the body. High cholesterol works through a similar pathway: excess fats in the blood trigger inflammation that suppresses the chemical signal (nitric oxide) responsible for relaxing the smooth muscle inside the penis and allowing blood to flow in.
Diabetes and Chronic High Blood Sugar
Diabetes is one of the strongest risk factors for ED, and it attacks erectile function from multiple directions at once. Chronically elevated blood sugar generates harmful compounds that accumulate in blood vessel walls, increase oxidative stress, and reduce the availability of nitric oxide. The result is endothelial dysfunction, where the inner lining of blood vessels loses its ability to signal the surrounding muscle to relax.
At the same time, high blood sugar damages the nerves that control erections. The autonomic nerves responsible for triggering arterial dilation and smooth muscle relaxation undergo a gradual breakdown of their protective coating and internal structure. This means even if the blood vessels were healthy, the signal to start an erection may never arrive properly. Men with diabetes also frequently develop hormonal imbalances that further reduce erectile function, making it a condition where vascular, neurological, and hormonal causes converge.
Low Testosterone
Testosterone plays a direct role in erectile function by maintaining the production of nitric oxide in penile tissue. When levels drop, the enzyme responsible for generating that signal becomes less active, and the erectile tissue itself can lose smooth muscle and accumulate more fibrous tissue over time. The American Urological Association defines low testosterone as a total level below 300 ng/dL, measured on at least two separate mornings (testosterone peaks in the early hours and drops throughout the day).
Low testosterone alone doesn’t always cause ED, but it makes erections harder to initiate and sustain, and it often reduces desire, which compounds the problem. Causes of low testosterone range from aging and obesity to pituitary gland disorders, certain medications, and chronic illness. Other hormonal conditions, including thyroid disorders and elevated prolactin, can also contribute.
Neurological Conditions
Erections require a chain of nerve signals that starts in the brain, travels down the spinal cord, and reaches the penis through pelvic autonomic nerves. A disruption at any point along that chain can cause ED. Multiple sclerosis, Parkinson’s disease, stroke, and traumatic brain injury can all interfere with how the brain processes arousal or transmits the signals that trigger blood flow. Spinal cord injuries are particularly impactful because they can sever the connection between the brain and the pelvic nerves entirely.
Peripheral nerve damage matters too. Diabetic neuropathy is the most common example, but nerve compression injuries, pelvic surgery (especially prostate removal), and radiation therapy to the pelvic area can all damage the local nerves that control the mechanics of erection. The effects can be partial or complete depending on the extent of nerve involvement.
Medications
A long list of commonly prescribed drugs can cause or worsen ED. Among blood pressure medications, thiazide diuretics are the most frequent culprits, followed by beta-blockers like metoprolol and propranolol. Alpha-blockers tend to be less likely to cause the problem.
Antidepressants are another major category. SSRIs like sertraline and fluoxetine are well known for sexual side effects, but older classes of antidepressants, anti-anxiety medications like diazepam and lorazepam, and antipsychotics can all contribute. Opioid painkillers, including codeine, oxycodone, morphine, and methadone, suppress testosterone production and frequently cause ED with long-term use. Hormonal cancer treatments, particularly those used for prostate cancer, work by deliberately lowering testosterone and almost universally affect erectile function. Even some antihistamines, including diphenhydramine (Benadryl) and ranitidine, are on the list.
If you suspect a medication is contributing, the solution is never to stop taking it on your own. Switching to a different drug within the same class often resolves the issue.
Obesity and Metabolic Syndrome
Excess body fat, particularly visceral fat around the abdomen, is an independent risk factor for ED. Enlarged fat cells release inflammatory molecules, including TNF-alpha and interleukin-6, that directly suppress nitric oxide production in blood vessel walls. At the same time, excess fat tissue converts testosterone to estrogen, lowering available testosterone levels. Obesity also promotes insulin resistance, which further damages endothelial function through many of the same pathways seen in diabetes.
The relationship is dose-dependent: the more excess weight, the greater the risk. But it’s also partially reversible. Weight loss through diet and exercise has been shown to improve erectile function, even without medication, by reducing inflammation, improving blood vessel health, and raising testosterone levels.
Psychological and Emotional Causes
ED doesn’t always start with a physical problem. Anxiety, depression, stress, and relationship conflict can all trigger or maintain it. The mechanism is straightforward: the sympathetic nervous system, your body’s fight-or-flight response, is the enemy of erections. Erections depend on parasympathetic activation (the rest-and-relax branch). When anxiety spikes, the sympathetic system floods the body with stress hormones that constrict blood vessels and actively inhibit the smooth muscle relaxation needed for blood to fill the penis.
Performance anxiety creates a particularly vicious cycle. A man experiences one episode of difficulty, then monitors himself anxiously during the next encounter, which triggers more sympathetic activation, which makes the problem worse. Depression contributes through a different pathway: it disrupts the hormonal axis that regulates stress hormones and serotonin, both of which affect the physical mechanics of erection as well as desire. Complicating matters, many antidepressants prescribed for depression themselves cause ED, making it difficult to untangle the cause.
In younger men without obvious physical risk factors, psychological causes are especially common. But in practice, most cases of ED in men over 40 involve a mix of physical and psychological factors feeding each other.
Lifestyle Factors
Smoking damages the endothelial lining of blood vessels throughout the body, and the small penile arteries are among the first affected. Heavy alcohol use suppresses testosterone, damages nerves, and impairs liver function in ways that disrupt hormone metabolism. Even moderate alcohol intake can temporarily reduce erectile quality by depressing nervous system activity.
Sedentary behavior contributes independently of weight. Regular physical activity improves endothelial function, raises testosterone, reduces inflammation, and lowers stress hormones. Sleep deprivation, particularly from obstructive sleep apnea, lowers testosterone (most of which is produced during sleep) and increases sympathetic nervous system activity. Recreational drugs, including cocaine, amphetamines, and cannabis with chronic use, also carry ED risk through various vascular and hormonal pathways.
How Severity Is Measured
If you see a doctor about ED, you’ll likely be asked to fill out a short questionnaire called the IIEF-5, which scores erectile function on a scale from 5 to 25. A score of 22 to 25 is considered normal. Scores of 17 to 21 indicate mild ED, 12 to 16 mild-to-moderate, 8 to 11 moderate, and 5 to 7 severe. This helps guide treatment decisions and track whether interventions are working over time. Blood tests for testosterone, blood sugar, and cholesterol are standard parts of the workup, since many of the most treatable causes show up in routine lab results.