Erectile dysfunction (ED) results from a disruption in blood flow, nerve signaling, hormones, or some combination of all three. It affects roughly 39% of men by age 40 and 67% by age 70, making it one of the most common sexual health concerns men face. While occasional difficulty getting or keeping an erection is normal, persistent ED almost always has an identifiable physical or psychological cause.
How Erections Work
Understanding what goes wrong starts with understanding what’s supposed to happen. When you’re sexually aroused, your brain sends signals down through the spinal cord to nerves in the pelvis. Those nerves release a chemical called nitric oxide into the smooth muscle tissue of the penis. Nitric oxide triggers a chain reaction that relaxes the muscle walls of the penile arteries, allowing blood to rush in and fill two sponge-like chambers called the corpora cavernosa. As they expand, they press against the veins that normally drain blood out, trapping it inside. That’s what produces and maintains an erection.
Anything that interferes with the nerve signals, the nitric oxide release, the blood flow in, or the blood trapping mechanism can cause ED. Most cases involve more than one factor working together.
Blood Vessel Damage
Vascular problems are the single most common physical cause of ED. The process often starts with damage to the endothelium, the thin inner lining of your blood vessels. A healthy endothelium produces nitric oxide and keeps blood flowing smoothly. When it’s damaged, blood flow decreases throughout the body, and fatty plaques can start building up inside artery walls.
Here’s what makes ED a particularly important warning sign: the arteries supplying the penis are significantly smaller than the ones supplying the heart. That means plaque buildup restricts penile blood flow years before it causes chest pain or other heart symptoms. Research published in Circulation found that men with ED were roughly twice as likely to experience a cardiovascular event like a heart attack or stroke compared to men without ED, even after adjusting for other risk factors. In that study, 6.3% of men with ED experienced a cardiovascular event over about four years, compared to 2.6% of men without it.
This is why doctors increasingly view ED not just as a sexual health issue, but as a potential early indicator of cardiovascular disease. If you develop ED, especially before age 50, it’s worth having your heart health evaluated.
Diabetes and Metabolic Conditions
Diabetes damages blood vessels and nerves simultaneously, which is why it’s one of the strongest risk factors for ED. Chronically elevated blood sugar injures the endothelium and reduces the body’s ability to produce nitric oxide. Over time, it also damages the small nerve fibers responsible for triggering erections. Men with diabetes develop ED at higher rates and at younger ages than men without it.
High blood pressure and high cholesterol contribute through similar mechanisms. Both accelerate the hardening and narrowing of arteries, reducing the blood flow needed for a firm erection.
Low Testosterone and Hormonal Causes
Testosterone plays a supporting role in erections by maintaining sex drive and helping the body produce nitric oxide. The American Urological Association defines low testosterone as a total level below 300 ng/dL, confirmed by two separate morning blood tests. Pooled data from 29 studies shows that men with ED have testosterone levels averaging about 47 ng/dL lower than men without ED.
Low testosterone alone doesn’t always cause ED directly, but it reduces desire and can make it harder for other parts of the process to work properly. Several conditions can drive testosterone down. The pituitary gland in the brain may not be sending the right hormonal signals to the testes, or the testes themselves may be underperforming. Rarely, elevated levels of prolactin (a hormone normally associated with milk production) can suppress testosterone. Obesity is another major driver, as excess body fat converts testosterone into estrogen, shifting the hormonal balance.
Nerve and Neurological Problems
Because erections depend on precise signaling between the brain, spinal cord, and pelvic nerves, neurological conditions frequently cause ED. Multiple sclerosis affects 50% to 90% of men sexually, regardless of age, because it creates lesions in the central nervous system that disrupt those signals. The location of the lesions matters more than how long someone has had the disease.
Parkinson’s disease causes ED in an estimated 42% to 79% of affected men, partly from the loss of dopamine (a brain chemical involved in arousal and pleasure) and partly from the nerve degeneration itself. Spinal cord injuries can disrupt the pathways at their source. The body actually has two separate erection pathways through the spinal cord: one that responds to physical touch (reflexogenic) and one that responds to mental arousal (psychogenic). Depending on where a spinal injury occurs, one or both pathways may be affected.
Surgery and Pelvic Injury
Prostate surgery is one of the best-known causes of ED because the nerves controlling erections run along the outer surface of the prostate gland. Even with nerve-sparing surgical techniques, several types of damage can occur during the procedure: mechanical stretching of nerves during retraction of the prostate, heat damage from surgical tools used to control bleeding, and inflammation from the trauma of surgery itself. Recovery of erectile function after prostate surgery can take months to years, and some men never fully recover.
Bladder surgery, rectal surgery, and radiation therapy to the pelvic area carry similar risks, since they all involve the same nerve neighborhood. Pelvic fractures from accidents can also damage the blood vessels or nerves supplying the penis.
Medications That Cause ED
A surprisingly long list of common medications can contribute to ED. If your erection problems started around the time you began a new prescription, the medication may be involved.
- Blood pressure medications: Thiazide diuretics (water pills) are the most common culprits, followed by beta-blockers. Alpha-blockers are less likely to cause problems.
- Antidepressants: SSRIs and older tricyclic antidepressants frequently affect sexual function. This includes widely prescribed drugs for depression and anxiety.
- Anti-anxiety medications: Benzodiazepines, commonly prescribed for anxiety and insomnia, can suppress arousal.
- Antihistamines: Both allergy medications and certain heartburn drugs (H2 blockers) can contribute.
- Hormonal treatments: Drugs that block or suppress testosterone, often used for prostate cancer, reliably cause ED.
- Hair loss and prostate medications: Finasteride and dutasteride, used for male pattern baldness and enlarged prostate, affect hormone pathways that can impair erections.
Never stop a prescribed medication without talking to your doctor first. In many cases, switching to a different drug in the same class can resolve the issue.
Weight, Smoking, and Lifestyle
Body weight is one of the strongest modifiable predictors of ED severity. In research examining the combined effects of lifestyle factors, BMI was a stronger predictor of severe ED than either smoking or alcohol use. Each unit increase in BMI raised the odds of severe ED by about 21%. Excess weight damages blood vessels, promotes inflammation, lowers testosterone, and increases the risk of diabetes, all of which independently contribute to erection problems.
Smoking damages the endothelium directly and accelerates atherosclerosis. Smokers are significantly more likely to experience severe ED than nonsmokers. The damage is cumulative, meaning the longer and more heavily you smoke, the greater the impact, but quitting does allow some vascular recovery over time.
Alcohol’s relationship with ED is more nuanced. Chronic heavy drinking can damage nerves, suppress testosterone, and cause liver disease, all of which contribute to ED. But moderate drinking hasn’t shown a clear statistical link to increased ED severity in research.
Psychological and Emotional Causes
ED isn’t always rooted in a physical problem. Stress, anxiety, depression, and relationship conflict can all interfere with arousal. Performance anxiety is especially common in younger men: one episode of difficulty leads to worry about the next time, which makes the problem worse, creating a self-reinforcing cycle.
Depression deserves special mention because it works on both sides. Depression itself reduces libido and disrupts the brain chemistry involved in arousal. And antidepressants used to treat it frequently cause ED as a side effect. This double impact makes ED particularly common among men with depression.
In practice, psychological and physical causes often overlap. A man with mildly reduced blood flow might function fine until work stress tips the balance. Addressing both sides typically produces better results than focusing on just one.