Erectile dysfunction: causes, the blood tests that matter, and treatment

Erectile dysfunction (ED), once called impotence, is one of the most common reasons men see a doctor. The penis depends on small arteries, steady nerve signals and enough testosterone, so erection problems often show up early when any of those starts to fail. In the Massachusetts Male Aging Study, 52% of men aged 40 to 70 reported some degree of ED: 17% minimal, 25% moderate and 10% complete ². Tablets restore erections in many men, and blood tests find the cause behind them, often narrowed arteries, high blood sugar or low testosterone.

What erectile dysfunction is

Erectile dysfunction is a persistent difficulty getting an erection, or keeping one long enough, for satisfying sex. Doctors usually look for a pattern that has lasted at least three months. A bad night after drinking, during a stressful week or with a new partner is ordinary and does not count.

ED becomes more common with age, but age alone is rarely the full explanation. The conditions that build up with age (narrowed arteries, raised blood sugar, high blood pressure, falling testosterone, more prescription medicines) are what damage erections, which is why the workup looks for them.

How an erection works, and where it breaks

Most cases come from one or more of five sources, and stress, anxiety and relationship strain can sit on top of any of them. The NHS lists high blood pressure, high cholesterol, diabetes, depression, anxiety and hormone problems among the common causes ¹.

Is it physical or psychological? The morning erection clue

Healthy men have erections during sleep, several times a night, and often wake with one. Those night-time erections run on the same blood vessels and nerves but bypass performance pressure. If morning erections are still firm, the hardware is usually working, which points toward a psychological cause. If they have faded along with erections during sex, a physical cause is more likely. Erections that get weaker gradually, in every situation, usually point to the blood vessels rather than to stress.

The clue suggests a likely cause but cannot confirm it. Physical and psychological causes also feed each other: a man whose erections weaken because of narrowing arteries soon starts to worry about sex, and that performance anxiety makes erections worse still. If worry and low mood are part of the picture, the page on anxiety covers what helps.

Why erectile dysfunction can be an early warning for the heart

The penile arteries are about 1 to 2 mm across, against 3 to 4 mm for the coronary arteries that feed the heart. The artery-size hypothesis holds that the same slow build-up of plaque restricts flow in the smaller vessel first, so ED often comes before heart symptoms, typically by two to three years ¹¹. A meta-analysis of 14 prospective studies covering about 92,000 men found that ED was linked to a higher risk of every major cardiovascular outcome ³.

In a long-running community study, the link was strongest in younger men, those in their 40s ¹². The Princeton III consensus advises that every man with ED, even without heart symptoms, has his cardiovascular risk assessed ¹³: blood pressure, blood sugar, cholesterol, smoking and waist size. Our heart health hub explains how those pieces add up to a risk score.

Which blood tests to get for erectile dysfunction

The British Society for Sexual Medicine recommends the same core set for every man with ED: a measure of blood sugar (HbA1c or fasting glucose), a lipid panel and a morning total testosterone ⁶. Other tests are added when the history or the first results point to them.

Reading your testosterone result

Testosterone peaks in the morning and can drop after a meal, so the Endocrine Society advises a fasting morning sample and a repeat before anyone diagnoses low testosterone ⁵. A single low result after a late night, an illness or a big breakfast is common and often normal on the second test. The Endocrine Society uses 264 ng/dL (9.2 nmol/L) as the lower limit for healthy young men ⁵. The British Society for Sexual Medicine treats levels under 8 nmol/L (about 230 ng/dL) as clearly low and 8 to 12 nmol/L (about 230 to 350 ng/dL) as a grey zone where symptoms decide ⁶. If your lab uses the other unit, the testosterone converter switches between ng/dL and nmol/L.

CalculatorFree testosterone calculatorGot total testosterone, SHBG and albumin (a common blood protein on most chemistry panels) on one report? Turn them into a free testosterone.Work it out

Low testosterone tends to lower sex drive more than it weakens erections directly. Testosterone therapy improves desire in men with confirmed low levels, but its effect on erections is modest, so it is offered when a deficiency is confirmed rather than as a general ED treatment ⁵. Some men with low testosterone and ED are prescribed a PDE5 inhibitor alongside it; that is a decision for their doctor. Symptoms and treatment are covered on the low testosterone page, and TRT blood work lists the monitoring tests if therapy starts.

Reading your blood sugar and cholesterol results

Diabetes damages erections twice over, through the nitric oxide signal in artery walls and through the nerves that start an erection. A meta-analysis of 145 studies found ED in about half of men with diabetes, with more than three times the odds seen in men without diabetes ¹⁰. ED is sometimes the first symptom that leads to a diabetes diagnosis. An HbA1c in the prediabetes range is worth acting on early, and an HbA1c of 6.5% or higher is in the diabetes range and should be confirmed and managed with your doctor. For men who already have type 2 diabetes, tighter glucose and blood pressure control protect the small vessels that erections depend on.

On a lipid panel, the results that matter most for arteries are LDL cholesterol, non-HDL cholesterol and triglycerides. Apolipoprotein B (ApoB) counts the cholesterol-carrying particles directly, and it can run high when LDL looks fine; ApoB vs LDL explains when the two disagree, and high ApoB covers what a raised count means. When ED may be signalling vessel trouble, that is a good reason to go over cholesterol and overall heart risk with a doctor.

Next step: if your HbA1c is 5.7% or higher, or your LDL or ApoB is above your lab's range, ask your doctor for a cardiovascular risk assessment and a plan, then recheck HbA1c and a lipid panel about 3 months after any change in diet, exercise or medicine.

Sudden ED, and ED in your 20s and 30s

Erectile dysfunction that appears over days or weeks usually has a trigger: a new medicine, a stressful event, heavy drinking, recreational drugs, a recent illness or a relationship change. Look at what changed in the month before. If a new prescription medicine is the likely trigger, raise it with the prescriber rather than stopping it yourself. Sudden ED with low desire, new headaches, vision changes or breast swelling can point to high prolactin from a pituitary problem and needs a prompt doctor's appointment, not only a blood test. Men who use or have recently stopped anabolic steroids, which shut down the body's own testosterone production, should also have their hormones checked.

ED is not only a problem of older men: at one Italian clinic, about one in four men newly diagnosed with ED was under 40 ⁹. Psychological causes are more common in younger men, but physical causes are found often enough that the same basic checks apply. Smoking, heavy cannabis use, poor sleep and very low body fat from extreme training are worth raising with a doctor.

Treatment: what works and how well

Treatment starts with the cause. That can mean getting blood pressure, blood sugar or cholesterol under control, or switching a medicine that is known to affect erections, which is always done with the prescriber and never by stopping a drug on your own. In men who already need a statin for their heart, a meta-analysis of randomized trials found a small improvement in erectile function scores ⁷; statins are not prescribed for ED itself.

1. 1First line: PDE5 inhibitorsSildenafil (Viagra), tadalafil (Cialis), vardenafil and avanafil help many men ⁶. They work only with sexual arousal, and they differ mainly in how fast they start and how long they last. A doctor or pharmacist checks your heart and your other medicines first.
2. 2Second line: devices and local treatmentsVacuum erection devices, alprostadil as a urethral pellet or cream, and injections into the side of the penis work without the nitric oxide pathway, so they can help when tablets fail.
3. 3Third line: penile implantsAn inflatable implant, placed by a urologist, is an option when other treatments have not worked, and most men who have one report being satisfied ⁶.
4. 4Alongside any of these: psychosexual therapyCognitive behavioral therapy or sex therapy, ideally with a partner, treats performance anxiety and helps men return to sex confidently after a long gap.

Two amino acid supplements have been studied in mild ED. In a small trial of 24 men, more reported harder erections on L-citrulline than on placebo ¹⁴, and a 2019 meta-analysis of small trials found L-arginine improved erectile function scores in mild to moderate ED compared with placebo ¹⁵. The trials were small, neither supplement has been shown to work as well as prescription tablets, and neither replaces finding the cause. Check with your doctor before trying one, especially if you take blood pressure medicines.

What you can change yourself

The strongest evidence for lifestyle change comes from a randomized trial of 110 obese men with ED who spent two years losing weight and exercising more ⁴. The changes that helped erections were the same changes that lower heart risk.

• Lose weight if your waist is large: belly fat lowers testosterone and drives metabolic syndrome.
• Exercise most days, with both aerobic work and strength training.
• Stop smoking, which damages the artery lining that makes nitric oxide.
• Keep alcohol to two drinks a day or fewer, and avoid drinking heavily before sex.
• Get blood pressure checked and treated: the high blood pressure page covers targets.
• Sleep seven to nine hours; short sleep and untreated sleep apnea lower testosterone.
• Try pelvic floor exercises, which helped men keep erections in a randomized trial ¹⁶.
• If you cycle long distances, use a saddle that takes pressure off the area behind the scrotum.

For the hormone side of this list, how to increase testosterone covers which habits move testosterone and by how much.

When to see a doctor

See a doctor if erection problems have lasted more than a few weeks or keep coming back. Doctors discuss ED every day. A short visit usually covers blood pressure, pulse and waist, a genital or prostate examination depending on age and symptoms, and the three core blood tests. Depending on the results you may be referred to urology, endocrinology, cardiology or a psychosexual therapist. Bring a list of every medicine and supplement you take.

• Go sooner if ED comes with chest pain, breathlessness on exertion or calf pain on walking.
• Go sooner if ED comes with low libido, tiredness, breast swelling, headaches or changes in vision, which can point to a hormone or pituitary problem.
• Go sooner if erections have become painful or bent, which can be Peyronie's disease.
• An erection lasting more than 4 hours (priapism) is an emergency: go to the emergency department, even if it is not painful.

Free, no accountRead your blood testAlready have a lipid panel, HbA1c or testosterone result? Read every line of it, free, before your appointment.Read my results

Free, no accountDrop in your lab report and see every marker explained in plain words, placed on the body, against your lab's range. It's read on your device: nothing is uploaded and nothing is kept.

Read my results Download the app