Erectile Dysfunction: The 4 Causes Behind Almost Every Case

Last updated: August 15, 2026

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Erectile dysfunction is one of the most common concerns men bring to my clinic — and it arrives far younger than most people expect. I regularly see patients in their twenties. The formal definition is the persistent inability to attain and maintain an erection sufficient for satisfactory sexual performance, and the word that matters in it is persistent: an occasional off night is not erectile dysfunction.

ED carries more weight than most men realise. It affects more than 50% of US men aged 40 and over, and recent literature finds that 25% of new cases occur in men under 40. It reshapes relationships. And, most importantly, it can be an early warning of cardiovascular disease — the penile arteries are narrow, so they clog before the coronary arteries do, which means ED often appears years before a heart problem announces itself.

The 4 causes of erectile dysfunction

Working out which of these applies is the whole point of the first consultation, because the four are treated in completely different ways.

1. Hormonal — low testosterone

Testosterone is the central male sex hormone. Levels peak around age 20 and decline gradually thereafter. Low testosterone shows itself as low desire, fatigue, flat mood and reduced energy — often before the erections themselves change. The standard test is a blood testosterone level taken in the early morning, when levels are at their highest; a sample taken in the afternoon can read falsely low. Replacement therapy helps men with confirmed deficiency, though it needs more careful thought in younger men who may still want children.

2. Neurogenic — the nerve pathway

An erection is a reflex that runs from the brain, down the spinal cord, to the penis. Anything that interrupts that path can break it: stroke, Parkinson’s disease, spinal cord injury, and the nerve damage that comes with long-standing diabetes. This is the most difficult group to treat, because the wiring itself is damaged rather than the plumbing.

3. Vasculogenic — blood supply

This is the big one: poor blood vessel quality accounts for around 75% of all ED. An erection is, mechanically, a question of getting enough blood in and keeping it there — so anything that damages arteries damages erections. Smoking is the clearest culprit, harming vessels throughout the body and the small penile arteries especially. Obesity, hypertension, diabetes and high cholesterol all belong in the same group, and all of them are controllable.

That 75% figure is also why ED deserves to be taken seriously as a general health signal rather than treated as a purely sexual complaint. Three quarters of the time, it is telling you something about your blood vessels.

4. Psychological

Work pressure, family responsibility and the ordinary weight of daily life all affect sexual function directly, and this cause is disproportionately common in younger men. It also feeds itself: one difficult episode creates anxiety about the next, and the anxiety does the rest. The encouraging side is that the same lever works in reverse — better sleep, regular exercise and time spent on things you enjoy measurably improve psychogenic ED.

What to do next

In practice these four rarely arrive alone — a man in his fifties with untreated hypertension who smokes and is anxious about it has three of them at once, and treating only one will disappoint everybody. That is why the assessment matters more than the prescription.

Understanding the cause is only the first step. For the full diagnostic workup and the complete range of treatments — oral therapy, shockwave therapy, injections and penile implants — see erectile dysfunction treatment in Bangkok.

If you are experiencing erectile dysfunction or suspect low testosterone and would like a confidential specialist evaluation, Dr. Soarawee Weerasopone offers consultations at Bangkok Hospital Headquarters. Book a Consultation. Appointments at Samitivej Sriracha Hospital can be arranged by calling the Urology department on 088-022-1445.

Frequently Asked Questions about Erectile Dysfunction

Disclaimer: This content is written and reviewed by Dr. Soarawee Weerasopone, a board-certified urologist at Bangkok Hospital Headquarters. It is intended for educational purposes only and does not constitute medical advice. No medical advice, diagnosis or prescription is provided through personal messaging channels. Always consult a qualified healthcare professional before starting any medical treatment.