Erectile dysfunction is not a diagnosis. It is a symptom, in the same way that breathlessness is a symptom. The useful clinical question is never "does this man have ED" but "why does this man have ED", because the answer determines whether the right response is a tablet, a change of blood pressure medication, better diabetic control, a course of therapy, or an urgent cardiac review.

This article works through the causes of erectile dysfunction in detail: how each one interrupts the erectile process, what clues point to it, and which are reversible. If you want the broader overview of what ED is and how it is treated, start with our guide to erectile dysfunction.

The chain that has to work

An erection depends on a sequence, and each cause of ED breaks a specific link in it.

Desire and central signalling. The brain initiates arousal. Testosterone, dopamine and mood all feed into this step.
Nerve conduction. Signals travel down the spinal cord and through the pelvic nerves to the penis.
Nitric oxide release. Nerve endings and the endothelium, the inner lining of the blood vessels, release nitric oxide.
Smooth muscle relaxation and arterial inflow. The arteries dilate and blood floods the erectile chambers.
Veno-occlusion. The expanding chambers compress the draining veins, trapping blood and producing rigidity.

Categorising causes by which step they break makes the whole subject far easier to navigate.

Vascular causes: the largest group

Somewhere between sixty and seventy percent of ED in men over forty is primarily vascular. Two distinct mechanisms sit inside this category.

Arterial insufficiency

Atherosclerosis narrows arteries throughout the body. Because the penile arteries are among the smallest in the arterial tree, at roughly one to two millimetres, they lose functional capacity earlier than the coronary or carotid arteries. Inflow drops, and the chambers never fill fast enough to produce full rigidity.

The drivers are the familiar cardiovascular risk factors: high LDL cholesterol, raised Lipoprotein(a), hypertension, smoking, diabetes and inactivity. This is why new ED should always prompt a cardiac risk assessment. Symptoms typically come on gradually over years, affect every situation, and are accompanied by a decline in morning erections.

Venous leak

Less common and often missed. Here the arteries deliver enough blood but the veno-occlusive mechanism fails to trap it, so the erection builds and then fades quickly, often within a minute or two of stopping stimulation. It can follow fibrosis of the erectile tissue from ageing, diabetes, or Peyronie's disease, and it is one of the reasons a man may respond poorly to PDE5 inhibitors. Diagnosis requires penile Doppler ultrasound.

Endothelial dysfunction

Before any plaque is visible, the endothelium can lose its ability to produce nitric oxide on demand. This is the earliest stage of vascular disease and it is a common finding in men in their thirties and forties with metabolic syndrome. It is also, encouragingly, the stage most responsive to exercise, weight loss and smoking cessation.

Metabolic causes

糖尿病

Diabetes is the single most consequential medical cause of ED. Roughly half of men with diabetes develop erectile dysfunction, typically ten to fifteen years earlier than men without it, and the ED tends to be more severe and less responsive to tablets. This matters a great deal in Singapore, where the national burden of diabetes is high and where a significant proportion of men with the condition are unaware they have it.

Diabetes attacks the erectile mechanism from three directions at once. It damages the small blood vessels, reducing inflow. It damages the autonomic nerves, blunting nitric oxide release. And it drives fibrosis within the erectile tissue, contributing to venous leak. It is also associated with lower testosterone. Good glycaemic control slows all four processes, which is why ED assessment and diabetes care belong together.

Obesity and metabolic syndrome

Excess visceral fat causes ED through several independent routes: chronic low-grade inflammation that damages the endothelium, insulin resistance, and the conversion of testosterone into oestradiol by the aromatase enzyme present in fat tissue. In Singapore the relevant thresholds are lower than the international ones, with health authorities here recommending a body mass index cutoff of 23 for increased risk in Asian populations rather than 25.

The good news is that this category is highly reversible. Trials of intensive lifestyle intervention in obese men with ED have shown clinically meaningful improvement in erectile function with sustained weight loss.

Obstructive sleep apnoea

Frequently overlooked. Repeated overnight oxygen dips damage the endothelium, disrupt the nocturnal testosterone surge that normally occurs during deep sleep, and produce the daytime fatigue that flattens libido. Any man with ED who snores heavily, wakes unrefreshed or has been told he stops breathing at night should be assessed for it.

Hormonal causes

Low testosterone

Testosterone maintains libido, supports nitric oxide production and preserves the health of the smooth muscle in the erectile chambers. Genuinely low levels reduce sexual interest first and erectile quality second. Diagnosis requires a morning sample, ideally before eleven, repeated on a separate day, interpreted alongside symptoms rather than in isolation. Our overview of testosterone deficiency covers the assessment in full.

An important caveat: low testosterone is a less common sole cause of ED than the marketing around it suggests. Many men with borderline levels have vascular ED, and treating the hormone alone leaves them disappointed. Equally, obesity lowers testosterone, so the low reading is sometimes a consequence of the same problem driving the ED rather than its root.

Thyroid disorders

Both underactive and overactive thyroid can impair erectile function and libido, and both are simple to test and treat.

Raised prolactin

High prolactin suppresses testosterone and blunts libido. It can be caused by a benign pituitary tumour or by medications, particularly some antipsychotics. It should be checked in any man with low libido alongside ED.

Neurological causes

Anything that interrupts the nerve pathway between brain and penis can cause ED.

Pelvic surgery. Radical prostatectomy is the classic example. Nerve-sparing technique and early penile rehabilitation improve outcomes considerably.
Spinal cord injury and disc disease. Effects depend on the level and completeness of the lesion.
Multiple sclerosis and Parkinson's disease. Both commonly involve sexual dysfunction, sometimes as an early feature.
Diabetic autonomic neuropathy. Discussed above, and the most common neurological contributor overall.
Cycling. Prolonged pressure on the perineum from a narrow saddle can compress the pudendal nerve and its accompanying artery. It is usually reversible with a wider or cut-out saddle, correct bike fit and regular standing breaks.

Medication-induced erectile dysfunction

This category deserves more attention than it gets, because the fix can be as simple as a substitution.

Drug class	Examples	Mechanism
Older beta-blockers	Propranolol, atenolol	Reduced sympathetic tone and peripheral blood flow
Thiazide diuretics	Hydrochlorothiazide	Reduced penile blood flow, mechanism incompletely understood
SSRIs and SNRIs	Fluoxetine, sertraline, venlafaxine	Serotonergic suppression of libido, delayed ejaculation, ED
5-alpha reductase inhibitors	Finasteride, dutasteride	Reduced dihydrotestosterone; taken for hair loss and prostate enlargement
Antipsychotics	Risperidone and others	Raised prolactin, dopamine blockade
Anti-androgens	Used in prostate cancer therapy	Direct hormonal suppression

Two points. First, never stop a prescribed medication yourself, particularly cardiovascular or psychiatric drugs. Second, alternatives usually exist. Newer vasodilating beta-blockers such as nebivolol are much less associated with ED, ACE inhibitors and ARBs are broadly neutral, and among antidepressants some agents carry a considerably lower sexual side effect burden. This is a conversation to have with your doctor, not a reason to abandon treatment.

Lifestyle and substance causes

Smoking is directly toxic to the endothelium and roughly doubles the risk of ED. It is also one of the few causes where quitting produces measurable improvement, particularly in younger men and within the first year. Our article on what changes when you quit smoking covers the timeline.

Alcohol in the short term depresses the central nervous system and impairs performance. Sustained heavy use damages nerves, lowers testosterone and impairs liver function.

Recreational drugs, including cannabis, stimulants and opioids, all impair erectile function through different mechanisms. Anabolic steroid use is a particular problem in gym culture: exogenous testosterone shuts down the body's own production, and men often present with ED, testicular shrinkage and impaired fertility after stopping.

Chronic sleep deprivation lowers testosterone measurably. Studies have shown a meaningful drop in daytime testosterone in healthy young men after a week of restricted sleep.

Psychological causes

Psychological factors are rarely the whole story in older men and are frequently the whole story in younger ones.

Performance anxiety creates a self-sustaining loop. One failure produces anticipatory anxiety, anxiety triggers sympathetic nervous system activation, and sympathetic activation directly opposes the parasympathetic signalling required for an erection. The fear of failure becomes the mechanism of failure.

Depression reduces libido through the illness itself and, awkwardly, through the medications used to treat it. The relationship is bidirectional: ED raises the risk of depression, and depression raises the risk of ED. Our article on ED and mental health explores this in depth.

Relationship factors including unresolved conflict, loss of intimacy and mismatched expectations are common and often unspoken.

Stress. Sustained work pressure keeps the sympathetic nervous system in a state that is physiologically incompatible with arousal.

Pornography-related concerns. A subject with more heat than evidence. What is reasonably well supported is that some men develop conditioned arousal patterns and unrealistic expectations that make partnered sex harder. Men who present with normal solo erections and consistent partnered difficulty, with no risk factors, sometimes fall into this group.

Working out which cause applies to you

Certain patterns are informative.

Gradual onset, absent morning erections, present in all situations, risk factors present. Points strongly to vascular or metabolic causes.
Sudden onset, preserved morning erections, situational. Points to a psychological cause.
Onset within weeks of starting a new medication. Points to the drug.
Low libido as the dominant feature, with fatigue and reduced muscle mass. Points to a hormonal cause.
Rapid loss of an erection once achieved. Raises the question of venous leak.
Pain or new curvature. Points to Peyronie's disease.

None of these is diagnostic on its own, which is the argument for a structured assessment: history, examination, and blood tests covering glucose, HbA1c, lipids, morning testosterone, thyroid function and prolactin. A full health screening covers most of this in a single fasting visit.

Which causes are reversible

Cause	Reversibility	What helps
Medication-induced	High	Substitution under medical supervision
Psychogenic	High	Therapy, treating anxiety or depression, partner involvement
Smoking-related	Moderate to high	Cessation, best results in younger men
Obesity and metabolic	Moderate to high	Weight loss, exercise, glycaemic control
Low testosterone	Moderate	Weight loss first, replacement where genuinely indicated
Sleep apnoea	Moderate	Diagnosis and treatment of the apnoea
Established atherosclerosis	Low to moderate	Risk factor control, PDE5 inhibitors, shockwave therapy
Venous leak	Low	Injections, vacuum device, implant in severe cases
Post-surgical nerve injury	Variable	Early penile rehabilitation

Getting to the cause in Singapore

Hisential sees men from every part of Singapore for erectile dysfunction assessment, and the emphasis is on identifying the cause rather than handing over a prescription. A first appointment covers history, examination and the relevant blood panel, with results reviewed together and a plan built around what the tests actually show. Consultation is from S$50 after GST before investigations. The clinic sits on Orchard Road, minutes from Orchard MRT, and follow-up reviews can usually be done remotely.

Frequently asked questions

Can erectile dysfunction have more than one cause?

In most men over forty it does. A typical picture is mild vascular disease, a degree of insulin resistance, one contributing medication and a layer of performance anxiety built on top. Treating only one of the four rarely produces a satisfying result.

Does ED always mean I have heart disease?

No, but it raises the probability enough to justify checking. Studies following men with new ED have consistently found elevated rates of subsequent cardiac events, typically appearing three to five years later. That window is the reason to investigate now rather than wait.

Can stress alone cause erectile dysfunction?

Yes. Sustained stress keeps the sympathetic nervous system dominant, and sympathetic activation directly opposes the signalling an erection requires. Stress-driven ED usually has an identifiable start point and preserved morning erections.

I am in my twenties. Why do I have ED?

In younger men the common contributors are anxiety and performance pressure, sleep deprivation, heavy alcohol or drug use, anabolic steroid use, and increasingly early metabolic disease. Younger men still deserve a proper assessment, because occasionally ED at this age is the first sign of a hormonal or vascular problem.

Will changing my blood pressure medication fix my ED?

It can help substantially if the drug is a contributor, particularly with older beta-blockers or thiazide diuretics. It is not a decision to make alone. Bring it to your doctor, who can weigh the alternatives against your cardiovascular risk.

How long does it take for lifestyle changes to improve erections?

Expect months, not weeks. Trials of exercise and weight loss interventions typically show measurable improvement in erectile function scores over three to six months of sustained change.

References

Health Promotion Board Singapore, Asian body mass index guidance and diabetes prevention resources.
Singapore Ministry of Health, National Population Health Survey.
European Association of Urology, Guidelines on Sexual and Reproductive Health.
Esposito K et al., Effect of lifestyle changes on erectile dysfunction in obese men, randomised controlled trial.
Leproult R, Van Cauter E, Effect of sleep restriction on testosterone levels in young healthy men.

勃起不全（ED）の原因とは？