Erectile Dysfunction Education

Vasculogenic ED — The Most Common Cause

Arteriogenic (vasculogenic) ED — reduced penile arterial blood flow due to endothelial dysfunction and atherosclerosis — accounts for more than 50% of ED cases, and this proportion increases with age. The pathophysiology is identical to peripheral and coronary artery disease: progressive endothelial dysfunction reduces NO bioavailability, increases oxidative stress, and leads to lipid plaque deposition. Because penile arteries are smaller (diameter 1–2 mm) than coronary arteries (~3–4 mm), they develop hemodynamically significant stenosis earlier in the same disease process.

Major modifiable vascular risk factors for ED include: diabetes mellitus (2–4x increased ED risk), hypertension, dyslipidemia, smoking, obesity, and sedentary lifestyle.

Hormonal ED

Testosterone is essential for normal erectile function: it maintains libido, stimulates expression of NO synthase in cavernous tissue, supports the structural health of smooth muscle and connective tissue in the corpora cavernosa, and maintains sensitivity of androgen receptors in the penis. Testosterone deficiency produces ED primarily through reduced libido and impaired cavernous smooth muscle responsiveness. Hypogonadism is the primary cause of ED in approximately 5–10% of cases, but contributes as a secondary factor in many more. Other hormonal contributors: hyperprolactinemia, thyroid dysfunction, and elevated estradiol.

Neurogenic ED

Intact cavernous nerve innervation is required for the initial NO-mediated smooth muscle relaxation that initiates erection. Major neurogenic ED causes: diabetic autonomic neuropathy (affects ~35–75% of men with long-duration diabetes), radical prostatectomy, spinal cord injury, and multiple sclerosis. Neurogenic ED is characterized by absent nocturnal penile tumescence (NPT), distinguishing it from psychogenic ED.

Medication-Induced ED

Multiple commonly prescribed drug classes impair erectile function: beta-blockers, thiazide diuretics, SSRIs and SNRIs, antipsychotics, and 5α-reductase inhibitors (finasteride, dutasteride). Medication review is a standard component of every ED evaluation — drug-induced ED may be fully reversible with medication adjustment.

Step 1 — Lifestyle Modification (All Patients)

The JAMA trial (Esposito K et al., 2004) randomized 110 obese men with ED to intensive lifestyle intervention (Mediterranean diet, caloric restriction, aerobic exercise 195 min/week) or general health counseling. At two years, the intervention group showed significant improvement in IIEF scores (+7.0 vs. +1.7 in controls) and 31% of intervention men recovered normal erectile function (IIEF-5 > 21) vs. only 5% of controls. Meta-analysis (Silva AB et al., BJSM, 2017) confirmed aerobic exercise significantly improves IIEF scores — recommended protocol: 40 minutes of moderate-to-vigorous aerobic exercise, 4 times/week.

Step 2 — PDE5 Inhibitors (First-Line Pharmacotherapy)

The four FDA-approved PDE5 inhibitors have collectively been evaluated in hundreds of RCTs. Overall response rates (60–80%) reflect efficacy across ED etiologies. PDE5 inhibitors require intact NO production to work — in men with severe vascular disease or nerve damage, response rates are lower. They are absolutely contraindicated with any nitrate medication. Generic versions of sildenafil and tadalafil have dramatically reduced cost and are bioequivalent to brand products.

Step 3 — Testosterone Optimization Where Indicated

For men with confirmed hypogonadism (< 300 ng/dL with consistent clinical symptoms), testosterone therapy addresses both the root hormonal cause and improves PDE5 inhibitor response. Meta-analysis by Isidori AM et al. (European Journal of Endocrinology, 2014) found TRT significantly improved sexual desire, erectile function, and IIEF scores in hypogonadal men. Testosterone therapy has been shown to rescue PDE5 inhibitor response in men who had failed oral therapy while testosterone-deficient.

Step 4 — Trimix Intracavernosal Injection (Second Line)

For men who do not achieve adequate response to an appropriate trial of PDE5 inhibitors, Trimix intracavernosal injection is the evidence-based second-line option per AUA guideline. Trimix produces erection through a mechanism entirely independent of NO production, making it effective even when PDE5 inhibitors fail. See our dedicated Trimix Overview page.