| Smoking | High | Endothelial damage → reduced NO production. Penile atherosclerosis. Boston U 1998: smokers had measurably shorter erect length. Leading modifiable ED cause. | Partially (2-5 years post-cessation) |
| Diabetes mellitus | Very High | Triple assault: peripheral neuropathy (nerve damage), endothelial dysfunction, hormonal disruption. 50-75% of diabetic men develop ED. | Partially with glycemic control |
| Obesity (BMI >30) | Moderate-High | Reduced testosterone (aromatization to estrogen in fat), endothelial dysfunction, systemic inflammation, buried penis appearance. | Yes with weight loss |
| Chronic alcohol | Moderate | Peripheral neuropathy, liver damage (impaired hormone metabolism), direct gonadal toxicity. Acute: CNS depressant. | Partially with abstinence |
| SSRIs (antidepressants) | Moderate-High | Serotonin inhibits dopamine and NO pathways. 30-70% of SSRI users report sexual dysfunction. Bupropion has lowest risk. | Yes with dose reduction/switch |
| Beta-blockers | Moderate | Reduce cardiac output, impair sympatholytic relaxation. Nebivolol is exception (promotes NO release). | Yes with medication change |
| Performance anxiety | Moderate | Sympathetic activation releases norepinephrine → cavernosal artery constriction, opposing parasympathetic erection. Self-perpetuating cycle. | Yes with CBT/therapy |
| Sleep deprivation | Moderate | Testosterone drops 10-15% after 1 week of 5h/night sleep (Leproult 2011, JAMA). Reduces NPT episodes. Impairs endothelial function. | Yes with sleep restoration |
| Sedentary lifestyle | Moderate | Reduced cardiovascular fitness = reduced penile blood flow. 30 min/day moderate exercise reduces ED risk by 40% (multiple meta-analyses). | Yes with exercise |
| Opioids | Moderate-High | Suppress GnRH → hypogonadism. Prevalence of ED in chronic opioid users: 50-85%. | Often yes with cessation/dose reduction |