At its core, ED is caused by a deficit in NO release, cyclic GMP (cGMP) and calcium signaling, or smooth muscle relaxation. However, many overlapping mechanisms can interrupt this signaling cascade.
Psychogenic or sympathetic-mediated ED is caused by stress, depression, or anxiety about sexual performance. Neurogenic ED is caused by a deficit in nerve signaling to the penis, which may be secondary to spinal cord injury, traumatic brain injury, or surgery. Vasculogenic ED — the most common form of ED — is caused by underlying vascular disease, endothelial dysfunction, and structural changes to the arterial walls. Iatrogenic ED is most often the result of pelvic surgery or the use of medications. Finally, endocrine causes of ED include low levels of androgens (e.g., testosterone) and other hormones.
A number of medications have been linked to ED, including antihypertensives (blood pressure medications); 5𝛼-reductase inhibitors, anti-androgens, luteinizing hormone-releasing agonists and antagonists (used to treat prostate cancer), antidepressant medications, and opiates.[1]