Some common medicines produce impotence as a side effect. Smoking affects blood flow in veins and arteries, and is also believed to lead to impotence. Psychological factors such as stress, anxiety, guilt, depression, low self-esteem, and fear of sexual failure are associated with impotence. If the underlying condition leading to impotence cannot be corrected, or if impotence problems persist, medications can help certain men achieve erection sufficient for sexual Intercourse as well as maintain erection after penetration. The penis contains two chambers, called the corpora cavernosa, which run the length of the organ.
Erection begins with sensory and mental stimulation.
Impulses from the brain and local nerves cause the muscles of the corpora cavernosa to relax, allowing blood to flow in and fill the chambers. The inflow of blood creates pressure in the corpora cavernosa chambers, making the penis expand. Erection is reversed when muscles in the penis contract, stopping the inflow of blood and causing the blood in the chambers to flow out. Cyclic GMP is a natural enzyme responsible for smooth muscle relaxation of the corpora cavernosa, and the trapping of blood necessary for erection. Degradation of cyclic GMP by an enzyme PDE5 lowers the cyclic GMP levels, causing outflow of blood from the chambers and loss of erection.