Thanks for your question, Frightened Turtle! To help answer it, we spoke with Dr. Darius Paduch, urologist and male sexual medicine specialist at New York Presbyterian/Weill Cornell Medical Center, and sex therapist Jenni Skyler, Ph.D., director of The Intimacy Institute for sex and relationship therapy in Boulder, Colorado. Here's what they had to say:
In their extensive review, Bassil and coworkers summarise the benefits and risks, with benefits such as improvement of sexual function, bone density, muscle strength, cognition and overall improvement in quality of life. Among the risks that have been suggested include erythrocytosis, liver toxicity, worsening of sleep apnoea and cardiac function, possibly increasing symptoms of benign prostatic hyperplasia (BPH). They also note that although a possibility of stimulation of prostate cancer has been hypothesised, no scientific or clinical evidence exists to this possible risk.38
Hypogonadism may be suggested by the patient's general appearance. If testosterone deficiency antedates puberty, as in Klinefelter's syndrome, eunuchoid proportions—defined as an arm span 5 cm or more in excess of height, or a sole-to-pubis length exceeding crown-to-pubis length by more than 2 cm—may be present. In postpubertal males whose testosterone levels are markedly depressed, the secondary sexual characteristics may become atrophic. Testicles less than 4 cm in length or a prostate gland that is smaller than expected may be the only clues on physical examination to a pituitary tumor with secondary hypogonadism.
Performance anxiety can be another cause of impotence. If a person wasn’t able to achieve an erection in the past, he may fear he won’t be able to achieve an erection in the future. A person may also find he can’t achieve an erection with a certain partner. Someone with ED related to performance anxiety may be able to have full erections when masturbating or when sleeping, yet he isn’t able to maintain an erection during intercourse.
Traditionally, erectile impotence (the classical definition of impotence) is the failure to achieve penile erection during intercourse. It may have either physical or psychological causes. Alcoholism, endocrine disease, and neurological disorders are typical physical causes. Psychological causes include anxiety over performance, hostility or other negative feelings toward the sexual partner, and stress, anxiety, depression, or other emotional conflicts outside of the relationship. Erectile impotence occasionally occurs with age and, although attributed by the individual to the aging process itself, it is usually secondary to disorders of aging, such as faulty blood circulation or prostate disease. In cases of impotence caused by blood vessel dysfunction, an insufficient supply of blood flows into the penis, or the blood diffuses out into adjacent tissues.
An analysis of 14 studies involving more than 90,000 patients with ED confirmed the relation between ED and an increased risk of cardiovascular events and mortality.  Compared with patients without ED, those with ED had a 44% increased risk of cardiovascular events, a 25% increased risk of all-cause mortality, a 62% increased risk of MI, and a 39% increased risk of cerebrovascular events. Treatment of ED, either through lifestyle interventions or by pharmacologic means, may improve prognosis and reduce risk.
The link between chronic disease and ED is most striking for diabetes. Men who have diabetes are two to three times more likely to have erectile dysfunction than men who do not have diabetes. Among men with erectile dysfunction, those with diabetes may experience the problem as much as 10 to 15 years earlier than men without diabetes. Yet evidence shows that good blood sugar control can minimize this risk. Other conditions that may cause ED include cardiovascular disease, atherosclerosis (hardening of the arteries), kidney disease, and multiple sclerosis. These illnesses can impair blood flow or nerve impulses throughout the body.