In the past 6 years, the FDA has approved three oral agents for the treatment of ED: sildenafil, vardenafil, and tadalafil. All three are phosphodiesterase type 5 (PDE-5) inhibitors and work by potentiating the effect of nitric oxide in the penis. In particular, they block the hydrolysis of cyclic guanosine monophosphate to guanosine 5'-monophosphate, thus enhancing nitric oxide–mediated smooth muscle relaxation, increasing blood flow to the penis and facilitating erection.

Crossref | PubMed | Scopus (539) | Google ScholarSee all References Possible etiologies for ED secondary to hypertension include vascular damage due to hypertensive changes as well as hormonal abnormalities such as elevated prolactin levels.30x30Jaffe, A, Chen, Y, Kisch, ES, Fischel, B, Alon, M, and Stern, N. Erectile dysfunction in hypertensive subjects: assessment of potential determinants. Hypertension. 1996; 28: 859–862
Abstract | Full Text | Full Text PDF | PubMed | Scopus (272) | Google ScholarSee all References Between 1987 and 1989, the Massachusetts Male Aging Study (MMAS), a community-based random sample observational study of 1709 men, used self-administered sexual activity questionnaires to gather information about noninstitutionalized men aged 40 to 70 years in cities near Boston.4x4Feldman, HA, Goldstein, I, Hatzichristou, DG, Krane, RJ, and McKinlay, JB. Impotence and its medical and psychosocial correlates: results of the Massachusetts Male Aging Study. J Urol. 1994; 151: 54–61

When counseling diabetic men who are considering a PDE-5 inhibitor for ED, it is important to set realistic expectations and explain that studies document that all three agents are less effective in diabetic patients than in the general population of men with ED.45–49 For additional information, readers are referred to the excellent review of the use of PDE-5 inhibitors in diabetic men by Vickers and Satyanarayana.50
Older age. A man’s risk increases past the age of 40, as age is the variable most strongly associated with impotence. This is due to changing hormones, higher risk for heart problems and those affecting circulation, and decreased sexual desire that often occurs with increasing age. For example, based on findings from the National Health and Social Life Survey, it’s been found that “men between 50–60 years old are more than 3 times as likely to experience erection problems and to report low sexual desire compared to men aged 18 to 29 years.” (3)

PubMed | Google ScholarSee all References This prolonged excretion half-life produces enhanced erections up to 36 hours after oral dosing, thereby potentially allowing for more spontaneous engagement of intercourse. The efficacy of tadalafil in the treatment of ED has been proved in randomized double-blind, placebo-controlled trials.78x78Porst, H, Padma-Nathan, H, Giuliano, F, Anglin, G, Varanese, L, and Rosen, R. Efficacy of tadalafil for the treatment of erectile dysfunction at 24 and 36 hours after dosing: a randomized controlled trial. Urology. 2003; 62: 121–125
Yohimbe. Before Viagra and the other prescription erectile dysfunction drugs became available, doctors sometimes prescribed a derivative of the herb yohimbe (yohimbine hydrochloride) to their patients suffering from ED. But experts say the medication is not particularly effective, and it can cause jitteriness and other problems. "It's not a great drug," says McCullough. "And I suspect the herb is not as potent as the pharmaceutical version." What's more, evidence shows that yohimbe is associated with high blood pressure, anxiety, headache, and other health problems. Experts discourage its use.

Poor sleep patterns can be a contributing factor for erectile dysfunction, Mucher says. One review published in the journal Brain Research emphasized the intricate relationship between the level of sex hormones like testosterone, sexual function, and sleep, noting that testosterone levels increase with improved sleep, and lower levels are associated with sexual dysfunction. Hormone secretion is controlled by the body’s internal clock, and sleep patterns likely help the body determine when to release certain hormones. 

According to the Cleveland Clinic, “because erectile dysfunction is caused by a complex set of psychosocial, neurologic, and vascular factors, a specific cause in a patient may remain ambiguous.” The root causes are often related to a blockage or dysfunction of blood vessels. For example, ED can be due to conditions like atherosclerosis or diabetes, hormonal imbalances or problems related to mental health. It’s been found that common causes typically include one or more of the following factors: (2)
Abstract | Full Text PDF | PubMed | Scopus (3562) | Google ScholarSee all References By 1996, fueled by the availability of the new oral agent sildenafil, the number of outpatient visits for ED as estimated by the National Ambulatory Medical Care Survey had increased to 1.3 million per year.5x5Feldman, HA, Johannes, CB, Derby, CA et al. Erectile dysfunction and coronary risk factors: prospective results from the Massachusetts Male Aging Study. Prev Med. 2000; 30: 328–338
The same device is considered a vacuum erectile device (VED), when it is used to increase inflow of the blood to the penis without a constriction band. Regular use of VED in post-prostatectomy patient increases penile oxygenation and is accepted as a valid option in penile rehabilitation. Recent study reported transient increase in oxygenation to the glans penis and corporal bodies were detected by oximetry after VED was applied, providing proof for possible role for VED to counter the early penile hypoxia, cavernosal fibrosis and long-term ED after radical prostatectomy (9).
According to Harvard Special Health Report Erectile Dysfunction, one study in the European Heart Journal looked at men newly diagnosed with heart disease, but without ED, who started treatment with the beta-blocker atenolol (Tenormin). Some of the study participants were told about the sexual side effect of the blood pressure drug, and ED was reported by almost one-third of the participants. In contrast, among those who were not told the drug's name or its side effects, only 3% said they experienced ED.
There have been some studies to suggest that a placebo effect that improves ED may work for some men. One study found that men taking an oral placebo pill showed as much improvement in ED symptoms as men who took actual medication to improve ED. Conversely, men who were given therapeutic suggestions to improve ED did not see signs of symptom improvement.
Normal male sexual function requires a complex interaction of vascular, neurological, hormonal, and psychological systems. The initial obligatory event is acquisition and maintenance of an erect penis, which is a vascular phenomenon. Normal erections require blood flow into the corpora cavernosae and corpus spongiosum. As the blood accelerates, the pressure within the intracavernosal space increases dramatically to choke off penile venous outflow. This combination of increased intracavernosal blood flow and reduced venous outflow allows a man to acquire and maintain a firm erection.
Crossref | PubMed | Scopus (35) | Google ScholarSee all References Also, if lower blood pressure level was the primary etiology of ED, all classes of antihypertensive agents should be expected to have relatively similar effects on erectile function because of their efficacy in lowering pressure, which has not been seen.6x6Kloner, RA. Erectile dysfunction and cardiovascular risk factors. Hosp Pract (Off Ed). 2001; 36: 41–44 (49-51.)
Crossref | PubMed | Scopus (23) | Google ScholarSee all References Similar to sildenafil, vardenafil produces a slight hypotensive effect with an average maximal decrease in blood pressure level of 5 to 10 mm Hg.74x74Gresser, U and Gleiter, CH. Erectile dysfunction: comparison of efficacy and side effects of the PDE-5 inhibitors sildenafil, vardenafil and tadalafil—review of the literature. Eur J Med Res. 2002; 7: 435–446

PubMed | Google ScholarSee all References As with sildenafil, use of nitrate or NO-donor medications is contraindicated while taking tadalafil because of the potential for marked hypotensive interactions.74x74Gresser, U and Gleiter, CH. Erectile dysfunction: comparison of efficacy and side effects of the PDE-5 inhibitors sildenafil, vardenafil and tadalafil—review of the literature. Eur J Med Res. 2002; 7: 435–446

Most of the time, ED is the first symptom of poor cardiovascular health. Hypertension oftentimes doesn’t manifest outward symptoms of heart disease.  Some men go undiagnosed with high blood pressure for a long time. It can be troublesome for many men who feel uncomfortable discussing ED with their health providers. Many fail to seek medical advice and suffer from progressive worsening of their cardiovascular problems before deciding to undergo treatment.
In the early years of my cardiology practice, I was surprised by the number of men with heart disease who also suffered from impotence. In fact, being incapable of having an erection was the norm rather than the exception after heart attack. In those days, impotence was widely attributed to the psychological depression that often followed heart attack.
There are a number of reasons a man may not achieve the desired result from an oral erectile dysfunction drug. In some cases, a man may experience drug side effects severe enough to outweigh any potential benefit of taking the drug. Possible side effects of these drugs include headache, facial flushing, nasal congestion, and transient abnormal vision. (In October 2007, the FDA added a warning about sudden hearing loss to the package labels of oral erectile dysfunction drugs. While it’s not absolutely clear that the drugs can cause sudden hearing loss, a number of cases have been reported in men within hours or days of taking one of the drugs.)
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