Sildenafil is available as oral tablets at doses of 25 mg, 50 mg, and 100 mg. Patients should take sildenafil approximately one hour before sexual activity. In some men, the onset of action of the drug may be as early as 11-20 minutes. It's best for men to take sildenafil on an empty stomach for best results since absorption and effectiveness of sildenafil can be diminished if it is taken shortly after a meal, particularly a meal that is high in fat. Sildenafil and the other PDE5 inhibitors don't cause an immediate erection. Sexual stimulation is necessary for these medications to work.
One report from a recent community survey concluded that erectile failure was the leading complaint of males attending sex therapy clinics. Other studies have shown that erectile disorders are the primary concern of sex therapy patients in treatment. This is consistent with the view that erectile dysfunction may be associated with depression, loss of self-esteem, poor self-image, increased anxiety or tension with one's sexual partner, and/or fear and anxiety associated with contracting sexually transmitted diseases, including AIDS.
If PDE5 drugs don't work or cannot be used because of potential side effects, your doctor can recommend other therapies. The drug alprostadil (Caverject, Edex, Muse) allows blood to flow more freely in the penis, leading to an erection. The drug can be injected with a tiny needle into your penis. Or, a small pellet (suppository) can be inserted into the opening of the penis. Suppositories and injections are effective in the majority of men.
The association of CVD and ED was noted in 1997 as one analysed the results of the MMAS. In this landmark study, 1709 men aged 40–70 years were enrolled between 1987 and 1989. A follow-up some 10 years later revealed a striking relationship between ED and CVD. In this study, it became clear that the risk factors for ED were very similar to those of CVD, such as diabetes mellitus, smoking and dyslipidaemia.18
Alprostadil should not be used in men with urethral stricture (scarring and narrowing of the tube that urine and the ejaculate pass through), balanitis (inflammation/infection of the glans [tip] of the penis, severe hypospadias (a condition where the opening of the urethra is not at the tip of the penis, rather on the underside of the penis), penile curvature (abnormal bend to the penis), and urethritis (inflammation/infection of the urethra).
Associated morbidity may include various other male sexual dysfunctions, such as premature (early) ejaculation and male hypoactive sexual desire disorder. The NHSLS found that 28.5% of men aged 18-59 years reported premature ejaculation, and 15.8% lacked sexual interest during the past year. An additional 17% reported anxiety about sexual performance, and 8.1% had a lack of pleasure in sex. 
The Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) study, designed to determine whether an individual man’s sexual outcomes after most common treatments for early-stage prostate cancer could be accurately predicted on the basis of baseline characteristics and treatment plans, found that 2 years after treatment, 177 (35%) of 511 men who underwent prostatectomy reported the ability to attain functional erections suitable for intercourse. 
Penile prostheses are very effective, and most patients who have a prosthesis placed are satisfied with the prosthesis. However, placement of a prosthesis causes scarring of the tissue within the corpora cavernosa, and if the prosthesis requires removal, other forms of therapy, except for the vacuum device, are often not effective. Thus, most physicians reserve placement of a prosthesis for men who have tried and failed or have contraindications to other therapies.
Because of the difficulty in defining the clinical entity of erectile dysfunction, there have been a variety of entry criteria for patients in therapeutic trials. Similarly, the ability to assess efficacy of therapeutic interventions is impaired by the lack of clear and quantifiable criteria of erectile dysfunction. General considerations for treatment follow:
Men with physical causes of ED have options, including such medicines as sildenafil (Viagra®), vardenafil (Levitra®), or tadalafil (Cialis®). Men who use nitroglycerin products and those who should avoid sexual activity because of cardiovascular disease shouldn’t take these drugs. Other treatment modalities include use of a vacuum pump or injection of a substance (papaverine) into the penis to increase blood flow to the penis. Men can also have surgery to put a prosthesis into the penis.
The nerves and endothelium of sinusoids and vessels in the penis produce and release transmitters and modulators that control the contractile state of corporal smooth muscles. Although the membrane receptors play an important role, downstream signaling pathways are also important. The RhoA–Rho kinase pathway is involved in the regulation of cavernosal smooth muscle contraction. 
It is important that physicians and other health care providers treating patients for chronic conditions periodically inquire into the sexual functioning of their patients and be prepared to offer counsel for those who experience erectile difficulties. Lack of sexual knowledge and anxiety about sexual performance are common contributing factors to erectile dysfunction. Education and reassurance may be helpful in preventing the cascade into serious erectile failure in individuals who experience minor erectile difficulty due to medications or common changes in erectile functioning associated with chronic illnesses or with aging.
Sexual dysfunction and ED become more common as men age. The percentage of complete ED increases from 5% to 15% as age increases from 40 to 70 years. But this does not mean growing older is the end of your sex life. ED can be treated at any age. Also, ED may be more common in Hispanic men and in those with a history of diabetes, obesity, smoking, and hypertension. Research shows that African-American men sought medical care for ED twice the rate of other racial groups.