Erectile Dysfunction or Impotence

What is impotence?

Impotence is a consistent inability to sustain an erection sufficient for sexual intercourse. Medical professionals often use the term "erectile dysfunction" to describe this disorder and to differentiate it from other problems that interfere with sexual intercourse, such as lack of sexual desire and problems with ejaculation and orgasm. This FAQ focuses on impotence defined as erectile dysfunction.

Impotence can be a total inability to achieve erection, an inconsistent ability to do so or a tendency to sustain only brief erections. These variations make defining impotence and estimating its incidence difficult. Experts believe impotence affects between 10 and 15 million American men.

How does an erection occur?

The penis contains two chambers, called the corpora cavernosa, which run the length of the organ.

A spongy tissue fills the chambers of the corpora cavernosa. The corpora cavernosa are surrounded by a membrane, called the tunica albuginea. The spongy tissue contains smooth muscles, fibrous tissues, spaces, veins, and arteries. The urethra, which is the channel for urine and ejaculate, runs along the underside of the corpora cavernosa.

Erection begins with sensory and mental stimulation. Impulses from the brain and local nerves cause the muscles of the penile arteries and the muscles of the spongy corpora cavernosa to relax, allowing blood to flow in and fill the open spaces in the spongy tissue. The blood creates pressure in the corpora cavernosa, making the penis expand. The tunica albuginea helps to trap the blood in the corpora cavernosa, thereby sustaining erection. The erection could be compared to the action of air in a bicycle tire. Air is forced into the inner tube under pressure. The inner tube (corpora cavernosa) presses against the outer tube (tunica albuginea) creating firmness. The blood is trapped in the corpora cavernosa sustaining the erection, similar to the air trapped in the tire's inner tube.

Erection is reversed when muscles in the penis contract, stopping the inflow of blood and opening outflow channels and allowing the blood to return to the body's circulatory system.

What causes impotence?

Impotence usually has a physical cause, such as disease, injury or drug side effects. Any disorder that impairs blood flow in the penis has the potential to cause impotence. Incidence rises with age. About 5 percent of men at the age of 40 and between 15 and 25 percent of men at the age of 65 experience impotence. It is not, however, an inevitable part of aging.

Since an erection requires a sequence of events, impotence can occur when any of the events is disrupted. The sequence includes nerve impulses in the brain, spinal column and area of the penis, and response in muscles, fibrous tissues, veins, and arteries in and near the corpora cavernosa.

Damage to arteries, smooth muscles, and fibrous tissues, -- often as a result of disease -- is the most common cause of impotence. Diseases -- including diabetes, kidney disease, chronic alcoholism, multiple sclerosis, atherosclerosis, and vascular disease - account for about 70 percent of cases of impotence. Between 35 and 50 percent of men with diabetes experience impotence.

Surgery (prostate surgery, for example) can injure nerves and arteries near the penis, causing impotence. Injury to the penis, spinal cord, prostate, bladder and pelvis can lead to impotence by harming nerves, smooth muscles, arteries and fibrous tissues of the corpora cavernosa.

Also, many common medicines produce impotence as a side effect. These include high blood pressure drugs, antihistamines, antidepressants, tranquilizers, appetite suppressants and cimetidine (an ulcer drug).

Experts believe that psychological factors cause 10 to 20 percent of cases of impotence. These factors include stress, anxiety, guilt, depression, low self-esteem and fear of sexual failure. Such factors are broadly associated with more than 80 percent of cases of impotence, usually as secondary reactions to underlying physical causes.

Other possible causes of impotence are smoking, which affects blood flow in veins and arteries, and hormonal abnormalities, such as insufficient testosterone.

How is impotence diagnosed?

Patient history

Medical and sexual histories help define the degree and nature of impotence. A medical history can disclose diseases that lead to impotence. A simple recounting of sexual activity might distinguish problems with erection, ejaculation, orgasm or sexual desire.

A history of using certain drugs can suggest a chemical cause. Drug effects account for 25 percent of cases of impotence. Cutting back on or substituting certain medications often can alleviate the problem.

Physical examination

A physical examination can give clues for systemic problems. Careful attention must be paid to the circulatory and neurological systems (blood vessels and nerves) and, of course, the genitals (penis and testicles). Unusual characteristics of the penis itself could suggest the root of the impotence -- for example, bending of the penis during erection could be the result of Peyronie's disease.

Laboratory tests

Several laboratory tests can help diagnose impotence. For cases of low sexual desire, measurement of testosterone in the blood and other hormones made in the brain that control the levels of testosterone can yield information about problems with the endocrine system. These may include luetenizing hormone (LH), follicle stimulating hormone (FSH) and prolactin. Tests for systemic diseases may include thyroid hormone levels, blood counts, urinalysis, lipid profile, and measurements of kidney and liver function.

Other tests

Monitoring erections that occur during sleep (nocturnal penile tumescence) can help rule out certain psychological causes of impotence. Healthy men have involuntary erections during sleep. If nocturnal erections do not occur, then the cause of impotence is likely to be physical rather than psychological.

Psychosocial examination

In some cases, a psychosocial examination, using an interview and questionnaire, reveals psychological factors. The man's sexual partner may also be interviewed to determine expectations and perceptions encountered during sexual intercourse. These interviews may be performed by a sex therapist, psychologist, psychiatrist, or any health provider with an interest in the psychological aspects of sexual problems.

What are the medical treatments for impotence?

When a psychological problem is discovered, counseling can help by working with couples and reducing tension, improving communications, and trying to obtain realistic expectations. In some patients where psychologic causes are not the originating problem but have become a significant factor, counseling may be necessary during the difficult rehabilitation period.

Lifestyle modifications may be beneficial, including changes in exercise, stress levels, diet, alcohol, smoking and illicit drug use, if these are considered major contributing factors.


The newest and most exciting development is in pill form. The drug called sildenafil (or Viagra) has been studied in England and seems to improve erections in men who have no known cause for difficulty with erections. Studies on men with known causes, such as surgery or diabetes, have not been completed, but early data are promising. Viagra works by increasing blood flow to the penis. The drug is available now. Early studies show very few side effects. The drug does not directly cause erections, but enhances erections caused by sexual stimulation. It works by partially blocking an enzyme in the penis that is responsible for normally reversing erections. Some studies have shown 60 to 80 percent effectiveness in selected patients who had difficulty maintaining erections. About one in 25 men discontinued therapy because of side effects, which included headache, indigestion, visual disturbances and flushing. Viagra comes in four different dosages, and onset of action begins within 20 to 60 minutes. The effect lasts for four hours. Only one dose per day is recommended. Diabetics and men who have had radical prostate or bladder surgery have a lower success rate with Viagra.

Important note: Patients who take or need nitroglycerin or nitrates for heart disease cannot use this drug. A number of heart attacks, some causing death, have been reported since the introduction of Viagra. These appear to be due to the exertion of sexual intercourse or to the use of nitroglycerin with Viagra against doctor's orders. Patients with significant heart disease, whether using nitroglycrin or not, should be counseled about the risk of heart attack.

Hormone therapy

Hormone treatments, namely testosterone, can be used in men whose production of male hormones is low. Testosterone injections generally only help men who have low levels of testosterone, which can be measured by the physician at the initial evaluation. Testosterone injections are not without problems, however, as the use of the drug can stimulate the growth of prostate tissue. Testosterone cannot be used in patients with known or suspected prostate cancer, as the cancer could grow more rapidly. Other less common side effects of testosterone use include liver injury and increased blood pressure. Men who regularly take testosterone usually stop sperm production, and permanent infertility could result if testosterone is used long enough.


Yohimbine is a medication made from the bark of a tree that grows in India and Africa. Yohimbine acts on the nervous system and may also have some effect on increasing the male libido. It is considered homeopathic by medical doctors; that is, no definite uses are proven. The drug is very safe with uncommon side effects (such as mild dizziness, nervousness, irritability, headaches and nausea) rarely occurring. Some studies have suggested 10 to 20 percent of men will respond to the treatment with yohimbine, but it is necessary to take the medicine for a full two months before knowing whether or not it is going to work. Nevertheless, a task force of specialists sponsored by the American Urological Association has recently determined that yohimbine is no more effective than a placebo.


Trazodone is an antidepressant drug that was found to induce prolonged erections in some men. This side effect was unwanted and the prolonged erections caused problems in many patients, butin lower dosages (usually 100 mg at bedtime) it can promote normal erections. Trazodone can cause drowsiness, nausea and difficulty urinating.

Self-injection therapy

What is self-injection therapy? This involves the patient or his partner giving an injection of medication directly into the side of the penis to create an erection. The erection created is a natural one and usually begins five to 15 minutes after the injection. Not all patients respond to this type of treatment, but those who do should develop an erection that lasts anywhere from 30 to 120 minutes. About 70 percent of men find that their erections are satisfactory with self-injection therapy. The injections are given with a tiny needle and use very small amounts of medicine. The injections are relatively painless and are easily taught to the patient in one or two visits with the doctor.

The drugs used today include prostaglandin (PGE-1 or Prostin or Alpoprostadil or Caverject), Papaverine hydrochloride and phentolamine (Regitine). All of these drugs have been approved by the FDA for uses other than impotence treatment. Only prostaglandin has been approved by the FDA for treating impotence. Papaverine and phentolamine have not yet been approved by the FDA for this specific purpose, although these two drugs were the initial ones used for self-injection therapy. Nevertheless, considerable experience has been obtained by urologists over the past decade and the all three drugs mentioned above are considered safe for self-injection therapy.

As mentioned, these medications have not been approved by the FDA and so technically need to be considered experimental. All medications have some potential risks and side effects, and risks do exist with all these drugs and the injections. These may include the possibility of bleeding or bruising from the injection, and the small chance of infection. One of the more common risks includes the development of a prolonged erection, or priapism (more than four hours). An episode of priapism might require a trip back to the physician or to the emergency room to receive other medications to counteract the self-injection medications and relieve the prolonged erection. Priapism happens in only a few percent of the patients. The patient does need to be aware, however, that any erection lasting more than four hours needs to be dealt with by a physician. Another complication is the development of permanent scarring within the penis. The medications can be irritating to the penile tissues, and scarring is most often seen in patients who abuse the drug by using it too often. Scarring could create difficulty obtaining erections even with additional medication. If the scarring were severe, placement of a penile prosthesis (if that option was chosen at a later time) might be difficult. Even rarer is the development of other medical problems. Papaverine has been known to cause changes in liver function tests, which go away if the drug is stopped. Some men complain of dizziness, heart palpitations and/or a flushed feeling with these medications.

Self-injection treatment does require that the patient or his partner learn to give injections directly into the penis. The patient needs to return to the doctor for follow-up visits, particularly in the early phases of treatment. The patient cannot use the injections too often or he may develop scarring, and the self-injection treatment should be limited to once every four to seven days. (Range depends on medication type and initial response.)

The injections are relatively costly, depending on what combinations of medications are used. An injection may cost up to $8 to $10 per injection.

Not all patients are candidates for self-injection therapy. A percentage of patients will not develop good erections, while others might develop erections that do not go away, making them poor candidates for continued use of this drug.

The major advantage of self-injection therapy is that the erection created is similar to the body's own spontaneous erections. The erection lasts usually 30 to 120 minutes, which is adequate duration for successful and pleasing intercourse. Self-injection therapy does not impede the development of an orgasm or ejaculation. Self-injection therapy is less costly than surgical implantation. Self-injection therapy can be used by the patient at his own discretion and at any time with a minimum of preparation. Treatment does not involve surgery and is minimally painful in most patients.

If you decide to start the self-injection program, you will return to the office for test doses to see which drug and dosage is most appropriate and effective for you. After we have established the drug dose, we will then teach you how to draw medication from a vial, and also how to inject it safely into the penis. You may want your partner to learn the procedure, although a partner is not absolutely necessary if you have good dexterity and eyesight. We will have you read, understand and sign a consent form. The form will mention the various risks of the medications and injections. We will go over all these risks and conditions in detail at the time of the educational program. If you have any questions about self-injection therapy, please don't hesitate to ask us.


MUSE is the name of a new drug treatment and represents a unique approach to the treatment of erectile dysfunction. It is based on the discovery that the urethra (the tube in the penis for urine to pass from the bladder to the outside of the body) can absorb certain medications into the surrounding erectile tissues, thereby creating an erection. The MUSE system uses prostaglandin E1, the same medication used in the self-injection therapy, and has been approved by the FDA for the treatment of impotence.

An erection should begin within five to 10 minutes after administering MUSE. The duration of effect is approximately 30 to 60 minutes, but the actual duration will vary from patient to patient.

The most common side effects reported after using MUSE are aching in the penis, testicles, legs and in the area between the scrotum and the rectum; warmth or burning sensation in the urethra; redness of the penis due to increased blood flow; and minor urethral bleeding or spotting due to improper administration.

MUSE was released in early 1997 and more experience will be gained in these first few years that it is available to the public through their physicians. It is likely that MUSE will not be as effective as the self-injection therapy because of the variability of absorption of the medication, and it will most definitely be more expensive. The absence of needles, however, makes this form of therapy very attractive for those men in whom the treatment works.

Vacuum device The vacuum erection device is a simple mechanical tool that allows the man to develop an erection suitable for sexual intercourse.

Erections are created when blood is trapped in the penis, much like air is trapped in an inflated tire. The more air that is placed into the tire, the firmer the tire becomes. Likewise, the more blood trapped temporarily in the penis, the firmer the erection. The vacuum erection device works by bringing more blood into the penis and then trapping it. The penis is inserted into a hollow plastic tube, which is pressed against the body creating a seal. A vacuum is then created in the tube by use of a small hand pump. This in turn draws blood into the penis, causing engorgement, enlargement and rigidity. After one to three minutes of vacuum, an adequate erection is created and a soft rubber O-ring is then placed around the base of the penis in order to trap the blood and maintain the erection. The vacuum tube is removed and sexual intercourse is then possible. The rubber O-ring will maintain the erection until removed, and in most circumstances this can be left in place for 25 to 30 minutes.

A vacuum erection device works best in patients who are able to achieve a partial erection on their own. After having adequate foreplay, which creates a mild erection, the partner can help in applying and using the vacuum device. In any type of sex therapy, the partner's full acceptance of whatever technique is used is always helpful.

Safety is one of the major advantages of a vacuum erection device. There is no surgery, internal injections or significant side effects. The vacuum erection device will work for almost any type of erectile problem. The cost of the vacuum erection device is less than surgery or the continued use of self-injection treatments. The vacuum device can be used at the patient's convenience and at any time. Most of the major companies that manufacture vacuum erection devices provide a refund policy if the vacuum erection device is not successful. The vacuum erection device ranges in cost from $300 to $500 and requires a prescription. Some insurance companies will reimburse all or part of the costs.

One of the disadvantages of the vacuum erection device is the mechanical aspect of obtaining an adequate erection. This might have a negative influence on the patient and his partner. The device takes five to 10 minutes to set up, which technically interferes with foreplay. Some patient's body build makes it difficult to apply the vacuum erection device. Once the rubber O-ring is applied, there is no erection between the rubber band and the body, making the penis somewhat floppy.

The O-ring inhibits the normal flow or ejaculation after orgasm in some patients, although this is not harmful and the semen will pass once the rubber band is removed. Some patients complain of a sense of coldness and/or numbness of the penis after the O-ring has been placed. The O-ring should be removed after 25 to 30 minutes because of restricted blood flow. The erection will soften when the O-ring is removed. A vacuum erection device might be harmful to patients who have blood clotting problems or who use blood thinners because of bleeding into the tissue.

If you have any questions about the vacuum erection device, please don't hesitate to ask us. We have videotapes available for further information, and you need only borrow a tape or come into the office to view it.

Penile prosthesis

Implantation of a penile prosthesis is one of several options available for the treatment of impotence. The penis consists of three hollow tubes running along the length of the shaft. One of these, the urethra, runs along the bottom of the penis and brings urine from the bladder out through the end of the penis. The other two matched tubes running side-by-side on the top of the penis are constructed much like an automobile tire with an outer tube and an inner tube. The erection is created by the two inner tubes filling and pushing against the outer tubes, much like a tire that is inflated with air.

One of the treatment options for erectile dysfunction is the placement of prosthetic inner tubes within the penis to mimic the inflation process and create an erection. Penile implants were first used in the 1950s, and since then further advances have occurred. Different types of prostheses have been developed, and hundreds of thousands of men throughout the world have been successfully treated with penile implants.

Today there are three types of penile prostheses: the semi-rigid implant, the inflatable implant and a self-contained inflatable implant.

Semi-rigid implants are paired, silicone-covered, malleable (bendable) metal rods. The semi-rigid prosthesis allows the penis to be rigid enough for penetration, but the malleable rods allow it to be flexible enough to allow concealment in a curved position. It is the simplest of all prostheses and has the least chance of mechanical failure. It is also the simplest to place.

One major limitation is that the penis is always semi-erect. Even thought it can bend, concealment is a potential problem when wearing some types of clothing. Another disadvantage is that the prosthesis does not inflate, so the erection achieved is only from the size and rigidity of the prosthesis.

Inflatable prostheses are the most natural of the implants. These are soft, paired inner tubes made of silicone or bioflex, which are inert plastics. The inner tubes are filled with a solution that comes from a small reservoir placed under the muscles of the abdomen. A pump is used to transfer the fluid from the reservoir to the penile cylinders (inner tubes). The more fluid that is pumped into the inner tubes, the firmer and larger the erection. When the erection is no longer desired, the fluid returns to the reservoir, leaving the penis soft and pliable.

A major advantage of an inflatable penile implant is a more natural erection with total patient control, both in the amount of fluid that is put into the penis and the time the erection is desired. The erection will last indefinitely until the patient transfers the fluid back into the reservoir. One major disadvantage is that the surgical implantation is a little more complicated than a simple semi-rigid implant. Also, with the multiple parts there is a higher chance of mechanical failure which might require revision or repair. Many of the companies do have insurance policies to cover part or all of the costs of the prosthesis replacement but not the surgical or hospital fees.

Self-contained inflatable implants are paired silicone cylinders which have a pump at the very tip of the prosthesis, along with a reservoir within the shaft that transfers fluid in such a way that the cylinder becomes firm.

The advantage of this type of prosthesis is that the surgery is somewhat simpler than the multicomponent prosthesis.

The major disadvantage is that the inflatable portion of it does not significantly increase the girth of the penis. It is also not as soft or as easily concealed as the multicomponent implant when deflated.

Implants are effective in treating almost every cause of impotence. There is over a 90 percent success rate when both partners are informed of the nature and limitations of the prosthesis. Prostheses require no further treatment after implantation, and there is no external equipment which might have negative connotations to the partner. No medicines or injections are needed, and once the prosthesis is placed and functioning there are no further costs. The newer prostheses are very reliable and the chance of mechanical failure is very low, in the range of 2 to 4 percent per year.

Once an implant has been placed, natural erections usually no longer occur. If the prostheses were later removed, the normal erections would be unlikely to return. There is a small chance of infection, which would require removal of the prosthesis. Some patients can develop surgical complications or anesthetic complications. Occasionally, a patient will notice numbness at the head of his penis, and intercourse can be uncomfortable. Because the erection is not caused by increased blood flow to the penis, the head of the penis is not part of the erection, and this softness may be bothersome to some patients.

Recently, the safety of silicone and silicone products such as silastic have been questioned. Breast prostheses using liquid or gel forms of silicone were removed from the market by the FDA. Concerns raised were the inflammatory responses to this type of silicone, which included pain, scarring and disfigurement. In addition, possible associations were raised between silicone and the development of immune disorders, such as rheumatoid arthritis, and a possible association to an increased development of cancer. It is noteworthy that the solid silicone breast implants that are filled with water were not removed from usage. In May 1994 a class action suit was filed against the major manufacturer of penile prostheses, claiming many of these same issues. The penile prostheses are all of the solid variety and use water as a filling. Most observers feel the suit is without basis, but of course, only time will tell, and there needs to be more research and follow-up. Solid silicone products are used extensively in medicine and include cardiac pacemakers and brain shunts. Thousands and thousands of implants of all types have been used for years with very few and predictable risks and side effects.

Some insurance policies will cover the cost of prostheses; this can be established through our business office. Patients who are considering a prosthesis should be aware that other types of therapy might be available, including vacuum devices and self-injection therapy.

Vascular reconstructive surgery

A small percentage of patients may be candidates for some form of reconstruction of the penile blood flow. These include patients with poor arterial blood supply and those with venous leaking. The long-term results from this type of surgery have been generally disappointing -- even the best results show only 1 out of 20 men were helped. Surgery is technically difficult, relatively expensive, and includes complications of nerve damage and scar tissue formation. Given the relatively low success rate, technical difficulty and expense of this type of procedure, vascular reconstructive surgery has not been generally or widely accepted.

Sex therapy

For many years physicians believed almost all sexual dysfunction was caused by psychologic reasons. As we reached a better understanding of the physiology of erections, it became known that many problems with impotence are, in fact, caused by physiologic reasons that the patient cannot control. A significant number of men, however, still develop erectile problems purely on the basis of psychologic causes. In addition, men with an underlying physical disorder often develop psychologic problems because of their lack of performance. Even if the physiologic (or as physicians often say, "organic") problem is corrected, the man's self-image and confidence may be affected significantly enough that return to normal functioning is difficult.

Psychologic problems are often difficult to discuss with -- or even mention to -- a physician. Once the lack of confidence is deeply imbedded in the man's psyche, the subsequent lack of confidence becomes very difficult to remove from the man's thinking. He may also feel deep frustration, anger, depression and a sense of inadequacy.

Whether the difficulty in maintaining or achieving erections is purely psychologic or secondary to another physiologic cause, the end result creates a lack of confidence which results in a "self-fulfilling prophecy." The patient is so fearful of not obtaining an erection that the worry becomes overwhelming and fears are born out -- no erection or a loss of erection.

Sex therapists are trained professionals who deal uniquely with sex problems. They may provide reading material and videos, and are very goal-oriented in providing techniques, advice and counseling on the sexual problem.. Usually, only a few visits will provide definite improvement, and no more than a few months of treatments are generally required before one sees definite results. Recognizing additional causes of stress, obtaining adequate expectations from your partner and looking at relationships are also essential to effective sexual counseling. Some of the more specific treatments include exercises or treatment plans that are carried out in the privacy of one's home and which do not require in-hospital or in-office treatments. The patient's partner is definitely brought into the technique training. By working together to reduce anxiety and increase confidence, partners can help each other relieve some of the anxiety and reestablish a normal sexual relationship.

Sex therapy is also helpful in patients who have premature ejaculation or difficulty in obtaining an ejaculation.

In some patients the problems are so deep-seated that the pure psychologic techniques are not effective. In these cases the sex therapist might work in concert with the physician, using a technique such as a vacuum erection device or self-injection therapy to aid in the early achievement of erections. As the patient's self-confidence improves, these therapies might be discarded, although they can be used into the future as well. On occasion, medications or injections of hormones can be used to help initiate or stimulate early sexual functioning. Sex therapy is usually not covered by insurance policies, but it is unlikely that the counseling will need to continue past six months or so, which should keep the costs within most people's budgets.

External supports

Some men have had success using external support devices, the most popular of which is called Rejoyn. These devices are essentially a semi-rigid condom. They are placed over the penis and provide the necessary rigidity without the need of an erection. These can be purchased without a prescription at many pharmacies or by calling 1-800-297-9329 for more information.

What does not work?

At this point there is no evidence that nutritional supplements or vitamins have any significant bearing on sexual performance. The Food and Drug Administration has currently banned the sale or advertising of all nonprescription products for the treatment of male impotence because none has been scientifically shown to be effective. Nitroglycerin patches and minoxidil (the drug for baldness) have not been shown to be effective for impotence when used as penile patches.

What's new?

Another new oral (taken by mouth) drug is apomorphine. This drug also seems to promote erections in men with psychogenic problems Apomorphine may also work in men having difficulty maintaining erections. Large studies are currently underway in the US to determine the safety and effectiveness of these drugs. Yet another oral drug is Vasomax (phentolamine). This medicine is still being tested and does not seem to have the effectiveness of Viagra, with a 40 percent response in men tested. At higher doses, a lowering of blood pressure may be problematic.

All of the oral drugs have different modes of action and if one does not work, the others may. Combinations of drugs (e.g., Viagra and another drug) and other techniques may also be possible.

In recent European studies, a new injectable drug called VIP was tested. VIP stands for vasoactive intestinal peptide. When mixed with phentolomine (Regitine), which is an older injectable drug, 80 percent of men had successful erections, even if they had failed other injectables. Studies are just beginning in the US.

Two other injectables being researched abroad are moxislyte and forskolin. Initial success rates of 80 percent are being reported. No US studies are yet completed.

North American studies of creams containing nitroglycerin that are applied to the penis have shown modest success in mild-to-moderate erectile dysfunction. There are plans to study this drug in the US. South American studies of creams containing prostaglandin (Alprox-TD) that are applied to the penis have shown modest success in mild-to-moderate erectile dysfunction. There are no plans to study this drug in the US at this time.