Erectile dysfunction: How effective are drugs for treating impotence such as Viagra, and what are their adverse effects?

The long-term use of sildenafil (Viagra), vardenafil (Levitra) and tadalafil (Cialis) in erectile dysfunction has not been well studied. The drugs can increase the likelihood of satisfying sex, but about 2 out of every 10 users will experience adverse effects.

Erectile dysfunction (ED) is the medical term for what is often called impotence. Doctors define ED as the inability of a man to get or keep an erection that is firm enough for satisfying sexual intercourse when he is aroused. It has many different causes and may happen because of a temporary situation, like too much alcohol or stress. However for many men ED happens frequently because it is caused by a chronic illness like diabetes. ED can also be an adverse effect of medications and of treatments for prostate problems or prostate cancer.

If a man seeks medical help for ED, the first issue for the doctor is to accurately diagnose if there is any illness or medication that is causing the problem. In fact, this could be the first noticeable symptom of a problem like high blood pressure (hypertension). Treating the underlying health problem might not only be important for the man’s overall health, but it might also help improve erections. Many men are reluctant to discuss ED, so they may not realize how common it is. Some estimates suggest that once men are over 40 years old, it could affect every second man.

Drug and non-drug options for improving erections

Depending on the cause of ED and the preferences of the man (and often his partner), there are several options to try. If the problem might be caused by stress, or the ED is causing a lot of psychological stress, then counseling or other similar therapy from a doctor, psychologist or sex therapist might be suitable. Regardless of what form treatment takes, both partners in a relationship may find it a great relief to speak openly about erection problems.

Some men also decide to use treatments like penis pumps or implants, or to try hormone therapy, including testosterone. In recent years, though, Viagra and similar drugs have become popular options for helping to improve erections.

Sildenafil (trade name Viagra) was the first of a group of drugs called PDE-5 inhibitors. These were originally intended to be used for heart disease, and the effect on erections was a side effect of drug use.

Erections become firm because of enough blood filling up spongy tissue in the penis. For this to happen, the blood vessels that run through these parts have to expand, which is only possible when the blood vessel muscles relax.

PDE-5 (short for phosphodiesterase-5) inhibitors work by slowing an enzyme found in the spongy tissues of the penis. Phosphodiesterase 5 (PDE 5) is responsible for breaking down a messenger substance produced by the body that controls the relaxation of the blood vessel muscles. PDE-5 inhibitors make this messenger substance last longer so that enough blood can flow into the spongy tissue of the penis, improving the erection. The drug is not taken regularly, but only a few hours before a man wants to have an erection. Because the drug can also sometimes cause heart problems or interact with particular other medications, it is not recommended for some men. This particularly includes those who take nitrate drugs for heart disease because there have been individual reports of severe complications as a result of that specific combination.

Trial data only on short-term use of PDE-5 inhibitors

Researchers working under commission from the American College of Physicians and the American Agency for Health Care Research and Quality (AHRQ) looked for randomized controlled trials testing PDE-5 inhibitors. In some of these trials, men with ED volunteered to take either a PDE-5 inhibitor or placebo (dummy tablet) after researchers assigned them by chance to one of these groups. In other trials the PDE-5 inhibitors were compared with one another, and not with a placebo. The men participating in these trials did not know which tablet they were using. This means that the researchers could be fairly sure that any differences in erections were being caused by the drug’s ingredients, and not because of a psychological effect or because there were differences between the two groups. You can read more about why drugs and other treatments need to be tested this way here.

The researchers found 130 trials of PDE-5 inhibitors – nearly half of them for sildenafil (Viagra), with vardenafil (Levitra) and tadalafil (Cialis) also being studied in many trials. Unfortunately, though, few of the trials lasted for longer than three months, and adverse effects were not routinely studied. So many questions about these drugs remain unanswered. There were only 4 trials that compared these drugs with each other. This did not show any important differences between the drugs, but more and better research is needed before we can be certain that the drugs are much the same.

The researchers also found some signs that the drugs’ manufacturers might not have published all the trials they had done. As this may mean that trials with more disappointing results were not available to the researchers, they caution that the available research results might exaggerate the benefits of the drugs a little. There is no doubt, though, that the drugs can improve erections for many men.

Improved erections, but with common adverse effects

The researchers concluded that the three main PDE-5 inhibitors can double the chance of satisfying sexual intercourse – the rate of intercourse judged as “successful” in the trials was about 35% in men taking placebos, and around 69% in men using sildenafil (the PDE-5 inhibitor that was best studied). The proportion of men taking PDE-5 inhibitors who had improved erections ranged between 73% and 88% (compared with a range between 26% and 32% in the group of men taking placebos).

These short-term trials could not produce conclusive scientific evidence on serious adverse effects such as heart attacks. There were some serious heart problems in the group of men taking the drugs, but more research is needed to be certain about this risk. The most reliable data are available for sildenafil, because that is the drug that has been most studied, and there does not appear to be a major difference between the drugs. So the numbers here come from the trials of sildenafil.

Adverse effects were common, affecting about an additional 2 out of every 10 men taking sildenafil. The drug caused headaches and flushing in more than 10% of men who used it. Indigestion (dyspepsia) was an adverse effect for about an additional 5% of men (1 in every 20), and visual disturbances were caused in about an additional 3% of men.

These drugs have been shown to work in men with a variety of health problems, but the suitability of the drugs in any individual man’s case needs to be discussed with a doctor. In the trials, many men who had no success with one of the drugs were able to maintain an erection with one of the other drugs. There is not yet enough research on whether one of the drugs is better than the others.

Author: Institute for Quality and Efficiency in Health Care (IQWiG)

© IQWiG (Institute for Quality and Efficiency in Health Care)