The Dark Side of Viagra: Erectile Dysfunction Drugs And Vision Problems

According to published reports, the FDA has received 50 case reports of blindness and vision loss with sildenafil (VIAGRA), the first drug approved to treat erectile dysfunction (ED). The Food and Drug Administration (FDA) is conducting an investigation into the connection between sildenafil and the condition known as non-arteritic anterior ischemic optic neuropathy (NAION), which can cause blindness. Similar invesigations are also being made into vardenafil (LEVITRA), and tadalafil (CIALIS). A smaller number of reports have been received for vardenafil and tadalafil, which are newer to the market.  

The FDA approved sildenafil in March 1998. At that time, we invoked our Five Year Rule. The Five Year Rule became the Seven Year Rule after new data showed that the majority of drug withdrawls and safety-based label changes occurred within seven years of a drug’s release (see Worst Pills, Best Pills News June 2002).

The FDA approved vardenafil in August 2003. Tadalafil was approved in November of that same year. The Seven Year Rule applies to both vardenafil and tadalafil.

The original 1998 professional product labeling, or package insert, for sildenafil stated that in some studies, as many at 11 percent of men using the drug experienced abnormal vision. A color tinge was the most common report, but increased sensitivity to light and blurred vision were also reported.  

Shortly after the FDA’s reviews of the drug were made public in 1998, Public Citizen petitioned the FDA to make major changes to the drug’s professional product labeling. This petition focused on important safety issues seen with use of the drug in studies conducted before approval, including vision problems.   

Sildenafil works by inhibiting an enzyme called phosphodiesterase. Forms of this enzyme are found in many parts of the body, including the eye. Some scientists think that changes in this enzyme can lead to some types of a serious disorder called retinitis pigmentosa, which can cause retinal degeneration and loss of vision. Phosphodiesterase controls the level of a particular chemical messenger in the retina by breaking it down as it is formed. This function is extremely important. High levels of this chemical messenger can damage the retina of the eye, leading to eventual blindness.

Visual disturbances were reported in studies of sildenafil that Pfizer submitted to the FDA to support the drug’s approval. In one single-dose study that tested doses of sildenafil ranging from 100 to 800 milligrams, about half of the men taking doses greater than 100 milligrams experienced visual disturbances. (Sildenafil is approved to be prescribed in doses of 25, 50 and 100 mg.) The disturbances included difficulty seeing in dim light, color aberration, and color tinges. Another study of sildenafil in healthy male volunteers showed that starting at 100 milligrams, men taking the drug had difficulty differentiating between different colors that increased as the dose of the drug increased.

A third study looked at visual function in eight normal males and eight men with diabetic retinopathy, a serious eye condition seen in diabetics. Both groups were given either 200 milligrams of sildenafil or a placebo. In the sildenafil group, a test called the photopic electroretinogram (ERG) showed a 50 percent reduction in the response to blue light at 1.25 hours and at five hours after taking the drug.

In the petition, we noted that a 125-pound man taking 100 milligrams of sildenafil would be getting twice the dose per pound as a 250-pound man taking the same dose.

Public Citizen wrote a letter supplementing the petition to the FDA on August 20, 1998 . In it, we again noted that sildenafil works by blocking the enzyme phosphodiesterase and the potential effects of phosphodiesterase inhibition.

The letter noted several important unanswered questions about sildenafil. When sildenafil is taken repeatedly, will the chemical messenger regulated by phosphodiesterase rise to toxic levels in some individuals, incurring the potential for retinal damage? How will vision be monitored in people using the drug? Will those with pre-existing retinal diseases be at increased risk of further retinal damage? The letter  asked that the FDA immediately convene an advisory committee to review the various serious problems related to the use of sildenafil.

The editors of the highly respected Medical Letter on Drugs and Therapeutics, written for physicians and pharmacists and noted for their independence from drug company influence, reviewed vision loss associated with the use of sildenafil in their June 20, 2005  issue. The Medical Letter editors reported that 14 cases of vision loss associated with use of sildenafil have been published in the medical literature. All of these men experienced NAION with blurred vision, a loss of the ability to see in particular parts of the eye, or both.

In some of these men, the loss was progressive and occurred over days or weeks. The loss of vision was generally first noticed within 24 hours of taking 25, 50 or 100 milligrams of sildenafil. Some had been using the drug for months or years; others had taken only one or a few doses. Five men noticed the loss of vision on awakening the next morning. Four others noticed vision loss within 90 minutes of taking the drug. One patient had vision loss in both eyes. Vision loss due to NAION was partial but permanent, which is the usual outcome with this condition.  

The Medical Letter editors also noted that NAION had also occurred in a few men taking tadalafil. In one case, the patient reported that transient visual field loss occurred with the first four doses of the drug, and became permanent after the fifth dose.

The editors concluded:

“Acute loss of vision due to NAION has been reported in some men taking sildenafil (Viagra), but there is no proof of cause and effect.”

This conclusion is scientifically appropriate, since postmarketing and published case reports do not prove a cause and effect relationship. However, despite the absence of “gold standard” proof that sildenafil, vardenafil, or tadalafil cause NAION and possible blindness, the reports of NAION associated with the use of these drugs in conjunction with the FDA investigation mean that there is every reason to warn men of the possibility of harm from the use of these drugs. This is true for drugs that do not treat life-threatening conditions and especially true in the case of the erectile dysfunction drugs, which may be used for recreational purposes at higher than the FDA-approved doses.

What You Can Do

You should not use sildenafil, vardenafil, or tadalafil for recreational purposes because there is no medical benefit to be gained. The possible harm from these drugs, no matter how small, will always outweigh a lack of medical benefit. If you experience any visual problems while using these drugs, notify your doctor immediately.