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Viagra and similar drugs linked to rare form of amnesia

The Neuroshrink blog recently explored why Viagra and other medications used to treat erectile dysfunction can trigger an episode of transient global amnesia (TGA), “one of the more mysterious and freaky cognitive syndromes one can encounter.”
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The Neuroshrink blog recently explored why Viagra and other medications used to treat erectile dysfunction can trigger an episode of transient global amnesia (TGA), “one of the more mysterious and freaky cognitive syndromes one can encounter.”

“TGA isn’t like amnesia in the soap operas, where people awake after a coma or head injury and can’t remember their name or recognize their family,” writes the Neuroshrink blogger (an anonymous physician specializing in neuropsychiatry). “TGA is a brief episode of primarily anterograde amnesia, which is the inability to form new memories.”

Fortunately, TGA symptoms are not long lasting. They usually resolve within 24 hours, although people who experience the condition will not remember anything that occurred during the episode.

It’s estimated that each year about 3 to 5 people per 100,000 in the U.S. experience a TGA, although that number increases to 23 per 100,000 for people over the age of 50.

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This past summer, a second example of someone experiencing a TGA after taking an erectile dysfunction medication (Cialis in this case) and not having sex was reported in the medical literature.

The not having sex part is important. Sex (as well as vigorous exercise, exposure to cold, and strong emotional experiences) can trigger a TGA episode on its own. So although TGA has been listed for several years as a possible side effect on the labels of erectile dysfunction medications, many doctors have thought that sex, not the medication itself, was to blame for any episodes.

Here are the details from the published case study:

A 48-year-old man presented with sudden memory impairment. His medical history was relevant for mild dyslipidemia [elevated blood cholesterol] and long-standing impotence. [Cialis] had been prescribed for the first time the day before. After taking a 25 mg pill, and not getting an erection, he decided to sleep. He was not anxious, did not hyperventilate, and did not undergo any physical activity before sleeping. He woke up the next morning unable to remember things from the week before — such as the previous day’s medical consultation, that he had been installing new lamps in the house, or that a tree fell in his yard — seeming surprised and irritated every 5 minutes, and repetitively questioning his wife about this. He was otherwise normal, capable of dressing, cooking breakfast, and even driving to the hospital. … Memory abnormality started to gradually fade, with almost complete recollection of past events by the 8th hour after symptom onset, leaving memory gap for this period. Two days later there was only inability to recall what occurred in that morning.

Scientists don’t know with certainty what neurological mechanism sets off a TGA episode, but the two leading theories are seizures and vascular events (some change in blood circulation). Given the known vascular effects of erectile dysfunction medications (that’s how they work, after all) and the fact that they often cause headaches, the vascular theory seems the most probable, says the Neuroshrink blogger.

“It is most likely that whatever vascular changes lead to TGA involve the hippocampus, both because this is where short-term memories are encoded and also because there is some [magnetic resonance imaging] evidence that some TGA patients have slight tissue loss in one or both hippocampi,” he adds.

Don’t expect sales of erectile dysfunction drugs to flag on this news (although sales are down for other, probably economic reasons).

 “You might think that this is a major side effect that would discourage use of these medications,” writes the Neuroshrink blogger, “but I have a feeling that if men can ignore concerns about vision loss, cardiac events, and prolonged painful erections, [hearing loss, too — see here] then worries about transient global amnesia won’t begin to make a dent in their blockbuster sales.”