Home > Cases, neurology, News > Another Viagra Side Effect: Amnesia

Another Viagra Side Effect: Amnesia

By Soman via Wikimedia

It sounds like the setup for an off-color joke, but it’s true: Viagra and the other phosphodiesterase inhibitors (definitely Cialis, and probably Levitra too) 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. TGA is a brief episode of primarily anterograde amnesia, which is the inability to form new memories. The soap opera amnesia is retrograde amnesia, where past events are not recalled but the character can learn (or relearn) and rebuild an identity. Transient global amnesia can also involve retrograde amnesia but past events prior to the onset of amnesia are generally recalled without much difficulty. TGA resolves on its own, typically over the course of a few hours to a day, and usually doesn’t recur.

One of the most interesting things about TGA is that, although it has been well-described for decades, there is no real agreement about how it happens. There are well-described triggers: vigorous exercise, exposure to cold, strong emotional experiences, and sexual intercourse. There have been several reports of TGA after use of medication prescribed for erectile dysfunction (Viagra, etc.) but since there was also sex involved, the medication itself wasn’t considered a trigger. There have now been, however, two cases published where someone had TGA after taking an ED medication and NOT having sex.

Generally, theories about TGA fall into two categories: seizure and vascular events. Given the nature of the known triggers, and the known vasodilatory effects of ED medications, these reports would seem to favor a vascular explanation. We do know that Viagra and its kin have vascular effects that encourage erections (after all, that’s the point) but they often cause headache as well, implying that they are also vasoactive in the head.

Bob Dole, Viagra pitchman

TGA is a fascinating syndrome to observe and diagnose. Sufferers typically are somewhat anxious and aware that they are experiencing something unusual. Characteristically they will ask the same questions repeatedly: usually asking why they are in the hospital, how they got there, or what they did that day. They rarely become agitated, which is somewhat surprising until you realize that to become agitated one must hold onto the idea that something is wrong or upsetting. Patients with TGA are easily reassured, for a few seconds or minutes at a time. Gradually, they can hold information for longer and longer periods until their memory is essentially restored. They do not regain memory for events that happened during the episode. 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 MRI evidence that some TGA patients have slight tissue loss in one or both hippocampi. The best thing about TGA, compared to most things a neurologist or psychiatrist will see in the Emergency Department, is that the prognosis is excellent. Most patients are entirely  back to themselves within a day, and most will not have a repeat episode. In the past it was believed that the recovery was uniformly complete, but some studies that follow TGA patients indicate some residual but subtle cognitive impairments. TGA is fairly rare: Dr. Wikipedia gives the annual incidence in the USA as about 3 per 100,000, but that increases to 23 per 100,000 among those over 50.

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

  1. September 23, 2010 at 9:08 am | #1

    One day I will write a paper called “Why does Viagra cause TGA? An attempt to resolve the ‘hard problem’ of neuroscience”.

    Incidentally, it strikes me that TGA has a lot in common with the amnesia typically seen following ECT: people don’t remember the ECT session, and often don’t subsequently remember much about the surrounding few days.

    That could suggest a seizure etiology of TGA, but not really, because in ECT you get a grand mal seizure, wheras in TGA you generally don’t.

    • September 23, 2010 at 4:48 pm | #2

      The comparison with ECT is valid, but not because TGA is caused by a seizure. The reason for the retrograde memory loss in ECT is that the temporal lobe seizures involve the hippocampus. In my simple-minded way of thinking of memory, the hippocampus is where working memory is processed before becoming long-term memory. Having a temporal lobe seizure basically wipes whatever information was in the hippocampus that wasn’t stored and is therefore lost forever. I have had several patients become angry with me when waking up after ECT, not upset about memory loss, but angry because they didn’t believe me that they had already had their treatment.

      Why the hippocampus is preferentially affected in TGA is not clear, but it appears that whatever reduction in perfusion (from venous congestion?) causes the TGA is pretty specific for hippocampus. The neurological exam is generally normal in TGA, and other cognitive functions like language are also largely intact.

  2. September 24, 2010 at 5:47 am | #3

    Right. What’s interesting about ECT is that the actual seizure is so brief, the EEG returns to normal within a minute, but the amnesia period can be hours or days. Which suggests that there’s something about the hippocampal system which makes it especially “touchy” – if it goes wrong it takes a long time to get back to normal.

    In other words, whatever initially goes wrong in TGA, it might all be over by the time the symptoms present. which will make studying it tricky.

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    • Heather
      February 21, 2014 at 1:43 pm | #7

      Have you seen cases of TGa that would otherwise be classic but last more than one day. My father has what appears to be TGA with anterograde amnesia and some recent retrograde amnesia but its been a week! MAybe some improvement but not really. He is perseverating and questioning and it seems so classic. Normal MRI. Normal EEG. ONly clue is what appears to be new paroxysmal afib.

  6. March 25, 2014 at 10:17 am | #8

    I wonder how TGA affects job performance at place of employment. Obviously, it could lead to problems where, in time, employees could get fired (lose their jobs) because they did not get lucky or those drugs did not work at the time. Loss of job (unemployment) would then lead to unaffordability of the drugs and unhappiness. And when people are unhappy, it means they will be more prone to anger. This is a very scary scenario!! :-(

  7. March 31, 2014 at 3:29 am | #9

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  1. September 24, 2010 at 1:10 pm | #1

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