According to a bbc article,
"People who drink too much coffee could start seeing ghosts or hearing strange voices....."
The article goes on to say that a new study shows that people who drank more than seven cups of instant coffee a day were three times more likely to hallucinate than those who drank just one cup.
I've never heard of anything so preposterous.
Coffee is completely harmless.
I know because the flying Folgers can told me so.