Flowers for Algernon (Wikipedia)
This comes as a short story, or in extended format as a book.
HEre's aynopsis of the short story, taken from Wikipedia -
In the short story, Charlie Gordon is a 37-year-old man with an IQ of 68 who works as a janitor at Donnegan's Plastic Box Factory. He has surgery to increase his intelligence, following a similar successful experiment on Algernon, a laboratory mouse. The surgery is successful and Charlie's IQ triples.
Charlie falls in love with his former teacher, Miss Kinnian, but as his intelligence increases he passes her level and they are unable to relate to one another. As Charlie's intelligence peaks, Algernon unexpectedly loses his increased intelligence and dies. Charlie discovers that his intelligence increase is also only temporary. Unable to do anything to prevent the change, Charlie reverts to his original mental state in a swift reversal of his original growth. He tries to return to his original life and job at the plastic box factory but cannot stand everyone feeling sorry for him so he decides to move away.
I found this to be a very insightful, philosophical, and psychologically profound story, which I would recommend to anyone who feels interested in thought.
I've recently got myself the book, so I look forward to reading it soon.