Researchers say they are surprised that neuroticism and extraversion -- 2 of the 5 basic personality traits that they thought were basically immutable -- are affected by anti-depressants; people get less neurotic and more extraverted. People often get slowly more extraverted with age, but this happens with the speed of medication. (Abstract)
This is only mildly surprising. If you believe, as I do, that big chunks of personality are biologically determined, then if you change the parts of biology that make you depressed, you would expect to change the personality. Anti-depressants act by increasing seratonin in the brain.