The rise in the use of antidepressants in Britain could be threatening shrimp populations across the coast; scientists have found that shrimp exposed to fluoxetine (i.e., Prozac) concentrations similar to those in waste water are
more likely to be fatally overconfident, swimming towards light where they'd be easier prey for predators.
The evolutionary psychiatrist Randolphe Nesse infamously claimed that the widespread use of Prozac was skewing the stock market in a similar way, ie creating bubbles by making traders unrealistically optimistic. (It's a short, interesting article - text is at http://www.edge.org/3rd_culture/story/100.html)