This is sort of an urban myth put forward by the Scientologists. Like all urban myths, it has anectdotal evidence to support it.
Some people on Prozac have committed suicide, true, but often people who are suffering from depression commit suicide. Virtually everyone being treated with Prozac has some form of depression. If Prozac had been shown to have a causal link with suicide, it would be off the market.
Of course, Tom Cruise would disagree with that, but he eats placenta...
http://www.drugawareness.org/Archives/Survivors/survivor_index.html
I'm not a scientologist or believe it is a urban myth. Take a look at the site I provided.