SSRI's disrupt removal of serotonin from the synaptic cleft, over time causing a steady increase in free serotonin. While the drugs aren't 'habit forming' in the traditional sense they will often cause a rebound syndrome when they are discontinued. Stopping an SSRI abruptly causes a massive shift in the brains chemical equilibrium, essentially shorting it of the surplus neurotransmitters it's adapted to working with. The rebound leaves the patient with lower serotonin levels and a good two week shit slide of horrible symptoms until the brain can reconfigure itself. Known as SSRI discontinuation syndrome, it's known to occur even when patients are gradually weaned off their drugs.
Cannabis is mentioned in the same context because the cannabinoids also affect the serotonic system (though that is not the only neurotransmitter they affect) and long term inundation will cause a shift in neurochemical equilibrium that causes 'withdrawl symptoms' (ie your brain ran out of lubricant) after abrupt cessation. Interestingly endogenous cannabinoids are implicated in memory repression and regulation by inhibiting serotonic neurons, each time you spark up your essentially smoking a euphoric amnesiac.
Schizophrenia is thought to be caused by excessive dopamine concentrations in the mesolimbic cortex (amphetamine psychosis approximates schizophrenia, amps increase free dopamine concentrations.) The class of drugs used to treat schizophrenia, the major tranquilizers, work by reducing free dopamine concentrations in the brain. Schizophrenia and it's treatments aren't comparable to depression at all. The major tranquilizers are mighty dangerous drugs with high mortality rates. Patients have mandatory blood toxicity (this is for a specific drug, the name eludes me but it's one of the newer ones) tests each month to check if the drug is killing them. A pharmacist I know who dispenses these medications says that most schizophrenics would prefer to live with the increased mortality rate than remain untreated, self isolated meat sacks who can't cope with reality. Point being, "psychos" are real biological fuckups with real medical treatments to improve their quality of life, Don't lump all medical treatments in with anti depressants, it's the application not the science you should be opposing.
That said with regards to drugs bringing humans closer to reality, or maximizing the potential of our biological engines; hallucinogens don't bring us closer to reality. They take us into our heads, their therapeutic application is giving us a tool to analyze our internal paradigms and bring them into a state that better corresponds with reality. However most trips don't bring you closer to nirvana, it's just another form of (fun) intoxication. Advocating hallucinogens to maximize human potential is kinda like the argument for anti depressants; there are area's where they prove valuable but in the end its just another drug, a tool that can help you along the way but not a substitute for getting there on your own. Cut to Hunter S. Thompsons speech against the hippie counter culture from fear and loathing and trey azagthoth urging us to fulfil our potential..
However the racetam class of nootropic drugs appears especially promising in this regard: http://en.wikipedia.org/wiki/Piracetam