Yet even though 25 percent of Americans suffer from a diagnosable mental illness in any year, there are few signs of innovation from the major drug makers.

After a series of failed clinical trials in which novel antidepressants and antipsychotics did little or no better than placebos, the companies seem to have concluded that developing new psychiatric drugs is too risky and too expensive. This trend was obvious at the 2011 meeting of the American Society for Clinical Pharmacology and Therapeutics, where only 13 of 300 abstracts related to psychopharmacology and none related to novel drugs. Instead, they are spending most of their research dollars on illnesses like cancer, heart disease and diabetes, which have well-defined biological markers and are easier to study than mental disorders.

To understand this predicament, it helps to know how we got here.

All of our current antidepressants, antipsychotics and anti-anxiety drugs share the same molecular targets in the brain as their prototypes from the 1950s. For example, the new antipsychotic drugs block dopamine receptors in critical brain regions, just like the first antipsychotic, Thorazine, synthesized in 1950. And all of our current antidepressants increase the levels of one or more of the neurotransmitters serotonin, dopamine or norepinephrine, just like the early tricyclic antidepressants.

With rare exceptions, it is hard to think of a single truly novel psychotropic drug that has emerged in the last 30 years. True, the new psychotropic drugs are generally safer and more tolerable than older prototypes, but they are no more effective. So why has the pharmaceutical industry churned out so many copycat drugs?

The simple answer is that we don’t yet understand the fundamental cause of most psychiatric disorders, in part because the brain is uniquely difficult to study; you can’t just biopsy the brain and analyze it. That is why scientists have had great trouble identifying new targets for psychiatric drugs.