FOR decades, antipsychotic drugs were a niche product. Today, they’re the top-selling class of pharmaceuticals in America, generating annual revenue of about $14.6 billion and surpassing sales of even blockbusters like heart-protective statins.

While the effectiveness of antipsychotic drugs in some patients remains a matter of great debate, how these drugs became so ubiquitous and profitable is not. Big Pharma got behind them in the 1990s, when they were still seen as treatments for the most serious mental illnesses, like hallucinatory schizophrenia, and recast them for much broader uses, according to previously confidential industry documents that have been produced in a variety of court cases.

Anointed with names like Abilify and Geodon, the drugs were given to a broad swath of patients, from preschoolers to octogenarians. Today, more than a half-million youths take antipsychotic drugs, and fully one-quarter of nursing-home residents have used them. Yet recent government warnings say the drugs may be fatal to some older patients and have unknown effects on children.

The new generation of antipsychotics has also become the single biggest target of the False Claims Act, a federal law once largely aimed at fraud among military contractors. Every major company selling the drugs — Bristol-Myers Squibb, Eli Lilly, Pfizer, AstraZeneca and Johnson & Johnson — has either settled recent government cases for hundreds of millions of dollars or is currently under investigation for possible health care fraud.