Drug giant Eli Lilly has engaged in a decade-long effort to play down the health risks of its top-selling medication, the schizophrenia drug Zyprexa, The New York Times reported in Sunday editions.

Citing hundreds of internal Lilly documents and e-mail messages among top company managers provided by a lawyer representing mentally ill patients, the Times said Lilly executives kept important information from doctors about Zyprexa’s links to obesity and elevated blood sugar, risk factors for diabetes.

The drug company’s own published data, which it told sales representatives to play down in conversations with doctors, showed 30 percent of patients taking Zyprexa gain 22 pounds or more after a year on the drug, with some reporting gaining 100 pounds or more, the Times said.

The documents, which cover 1995 to 2004, indicate Lilly’s concern that Zyprexa sales would suffer it was more forthright about the drug’s risk of causing unmanageable weight gain or diabetes.

Lilly denied in a written response to the documents that its drug is more likely to cause diabetes than other widely used schizophrenia drugs, and defended its safety, saying the documents, release of which it called illegal, had been taken out of context.

“In summary, there is no scientific evidence establishing that Zyprexa causes diabetes,” the company told the paper.

Lilly said it had given the FDA all its data from clinical trials, reports of adverse events and data from literature reviews and large studies of Zyprexa’s real-world usage.

With sales of $4.2 billion last year, Zyprexa is by far Lilly’s best-selling product, with some two million people worldwide taking it, the Times said.

The Times said the documents show the company worried about the drug’s side effects as early as 1999, and their potential to hurt sales.

“Olanzapine (its chemical name) associated weight gain and possible hyperglycemia is a major threat to the long-term success of this critically important molecule,” Dr. Alan Breier, now Lilly’s chief medical officer, wrote in a November 1999 e-mail to two dozen Lilly employees, the Times reported.

And Lilly’s marketing research found in 2000 and 2001 psychiatrists consistently said many more of their patients developed high blood sugar or diabetes while taking Zyprexa than other antipsychotic drugs, according to the report.

The documents were collected as part of lawsuits on behalf of mentally ill patients against the company, the Times said.

Lilly agreed in 2005 to pay $750 million to settle suits by 8,000 people who claimed they developed diabetes or other medical problems after taking the drug; thousands more suits are pending.

The documents were provided by James Gottstein, a lawyer representing mentally ill patients who is suing the state of Alaska over its efforts to force patients to take psychiatric medicines against their will.