Eli Lilly and Company's schizophrenia drug, olanzapine (or, known for its brand name, Zyprexa, Zyprexa Zydis, or in combination with fluoxetine Symbyax), causes excessive sleepiness in some patients when used in a special long-acting form called Zyprexa Adhera.

Olanzapine was known to be highly sedating and the usual recommendation, even for the normal formulation, was to take the drug one time a day before going to bed. It is also associated with significant weight gain.

"We found additional risk that didn't exist with oral administration, of sedation," said Sara Corya, medical director for Eli Lilly, in an interview with Bloomberg News. "Some sedation is a well-known side effect of Zyprexa in general, as with many medications."

The Zyprexa Adhera tried to solve a common problem in treating psychosis: patients don't adhere to the treatment. Thus the "Adhera" is a monthly or twice a month injection which slowly releases the drug into the patient's system. U.S. regulators with the Food and Drug Administration said that there was a relatively high incidence of excessive sleepiness compared with the oral form of the drug.

This may also be caused by improper injection in a blood vessel instead of the muscle. The drug may have, this way, entered the system at a much higher rate than desired, causing essentially an overdose. The regulators said that the sedation typically lasted about one to three hours and affected about 1 percent of patients given the injection.

Olanzapine was approved by the FDA for the treatment of schizophrenia in 1990, then for depressive episodes associated with bipolar disorder, as part of the Symbyax formulation, in 2003 and acute manic episodes and maintenance treatment in bipolar disorder in 2004.

The drug's Adhera form is currently under review by the FDA. The company, Lilly, will lose monopoly over olanzapine in 2011 and struggles to develop new uses for the drug which may continue to bring it strong profits.

Schizophrenia affects around 1 percent of Americans. The illness is characterized by impairments in the perception or expression of reality which may take different forms. There is no laboratory test for schizophrenia, it is diagnosed based solely on the patient's self-reported experiences and observed behavior by the healthcare professional.