WASHINGTON (AP) -- Drug maker Eli Lilly is warning that tampering has been discovered on a few bottles of the psychiatric drug Zyprexa.

In letters sent to pharmacists and other health care professionals the company said that bottles have been found in which the pills intended for the treatment of schizophrenia were replaced with white tablets marked "aspirin."

The letters were posted on the Food and Drug Administration's Internet site Tuesday.

Lilly spokeswoman Marni Lemons said the first tampered bottle was discovered in Minnesota in January. That was investigated and thought to be an isolated case.

But two more bottles turned up last week in separate pharmacies in different parts of Wisconsin, prompting the warning letters, she said.

Lemons said the letters were faxed to 75,000 pharmacies across the country on Saturday and thousands more are being sent to health care professionals.

She said there have been no reports that any patients have been injured or that any tampered bottles made it past a pharmacist.

Nearly 9 million patients have been treated with Zyprexa over the last five years, Lemons said.

But the warning letters reminded drug dispensers to look carefully at the products they sell to make sure they are correct.

The tampered bottles contained 60 pills, labeled either 10 milligram or 15 milligram Zyprexa, the company said.

According to the letters sent to pharmacists, Zyprexa 10 mg tablets are round and white, similar to aspirin. But they are clearly marked in blue with the word, "Lilly" and the number, "4117" on one side, and no markings on the other side. Zyprexa 15 mg tablets are oval-shaped and blue and embossed with the word, "Lilly" and the number, "4415."

The letters asked pharmacists who find Zyprexa bottles that contain anything other than pills marked "Lilly" to immediately contact the notification center which coordinates recalls for pharmaceutical companies.

Patients who are suspicious about their Zyprexa subscription should return it to their pharmacy, the company said.

Copyright 2002 The Associated Press. All rights reserved.