Federal health regulators have issued enforcement letters to Eli Lilly and Co., Bayer, Amylin Pharmaceuticals and Cephalon for making inaccurate or incomplete statements while promoting their drugs.

The Food and Drug Administration on Tuesday disclosed four letters issued to the companies by its marketing enforcement division.

The letter to Indianapolis-based Lilly cites a print advertisement for the antidepressant Cymbalta, which is approved to treat depression, generalized anxiety disorder, diabetic nerve pain and the pain ailment fibromyalgia. According to the FDA, Lilly's ad did not adequately display information about the drug's side effects, a requirement for all pharmaceutical promotions.

The company said it is working to remove the materials from marketing circulation.

"Lilly is committed to providing clinically accurate and balanced promotional materials to health care professionals and patients," the company said in a statement.

The FDA's letter to Cephalon, based in Frazer, Pa., makes similar complaints about missing risk information in the company's promotional cards for Treanda, a lymphoma treatment.

The FDA says the card is "false or misleading because it omits important risk information." The drug has been linked to serious infections, skin reactions and other side effects.

A spokeswoman for Cephalon said the company has instructed sales people to stop using the card. The company has already responded to FDA's concerns and is also reviewing all marketing materials for Treanda, she added.

In the letter to Amylin, regulators take issue with statements made by the company while promoting its diabetes drug Byetta at a conference in Washington D.C. last summer. According to the letter, several statements promoted the drug for unapproved uses and "overstate the efficacy of Byetta."

San Diego-based Amylin co-markets Byetta with Lilly.

The companies said in a joint statement that they have already responded to FDA's letter and, "will take action as needed in order to ensure all product communications adhere to regulatory requirements."

Similarly, FDA reviewers said Bayer's script for a presentation on its birth control implant Mirena "overstates the efficacy" and "presents unsubstantiated claims," according to the letter.

A spokeswoman for Bayer Healthcare Pharmaceuticals said the company discontinued the promotional program last February. She confirmed that the German conglomerate's drug unit, based in Wayne, N.J., received the letter Dec. 30 and will respond by Thursday Jan. 14, as requested by FDA.

The four letters were issued on separate dates between mid-December and early January.

The FDA regularly issues letters to companies that do not follow regulations for manufacturing and marketing.