Between early April 2005 and late March 2007, 1,013 Americans died after taking an overdose of an illegal version of the painkiller fentanyl, according to a report released on Thursday by the Centers for Disease Control and Prevention.

However, according to the study, the number of deaths has decreased after a fentanyl operation in Toluca, Mexico was shut down by authorities in May 2006 and cases of deaths provoked by overdosing on illegal fentanyl are not frequent anymore.

Dr. T. Stephen Jones, the study’s lead author said that such cases disappeared almost completely, mainly due to the shutting down of the Toluca facility.

The report was published in this week’s issue of the CDC’s Morbidity and Mortality Weekly Report.

Fentanyl is a prescription painkiller, regularly recommended to cancer patients and administered through a patch. Nonetheless, it is very potent, inducing euphoria and is 30 to 50 times more powerful than heroin.

Illegally manufactured versions of the drug are sold in the form of powder and are usually combined with cocaine or heroin, sometimes replacing heroin use. Some experts explain that numerous heroin addicts may be unaware that fentanyl is included in their injection.

The latest outbreak was first noticed in Chicago. Patients who recuperated from overdoses said they had been offered free heroin packed in orange and pink plastic bags by new drug dealers attempting to draw more customers. The Chicago cases are reviewed in this month’s issue of Clinical Toxicology.

National health statistics prove that the death rate from accidental drug poisonings almost doubled from 1999 to 2005.