Heroin users in Chicago are warned against the dangers of mixing in Fentanyl - a painkiller first synthesized in Belgium in 1950 and is 80 times stronger than heroin, according to DEA.

Fentanyl overdose is suspected responsible for hundreds of recent deaths around the United States, 130 deaths alone since January 2005 in and around Detroit.

Mixing a pinch of fentanyl with heroin has lately become the new fad to get an extra high among the heroin addicts, according to news reports.

According to The Chicago Recovery Alliance, you can tell the fentanyl-laced heroin from pure heroin by their color - the former has a minty green color whereas the regular heroin looks "yellowish or dusty brown."

Anesthetics and analgesic drugs containing fentanyl is marketed under different brand names including Sublimaze, Alfenta, Sufenta, Duragesic, and Actiq.

An especially dangerous form of fentanyl, about 10,000 times more potent than morphine, is marketed under the trade name Wildnil which is used to immobilize large and dangerous animals.

However chemical analysis of the fentanyl captured as evidence in the heroin-related deaths showed that it has nothing to do with the kind of fentanyl found in its prescription form.

Authorities have confirmed that this variant of fentanyl is manufactured in underground labs but they are still searching for the exact source.

Some reports point a finger at Mexico as the main source of fentanyl entering the United States.