Money, money, money: Big profits drive cartels' fixation on fentanyl

Fentanyl was created in the 1960s as a legitimate drug to treat pain in cancer patients and others.

Yet over the past decade, an illicit form has shown up in the U.S. drug supply as Mexican cartels convert precursor chemicals, often from China, into synthetic opioids and mix it with other drugs.

Fentanyl made in clandestine labs has proven to be highly deadly and is increasingly found in a range of drugs beyond heroin, including cocaine and fake prescription pills.