here's mariana van zeller. >> reporter: five years ago, almost no one had heard of it.oday, it's a household name. fentanyl. >> reporter: in the u.s., fentanyl is helping drive overdose deaths to record highs. >> it's wiping out a generation. >> reporter: while in mexico, it's disrupting the drug trade in ways not seen in generations. but few people understand how the cartels are getting their hands on the chemicals necessary to make fentanyl or what the fallout will be if they continue to churn these raw ingredients into deadly pills and powders. >> reporter: from mexico's cartel country to the border and into american communities, i'm going deep inside the fentanyl pipeline to see exactly how it's fueling the most devastating drug epidemic in u.s. history. >> reporter: in just a few years, fentanyl has become the most popular synthetic opioid on the streets. and mexico's cartels have stepped up to supply this demand. but it's a little-known secret that the cartels can't make the drug themselves. they first need to source these potent chemicals from somewhere or someon