How Fentanyl became the most dangerous illegal drug in America

Fentanyl is a synthetic opioid used widely in hospitals as a powerful painkiller.

Since the late 1960s, it's been one of the world's most important opioid analgesics.

But in the United States illegal fentanyl use has exploded, last year it killed over 70,000 people.

We examine the global supply chain and why fentanyl is unlike any other drug problem in history.