Mexico drugs: Fentanyl takes over heroin market

The synthetic opioid fentanyl is causing a crisis in the United States, where tens of thousands of overdoses are recorded each year.

But in Mexico, it is also altering the internal drug market.

Traffickers are increasingly smuggling the new drug, instead of locally grown heroin, making poppy farming virtually worthless.

Al Jazeera’s John Holman went to the hills of Sinaloa to find out more.