Fentanyl, about 50 times stronger than heroin, takes only two days to make, while heroin takes five months.
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.