From Mexico cartel safe house to US streets: BBC tracks deadly fentanyl targeted by Trump tariffs

Fentanyl is 50 times more potent than heroin and 50 times harder to make and transport.

US President Donald Trump has introduced a 25% tariff on all goods from Mexico in response to what he says is the unacceptable flow of illegal drugs and illegal immigrants into the US .

The BBC gained rare access to a cartel's operation along the Mexican border and travelled to the US to meet their ultimate customers.

Philadelphia 's Kensington neighbourhood is dubbed the largest open-air drugs market on the US east coast.

Rosalind Pichardo of Operation Save Our City records the number of times she has reversed an opioid overdose using the quick-acting drug Naloxone.

For the past six years , the figure totals 2,931 . She records the roll-call of fentanyl victims, and that number written in red comes alive with the memories of the individuals she saved.

Roz Pichardo holds out little hope that even if the fentanyl trade is cut off from Mexico that it will improve people's lives in Kensington .

"The problem that we have with the war on drugs is - it didn't work then [and] I don't believe it's going to work now," she says.