according to the d.e.a., it's cut with phentynol. and to street very severe pain associated with cancer. >> so why phennynol. >> it gets into the brain very, very rapidly but it's so potent that very small quantities are needed to produce same high. >> and how much more potent would it be? >> so it's on the order of 20 times pore potent than heroin. >> in philadelphia last year, phentonol. people believe the deadly cocktail was most likely sold along kensington avenue. when you hear an uptick in deaths or they are cutting heroin with this phontonyl it's deadly. >> and it's very scary, because i have grown to love a lot of these people down here. >> it's this fear that keeps carol submitted to leading those who live in darkness into the light. >>> fast forward to what chicago is seeing now. for the second time this year, authorities there have issued a street alert after more than 20 people o.d.ed in just 24 hours. they do suspect that phentonyl they do suspect that phentonyl was behind this spike in deaths. >> next, warhol, lennon, o