To complete this side quest you will need to search 3 pharmacies in the Slums.
The first on is right on the corner of a street just south of the tower, near Dr. Zere's place.
The other one is a pharmacy with a metal-caged roof covered in plans, it has to be accessed through the roof. Behind the pharmacy is a ambulance car. It is somewhere west-southwest of the tower.
The third pharmacy is right down the street right next to the safe zone where the "Psycho" challenge is.