Just encountered this on PS4. It's very frustrating because it means that my Journal is now forever showing an unviewed quest with no option to clear it (why isn't there a "Set all as viewed"? option for the Journal and Codex, anyway?). I spoke to the doctor about the medicine before encountering the drug chemists and scanning the plant and when I looked at my Journal I realised that the quest entry was bugged.
I was unaware of the Doctor needing new medicine until the quest log triggered when i picked up the plant from a distress call from raiders in the area. I got the samples by giving them the UV lights and the journal said i had to hand it to a DOctor who needed it on Kadara, but i have absolutely no idea who that is or where that is due to the shoddy map and lack of minimap on screen...
