Kate McKinnon was originally announced in the lead role but dropped out due to a scheduling conflict and Amanda Seyfried replaced her.
In the last scene of the episode "Old White Men", there's a brief shot of Kevin Hunter idly running his finger along the proprietary security tape on the Edison blood tester. This hints at an actual event cited in the series' source novel, where Hunter tried unsuccessfully to get permission to open up one of the blood testers and see if it was actually capable of testing blood.
The scenes where Elizabeth Holmes attends Stanford were actually shot at UCLA.
Linda Tanner, played by Michaela Watkins, was a character created for the show. She was based largely on Heather King, a member of Theranos' legal team brought on by David Boies, but she's also a composite of several Theranos employees.
By the fourth episode, Amanda Seyfried was wearing Elizabeth Holmes' signature black pantsuit and high-heeled shoes. Seyfried found the shoes extremely uncomfortable and frequently took them off during breaks in shooting.