Microdosing was the process of administering a low dose of a drug or medicine which would be unlikely to produce large physiological changes.
San caused Emperor Philippa Georgiou to believe he had died by poison, but in the early 24th century revealed to her that he had built up an immunity to the poison through small doses. (Star Trek: Section 31)
In 3189, a truth serum was ineffective at compelling Cleveland Booker due to him being well-acquainted with microdosing. (DIS: "That Hope Is You, Part 2")