Meperidine (also known as Demerol) was a type of pain killing drug widely used in the 20th century, and into the 21st. Because of its side effects, including neurological effects, it fell out of favor as an analgesic by the early 21st century. However, it continued to be used as part of a drug regimen used to "wipe" the memories of criminals and those who inadvertently learned state secrets.
The CSS Delphinus carried a large supply of Demerol which Dr. Elizabeth Dehner used to make the humans who encountered a pair of Vulcans and a team of temporally displaced Starfleet officers in 2045 forget these meetings. (TOS novel: Strangers from the Sky)