Thriller. Two students have their memory erased after a failed drugs trial. Read in 1990s.

[maddie]

My mother read this book in the 90s, but we’re not sure when it was published. She says it's a thriller about a male and female student who were in a relationship and participate in a clinical drugs trial that kills the other participants. However they survive but have their memory erased. Years later, the male student starts to experience flashbacks and goes to look for the female student.