Memento (Warning) is a young adult novel with reporting elements, written by Czech author Radek John and published in 1986. The story is set in Prague in the 1980s. It was made into a film for Czechoslovakian television in 1990

The novel is written with literary language with elements of argot and slang of drug addicts. It is a subjective narration from the point of view of Michal, the main character. The author wanted to warn the public of rising drug problems in present days. Its importance lies in the fact it is the first work concerning this taboo theme in the time of the previous totalitarian communist regime in Czechoslovakia. The situation at that time was that the number of addicts was growing, but it had not been publicly discussed. It warns that escaping from problems through drugs will end badly.