Rush (1991)

Raynor is an undercover narcotics cop. For his next assignment he chooses the more inexperienced but tough and good-looking Kristen. Their ultimate target is Gaines, a renowned but very elusive drug dealer. While doing their work they unexpectedly fall into a morass of drug-addiction and fall in love with each other. Despite subjecting themselves to the life of low-class, one-track junkies they do not get the evidence they want to convict Gaines, and instead are forced into using false evidence in court.