Jamie is heavily addicted to cocaine and alcohol in the movie.
The film's primary theme is addiction. So, we see cocaine being snorted several times throughout the film including a scene where Michael J Fox does lines on a coffee table and another where he gets a nosebleed from his cocaine abuse.
Alcohol is regularly consumed in clubs, parties, and other social venues. Jason Robards' character is in a state of severe inebriation every moment he is on screen even to the point where he seems to be hallucinating at times and babbles incoherently and talks with slurred speech. Fox's character has a drunken moment or two.
Cigarettes are smoked in some scenes.