Some of the characters in the film were played by actual New York City junkies at the time, people who Writer and Director Ivan Passer encountered while researching the film.
Paula Prentiss received top billing, even though she appears on-screen for about three minutes. When asked about this at the New York Film Festival press screening, Ivan Passer said that her agent demanded it, adding, "After all, what difference does it make?"
According to Ivan Passer, Robert De Niro was nearly fired many times throughout shooting. A devoted Stella Adler student, he would do things to exceptionally define his secondary character that would draw attention away from the leads.
When Ed Madsen is chasing George Segal down the hallway, he slips and falls. This was not written in the screenplay. However, Ivan Passer thought it looked so real, he decided to leave it in.
David Scott Milton based the characters in this film on the addicts who frequented the Manhattan diner he owned. He then adapted his observations of these characters into an off-off-off Broadway play called "Scraping Bottom."