In the film "Requiem for a Dream", what drug does Jared Leto's character get addicted to?

In the film "Requiem for a Dream," Jared Leto's character, Harry Goldfarb, gets addicted to Heroin. This particular drug is portrayed in the movie due to its potent and highly addictive nature, which accurately reflects the dark and destructive themes explored in the film. Heroin addiction showcases the characters' downward spiral, further emphasizing the devastating consequences of substance abuse and the insidious grip it can have on an individual's life.