According to CNN, the three men and a woman were arrested during raids at several New York City apartments on Tuesday. Police say they recovered 350 bags of heroin. This comes as the investigation into Hoffman's death continues.
There are reports that a tip led police to the suspected drug dealers who allegedly supplied Hoffman with his heroin.
The 46-year-old Oscar-winning actor was found unconscious on the bathroom floor of his New York City apartment on Sunday. Officials say there was a needle in his arm.
Investigators found syringes, more than 50 bags of heroin and numerous prescription drugs in the apartment. They also discovered buprenorphine, a drug used to treat heroin addiction.
Police said Tuesday that the heroin recovered at Hoffman's apartment has tested negative for the powerful additive, fentanyl. The synthetic morphine has been linked to 22 suspected overdose deaths in western Pennsylvania.
Police have been investigating the actor's death as a suspected drug overdose. But an autopsy is being conducted to determine the exact cause of death.
Detectives are reviewing surveillance video to try to piece together Hoffman's activities in the hours leading up to his death. Officials said the actor made six ATM transactions for a total of $1,200 inside a supermarket near his home the day before his death.
At about 8:00 p.m. Saturday, Hoffman spoke with Mimi O'Donnell, the mother of his three children. That was the last known contact that Hoffman had. When Hoffman didn't show up the next morning to pick up his kids, his friend, David Katz, and another person checked on him and found him dead.
A private funeral is expected to be held Friday.
Hoffman appeared in 50 films in less than 25 years. He was nominated for an Oscar for his performances in "The Master," "Charlie Wilson's War" and "Doubt,"and won an Oscar for his leading role in the 2005 film "Capote." He also appeared in films such as "The Big Lebowski" and "Almost Famous" and "The Hunger Games: Catching Fire," as Plutarch Heavensbee.
ABC News and The Associated Press contributed to this report.