Tributes are pouring in following the death of actor Philip Seymour Hoffman at his home in New York on Sunday.
The Oscar-winning actor, 46, was found by a friend who called emergency services. He was declared dead at the scene.
A police spokesman said investigators found two small plastic bags and a substance suspected of being heroin.
Robert De Niro was among many fellow actors expressing their sorrow, describing him as "a wonderful actor".
"I'm very, very saddened by the passing of Phil. He was a wonderful actor. This is one of those times where you say: 'This just shouldn't be'," he said.
In a statement, his family said: "We are devastated by the loss of our beloved Phil."
Hoffman is survived by his partner Mimi O'Donnell, and their three children.
Jennifer Lawrence, who starred with Hoffman in The Hunger Games, described him as an "such a incredible actor".
"You played an excellent Plutarch. So sad," she wrote.
Julianne Moore, who co-starred with Hoffman in Boogie Nights, Magnolia and The Big Lebowski, said: "I feel so fortunate to have known and worked with the extraordinary Philip Seymour Hoffman, and am deeply saddened by his passing."
George Clooney, who appeared alongside Hoffman in The Ides of March, said: "There are no words... It's just terrible."
Philip Seymour Hoffman
1 best actor Oscar for Capote, 2005
3 supporting actor Oscar nominations
51 feature film releases, 1991-2014
29 dramas, 21 comedies, 1 animation
4 real life characters played: Lester Bangs, Truman Capote, Art Howe, Gust Avrakatos
The actor Ken Stott, who became friends with Hoffman while making Charlie Wilson's War, described the actor as "compelling" on BBC Radio 4's Today programme.
"It was a real shock. We were always in touch... he demanded respect, he had a quiet, friendly attitude to his work."
When asked about the circumstances of Hoffman's death, Stott said: "This event I believe to be misadventure."
Director Mike Nichols, who directed Hoffman in Charlie Wilson's War and in Death of a Salesman, said: "No words for this. He was too great and we're too shattered."
Kevin Costner told the Associated Press: "Philip was a very important actor and really takes his place among the real great actors. It's a shame.
"Who knows what he would have been able to do? But we're left with the legacy of the work he's done and it all speaks for itself," he added.
Hoffman had candidly spoken in the past of his struggle against drug addiction, including a 2006 interview in which he told CBS he had at times abused "anything I could get my hands on. I liked it all".
Comedian and actor Steve Martin praised Hoffman's 2012 Broadway performance in Arthur Miller's Death of a Salesman.
And Gary Oldman told Sky News: "He was on a list of mine as an actor to work with and hoped to be directing.
"He had that little bit of danger to him and vulnerability to him, all those qualities that I think make somebody watchable and very special."
Kevin Spacey tweeted: "A tragedy to lose as supremely talented an actor as Philip Seymour Hoffman. An unspeakable loss for film, theatre & all who knew him. RIP."
Hoffman won a best actor Oscar in 2005 for Capote and was nominated a further three times - for The Master, Doubt and Charlie Wilson's War.
He also picked up three Tony nominations for his work on Broadway, including Death of a Salesman.
One of his earliest movies was Scent of a Woman in 1992 and he had a breakthrough role as a gay member of a porn film crew in Boogie Nights, directed by Paul Thomas Anderson, who he also collaborated with on other films including The Master.
According to the Hollywood Reporter, Hoffman had completed his work for The Hunger Games: Mockingjay Part 1, and had only seven days remaining to shoot on The Hunger Games: Mockingjay Part 2.
It is thought the films' scheduled release dates of 21 November 2014, and 20 November 2015, respectively, will not be affected by Hoffman's death.
He was also set to star in his first major TV series, Happyish, for Showtime but the Hollywood Reporter said the series was not yet in production.
Showtime issued a statement following the news of Hoffman's death, saying: "Philip Seymour Hoffman was one of our generation's finest and most brilliant actors. He was also a gifted comedic talent.
"It was a great privilege and pleasure to work with him and we are all absolutely devastated by this sudden loss. Our thoughts go out to his family at this very difficult time."
Meanwhile, Screen Daily reported that Ezekiel Moss, to be directed by Hoffman, will not now be presented as planned at the European Film Market in Berlin this week.
The Prohibition-era film was to star Jake Gyllenhaal and Amy Adams.
"Exclusive Media is deeply saddened to learn the shocking news of Philip Seymour Hoffman's passing," the company said in a statement.