After Justin Bieber opened up about his struggle with fame and addiction to "heavy drugs", several of his friends, including Miley Cyrus and Ed Sheeran, have come out in his support.

Earlier this week, the "Sorry" singer shared an Instagram post through which he reflected on how growing up in an unstable home and becoming a global star at 13 turned out to be physically and mentally stressful, leading to drug abuse and suicidal tendencies.

Celebrities, including Sheeran, Cyrus, Sean Kingston and Khloe Kardashian, left comments on his post -- some thanking him for sharing his story and some showing him love and support.

"Friends from the beginning, here until the end," Cyrus commented.

Khloe wrote: "This is beautiful! Thank you!! We are so proud of you!! I needed this! God bless you always."

"Wow thank you for the testimony. I sure needed this... God bless you forever my lil brother," posted Kingston, who collaborated with Bieber on "Eenie Meenie" in 2010.

"Love seeing this so much man! Wow," commented singer Cody Simpson, who collaborated with Bieber in 2014 on "Home to mama".

Miley's younger sister and singer Noah Cyrus also commented with three black-heart emojis. Sheeran posted a simple heart emoji on the post.

Juicy J wrote "God bless", along with three prayer-hands emojis, while Akon used the flexed-bicep emoji to comment on the post. Christina Perri thanked Bieber for "sharing this part of you".

Actor Patrick Schwarzenegger commented "Great message brother".

Actor Kyle Massey, who played Cory Baxter in the hit sitcom "That's So Raven" and its spin-off "Cory in the House", related to his message.

Massey posted: "This is so powerful. I experienced ups and downs in my life being a celebrity and the point of view of the child star is one most people and media ignore. It's a blessing to be apart of an industry like entertainment and growing up in it is a dream. my family and friends are the only reason why I have been able to keep myself true and down to earth and my head on straight. Thank you for this post Justin Bieber this just uplifted my day. Thank you for the love you spread. The world needs more of you. Never stop believing."

Bieber opened up about the hardships he endured as a child star through the post on Monday. He admitted to "doing pretty heavy drugs at 19 and (abusing) all of my relationships".

The star wrote that he "became resentful, disrespectful to women, and angry. I became distant to everyone who loved me and I was hiding behind a shell of a person that I had become".

Beiber was discovered while performing on YouTube aged 13 and soon amassed millions of fans but had several run-ins with the law and often made headlines for his controversial behaviour rather than his music.