The US pop star, 25, shared a post on Instagram where she said she had "always been transparent about [my] journey with addiction".
"This illness is not something that disappears or fades with time," she continued. "It is something I must continue to overcome and have not done yet.
"I want to thank God for keeping me alive and well. To my fans, I am forever grateful for all of your love and support throughout this past week and beyond. Your positive thoughts and prayers have helped me navigate through this difficult time."
She also thanked her family, team, and staff at the Cedars-Sinai hospital in Hollywood where she was treated following the reported overdose: "Without them I wouldn't be here writing this letter to all of you."
Lovato said she now required time to "heal and focus on my sobriety and road to recovery... I look forward to the day where I can say I came out on the other side".
"I will keep fighting," she concluded.
Lovato, who is one of the biggest-selling pop artists of her generation, has enjoyed global hits including "Cool For The Summer", "Sorry Not Sorry", and her recent UK. No.1 with Clean Bandit, "Solo".
She rose to fame on Disney Channel shows such as the film Camp Rock, alongside the Jonas Brothers, and Sonny With A Chance, before embarking on a solo pop career.
She has been vocal about her struggles with substance abuse and revealed she first tried cocaine aged 17, in a YouTube documentary titled Simply Complicated, which was released last October.
The New Mexico-born singer sparked concerns that she had suffered a relapse after releasing the song "Sober", which features the lyrics: "mommy, I'm so sorry I'm not sober anymore/And daddy, please forgive me for the drinks spilled on the floor" and ends with the lines: "I'm sorry that I'm hear again, I'm promise I'll get help/It wasn't my intention, I'm sorry to myself."
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