The 25-year-old singer shared a note on Instagram on Sunday.
"I have always been transparent about my journey with addiction," Lovato wrote. "What I've learned is that this illness is not something that disappears or fades with time. It is something I must continue to overcome and have not done yet."
"I want to thank God for keeping me alive and well... I now need time to heal and focus on my sobriety and road to recovery," she continued. "The love you have all shown me will never be forgotten and I look forward to the day where I can say I came out on the other side. I will keep fighting."
A source told ET last week that the singer is "doing much better" and is expected to leave the Cedars-Sinai Medical Center in Los Angeles soon.
"Her and her team need to decide what is the best decision for Demi once she leaves the hospital," the source said, referencing reports that her family wants to get her back into rehab immediately. "Demi has told the people close to her that she is serious about her sobriety, and plans to do whatever it takes to maintain a healthy lifestyle moving forward."