Demi's family has not commented publicly on the developing situation.
Only four months ago, the singer attended a signing for her mother's new book, Falling With Wings, alongside Madison, and her 30-year-old sister Dallas Lovato. Around that time, Demi also commemorated six years of sobriety.
But a source recently told E! News that Lovato has been "heavily using" and stuck in a "downward spiral" over the past few months.
"She has had really good days where she is perfectly OK and on track and really bad days where her team and friends have been very concerned," explained the source. "She has distanced herself from many important people in her life and even let go of a few people on her team. Everyone has been urging her to get help with her life coach, and to seek treatment again, but Demi thought she could handle it on her own. Demi recently has wanted to be more social and out in about, and has been privately partying more with friends."
Through the ups and downs of Demi's sobriety journey, she has remained especially close to her little sister, who pop culture fans might remember from Desperate Housewives.
As Madison explained to Seventeen in 2015, "When Demi is home, our relationship is just like any sisters.' We get fro-yo and watch the ID channel—we're obsessed—and we talk about anything and everything. I know I can trust her with it all."
Demi also shared with the mag, "I tell Madison to call me as much as possible. I want her to come to me with things. I just let her know that I'm always there for her, whether I'm on the other side of the world or I'm next door."