【Hostess in Heat】

Demi Lovato says one word caused a radical shift in her life,Hostess in Heat forcing her to confront mental illness and substance abuse with determination and bravery.

This two-letter word, she says, had a life-changing impact: "No."

It's a word she wasn't used to hearing back in 2011, when she first entered CAST Centers for treatment to address substance abuse, self-harm, bipolar disorder and disordered eating. But when CAST co-creator Mike Bayer first told her that, no, she couldn't have her car keys to go out and get drugs, something clicked.

"I was living in a world where people would tell me yes over and over again because of the position I am in," she said. "For the first time, he told me no. That's how I knew that this was real and he genuinely cared about me."

The singer-songwriter and advocate opened up about her struggles, triumphs and passion for mental health advocacy on a panel Monday at the 2016 Social Good Summit in New York. Bayer also joined Lovato for the conversation, which was moderated by Today Showhost Hoda Kotb.

Lovato is now four-and-a-half years sober, and credits CAST with her continued sobriety. But it was a long road to get to stability for the superstar. When Bayer first met Demi Lovato, he described her as closed off, untrusting and unhappy. It's a stark contrast to the bubbly public personality Lovato has always embodied, making it almost hard to image the singer the person Bayer describes.

Lovato said the secret to her success in treatment was the tailored programs that addressed her specific needs. That method -- along with continued work on her herself -- has made it so she can now cope with the bad days and celebrate the good days.

"I do so much work on myself that some days I forget I'm bipolar," she said. "Other days, there are times where I have to buckle down and call people and check in with my therapist. I have to take my medication every single day ... Some days I think about drinking, and other days I don't. And that's what life is all about -- just focusing one day at a time.

"There are things I do every single day in order to not let it become a struggle every waking moment."

Earlier this month, Lovato announced she is now the co-owner of CAST, deepening her commitment to mental health advocacy.

The center is currently on the Honda Civic Future Now Tour with Lovato and Nick Jonas, where CAST Center representatives -- and, sometimes, the two singers -- speak about mental health issues and share personal experiences with audience members prior to the show. Over the course of the ongoing tour, Bayer said they have met with 10,000 people to get real about mental health in a low-pressure environment.

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"Having this platform helps us bring mental health mainstream and popular," Bayer said. "Physical health is something that is worked on in elementary school. Mental health isn't."

The motto of CAST Centers is "Freedom to be your best self." It's a phrase Lovato takes to heart, and she hopes to have an impact on those who struggle with mental health and substance abuse.

"My mom raised me to help others. It's as simple as that," Lovato said. "That's what I continue to do every single day of my life, is just try to create some sort of legacy so that when I'm gone one day, I will have made my mark on this planet and at least helped one person to be the best self that they could possibly be."

About Social Good Summit

The Social Good Summit is a two-day conference examining the impact of technology and new media on social good initiatives around the world. Held during U.N. Week on Sept. 18 and 19, the Social Good Summit unites a dynamic community of global leaders and grassroots activists to discuss solutions for the greatest challenges of our time. You can watch the event live at socialgoodsummit.com.

This year's summit is brought to you by Mashable, the United Nations Foundation, the United Nations Development Programme and the 92nd Street Y. For complete event details, visithttps://mashable.com/sgs.