Demi Lovato turned back to alcohol and drugs after years of sober living made her "more miserable than when I was drinking".

The Confident hitmaker recently celebrated a year of sobriety following her near-fatal drug overdose in the summer of 2018, six years after previously kicking her substance abuse demons.

During an appearance on The Ellen DeGeneres Show, which will be broadcast on Thursday, the star explained the triggers for her relapse.

"I first got sober when I was 19, which was an age that I wasn't supposed to be drinking at all," she said. "I got the help I needed at the time and I took a 'one size fits all' approach and that was just sobriety."

While Demi added her approach worked for a long time, she later began to adopt extreme diets and intense workouts, which "led me to being really, really unhappy.

"I asked for help, but didn't get the help that I needed," she explained. "I was six years sober, but I was miserable. I was more miserable than when I was drinking."

Demi's comments come days after the Skyscraper star publicly addressed her relapse on social media, explaining how she "needed to make those mistakes".

"Today I would've had seven years sober. I don't regret going out because I needed to make those mistakes, but I must never forget that's exactly what they were: mistakes," she wrote in a post on Instagram. "If you've relapsed and are afraid to get help again, just know it's possible to that step towards recovery.

"If you're alive today, you can make it back. You're worth it," she added.

Demi made her musical comeback at the Grammy Awards in Los Angeles in January, when she delivered an emotional rendition of her track Anyone. Her new single I Love Me drops Friday.