"This last year I experienced so much life and too much death," the singer, 22, wrote. "But I made it through… Sober. #4Years #GodsWill."
The former Disney star, who previously battled an eating disorder and drug addiction, entered rehab in 2012.
"I was dealing with bipolar depression and didn't know what was wrong with me," she said in an interview with HuffPost Live last May. "Little did I know, there was a chemical imbalance in my brain. Because I didn't tell people what I need, I ended up self-medicating and coping with very unhealthy behaviors."
Now back on top and happy with longtime boyfriend Wilmer Valderrama, Lovato credits the former That '70s Show star with helping her in her recovery.
"He never takes credit for my sobriety, but I guarantee I wouldn't be alive without him today," she said last year.
The "Confident" singer, who was heartbroken when her dog Buddy was killed by coyotes last year, was in a reflective mood as the anniversary of her sobriety approached.
"I can't believe I have four years," she wrote on Saturday, March 12. "Anything is possible."
I can't believe I have 4 years on Tuesday.. Anything is possible.— Demi Lovato (@ddlovato) March 13, 2016
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