Demi Lovato has spoken out on the recent death of Glee star Cory Monteith, who was found dead Saturday from a heroin and alcohol overdose. Lovato, who has also struggled with substance abuse, hopes that the actor's death will help raise awareness of the issue.Hollywood reacts to Cory Monteith's death"All it takes is one moment of vulnerability to get slipped into your addiction," she told People. "He didn't choose to die. It was the disease. It can creep up on you at any moment. It only takes one moment of relapse to potentially die. It's really scary, but I'm really hoping that from this, people are able to see this is a very, very, very dangerous disease."Lovato entered a treatment facility for "emotional and physical issues" in late 2010, but didn't open up about her substance abuse until more than a year later. "Promoters gave me drugs and alcohol in restaurants or clubs. They wanted me to come back so I would be seen there. ... Being a celebrity can be dangerous. Nobody says 'no.' That's why so many end up overdosing and dying. It could definitely have happened to me," Lovato said at the time.Watch Cory Monteith's final video message to a fan: "Stay out of trouble"Now that she's clean, Lovato, who turns 21 on Aug. 20, struggles with her addictions daily and makes sure not to create situations in which she'd be tempted to relapse, even if that means missing out on important milestones with her friends. "They can turn 21 and have their turn-21st-birthday," Lovato said. "I just don't put myself in those situations where I'm going to be at those 21st birthdays. I don't go to clubs. I just know it's something I can't do without being triggered. And that's OK."The X Factor judge added that she's "really, really broken" over Monteith's death and sends her sympathies to his girlfriend Lea Michele. "The main person in my thoughts is Lea," Lovato said. "I am praying for her so hard and I love her so much. I'm wishing her a lot of strength right now."