The former Disney star took to Twitter late last night (14 March) to express her disappointment and anger at the 'Fame' singer.
Her comments came after Lady Gaga was vomited on (yuk!) as part of her act during a live performance earlier this week at South By Southwest festival in Texas.
Demi, who has admitted to suffering from bulimia in the past, believes Lady Gaga's performance of 'Swine' was not "cool" or "artsy" but an inappropriate reference to addiction.
'Skyscraper' singer and former X Factor judge Demi, 21, tweeted: "Sad... As if we didn't have enough people glamorizing eat disorders already. Bottom line, it's not 'cool' or 'artsy' at all.
"Would you let someone bring a needle and shoot up on you? Addiction is addiction.
"So it's cool if I do a speech about self-harm and then proceed to watch someone cut themselves on my stage?"
She also went on to insist she didn't "hate" Lady Gaga, and was still a 'little monster" herself - the name Lady Gaga calls her fans.
Demi then reached out to Lady Gaga directly, saying: "@ladygaga you're SO talented, if not one of the most talented in our industry PERIOD. Dope is INCREDIBLE.. but you don't have to do that (sic)".
Sad... As if we didn't have enough people glamorizing eat disorders already. Bottom line, it's not "cool" or "artsy" at all.— demetria lovato (@ddlovato) March 14, 2014
Lady Gaga has not yet responded to any of Demi's comments.
Demi had treatment for bulimia in 2010, while Lady Gaga herself has also spoken out about her own struggles with body image.
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