The "Neon Lights" singer took to Twitter to vent her frustrations about the shocking incident, saying that Mother Monster glorified bulimia.
"Sad… As if we didn't have enough people glamorizing eating disorders already. Bottom line, it's not 'cool' or 'artsy' at all," she wrote.
But Lovato's war of words against the pop star didn't end there.
She added, "Would you let someone bring a needle and shoot up on you? Addiction is addiction."
The Lovatics are known for being a rather zealous group of fans, just as Gaga's Little Monsters, so it was only a matter of time before tweeters retaliated by attacking the former Disney darling.
But Lovato, who's never been afraid of speaking her mind, fought back to the haters.
"It's not 'shade' and it's not 'hate,'" she explained.
"But if someone has to come forward and say it…I'll take the heat for it. Putting the word ART in it isn't a free card to do whatever you want without consequences."
She then tweeted directly to Gaga and said, "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."
During today's keynote speech at SXSW, Gaga herself shared how the now infamous vomiting act came about.
"I've known Millie [Brown] for I think like five years now and we've actually collaborated before…she was just in town and so we thought we would collaborate again," she told the audience.
"It was just exciting to see people talk about performance art on the internet. We really just did it because we believe in the performance and we believe in what it meant to the song."
However, even Gaga knew that she had pushed the envelope far. During her sit-down chat, she admitted that she was worried her team wouldn't approve of her latest onstage antics.
"I asked my publicist if she quit in the middle of the show!" she said while laughing.