The actress stumbled upon the whole Ozempic thing while speaking to The New York Times Magazine ... where she explained she's heard murmurings about "some pill that people are taking or something like that" ... but she didn't exactly know what it was.

Something to note here ... Ozempic, originally a type 2 diabetes drug, is used off-label in KW's native Britain, but it's not exactly all the rage there like it is here in the States.

As a result, Kate was apparently horrified when she found out what it's actually been used for ... with the star adding it sounded "terrible," and encouraging people to just eat more food instead.

Kate's disgust at the whole sneaky weight loss method makes total sense when you consider the public scrutiny she's faced about her body ... especially since her Titanic days back in '97.

She told the publication the historical comments about her weight got to the point where she began battling an eating disorder ... but she kept it to herself at the time.

Heartbreakingly, Kate shared that when she did lose weight, people would comment on how good she looked, reinforcing this idea that looking good was directly tied to how much she weighed.

Nowadays, when people try to comment on Kate's weight, she's not having any of it ... quick to call them out on it right then and there. Safe to say, Kate's been through the wringer on this issue ... so her feelings on Ozempic aren't all that surprising.