Kate Winslet's just found out about Ozempic, and let's just say she's not exactly jumping for joy about it -- making her thoughts known while munchin' on a pastry.

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. ...

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.