Miley Cyrus to Justin Bieber Fans -- DON'T CUT YOURSELVES ... It's Not Funny

Miley Cyrus is trying to put a stop to a new sick trend that's emerged on the Internet -- a trend that involves self-described Justin Bieber fans mutilating their bodies after seeing the pics of the singer smoking pot.

The hashtag #cut4bieber has become the top U.S. trend on Twitter ... after people began posting photos featuring bleeding arms, allegedly the result of "cutting" by disappointed fans looking to pressure the singer into giving up his pot habit.

In fact, someone even started a website encouraging Bieber fans to cut themselves and post photos of the carnage .... until Bieber gives up marijuana for good.

But moments ago, Miley Cyrus weighed in on the troubling trend -- retweeting a messaging saying:

"#cut4bieber? Cutting is NOT something to joke about. There are people who are actually suffering from self-harm, this is so disrespectful."