Yes, Jared Leto did indeed lose weight for his role as Morbius in the upcoming Marvel movie.
He reportedly lost an astonishing amount of weight, dropping from a healthy weight of around 190 pounds to a shockingly thin 155 pounds. He also grew out his hair and beard, and his transformation was so extreme that some people didn't even recognize him.
It's clear that Jared Leto was committed to the role and willing to go to extreme lengths to make sure he looked the part.