I'd doubt he has in the last 6-8 years. International competitions actually do real testing, and NBA players on national teams are not remotely exempt from them. Before then, maybe? I mean, juicing is so nebulously defined, and there are a multitude of OTC supplements that could be considered juicing today that would not have been at the time of their availability 8-10 years ago. For example, when he was in high school, he could have walked into his local GNC and picked up androstenedione off the shelf. Even though it had been banned in the NBA since 2000, it wasn't declared an anabolic steroid until 2005 by the FDA. If he did, would you count that as juicing?
Anyway, I don't think he uses any drug or hormone currently restricted or banned by the NBA. He's a big dude, but college football coaches recruited him as a tight end, so people always thought his body would fill out like it has. He's stayed remarkably healthy, but some guys just get lucky. Jordan did. Part of being transcendently great is staying healthy enough to maximize your abilities. There's definite luck to it. And maybe playing all those games in his 20s will catch up to him in his 30s, but he's ridiculously good at basketball, so I see him adapting as his physical superiority starts to decline.
As for the weight loss, the last two years in Miami he played 82% of his minutes at the power forward position. This year he was joining a team with Kevin Love and Tristan Thompson, so obviously he's going to play the majority of his minutes at the 3. I don't think we have to go down the conspiracy theory route to imagine he might want to train his body more for the speed and agility required of a wing than the strength required of a power forward. The guy has 24/7 access to dietitians/nutritionists, personal chefs, and personal trainers. I'm fairly sure he could drop 20 pounds to focus on improving his agility.