Is Justin Bieber Taking Steroids?

Justin Bieber's new bulked-up body has some people asking if he's taking steroids. INSIDE EDITION has the scoop.

Justin Bieber—Incredible Hulk? 

This photo just posted by the teen idol shows him with bulging muscles. Now, people are wondering how he got so big so fast.

One celebrity gossip site asks straight out: "Is Justin Beiber using anabolic steriods?"

You can see the dramatic difference. Justin has gone from not so toned, to bulked-up muscle.

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Dr. Raskin told INSIDE EDITION, "To me, as a medical expert, when I see that amount of size on someone with that amount of definition in a quick period of time, steroids are the first thing that I think about."

But Dr. Raskin says it's definitely possible to look like Bieber without any performance enhancement drugs.

"It can be done with the proper amount of training and the proper diet, but it might take quite a bit longer," said Dr. Raskin.

Bieber's personal trainer insists it was done the natural way. He says he works out with Bieber five days a week, and because Bieber is so active and young, he can eat whatever he wants, even fast foods.

The trainer says the goal is for Bieber to look like Mark Wahlberg from his days as an underwear model.

Even Miley Cyrus, of all people is telling Bieber it might be time to slow it down. She recently told Rolling Stone magazine, "You don't want to become a joke. Don't come in shirtless."