Superstar MEL GIBSON is sud­denly looking like a muscle-bound bodybuilder – and medical experts believe he has resorted to steroids, hu­man growth hormone or both to bulk up quickly for his role in Sylvester Stal­lone’s “The Expendables 3.”

The hunk-turned-hulk was recently pap snapped at the Beverly Hills Rejuvenation Center, which specializes in controversial, prescription-only hormone replacement injections.

Hollywood’s most infamous hothead allegedly exploded at Malibu cops recently, and medi­cal experts who haven’t treated Gibson say the 57-year-old actor’s behavior is consistent with “roid rage,” which can be induced by taking hormones.

The experts add that it’s un­likely such a dramatic change in Gibson’s physique could be ac­complished without steroids or human growth hormone.

“The recent growth in Mel Gibson’s muscle size is incredible and so spectacular that if he is do­ing this with just lifting weights, he is able to grow muscle better than just about everyone else,” declared Dr. Gabe Mirkin, a re­tired sports medicine specialist who has not treated Gibson.

On Sept. 6, the “Braveheart” star was spotted leaving the Beverly Hills Rejuvenation Center with its co-owner Dan Holtz, a major advocate of human growth hormone.

Gibson’s representative denied he is taking steroids or HGH, insisting that he uses only vitamins and supplements and has been eating well and working out with a trainer. But shocking evidence – includ­ing Mel’s recent, out-of-control encounter with Malibu cops – indicates that might not be the case, suggest experts.

On Aug. 31, Mel – who is di­vorced with eight kids – and a female companion were stopped at 1 a.m. at a drunk-driving check­point on Pacific Coast Highway.

Officers say Gibson was asked for his license and was pulled over for a secondary screening when he said he didn’t have it.

The “Mad Max” actor reportedly blew up and demanded to know: “Why are you harassing me?” He then added: “I have had problems with you deputies in the past.”

Indeed, deputies from the same law enforcement office busted Gibson for drunk driving in 2006, sparking his infamous expletive-laced, anti-Semitic rant.

His reaction comes as no surprise to renowned New York clinical psy­chologist Dr. Judy Kuriansky, who has not treated Gibson but noted: “Taking steroids or hormones can definitely increase aggression in men who are predisposed to vio­lence and angry behavior.”

And Los Angeles-based addic­tion expert Dr. Gregory Smith, who has extensive experience with HGH but has not treated Gibson, told The ENQUIRER it can have an effect similar to steroids in cer­tain individuals.

“HGH does restore youthful strength. And someone like Mel, who has always been hotheaded, may be more likely to express aggression with his newfound youth.”