Jeremy Piven Jeremy Piven

Entourage star Jeremy Piven's decision to leave Broadway's Speed the Plow was on doctor's orders — and his internist says no one should make light of it.

"Jeremy has been a trooper doing the show as long as he did," Dr. Carlon Colker told "It was not his decision to step away from the show; it was my decision to end his run for health reasons.

Colker said Piven was diagnosed early in his run, which began in October, with a "profound elevated mercury level ... almost six times the upper limit of the reference range." The actor was hospitalized earlier this week for three days due to exacerbated symptoms from the condition. They included muscle weakness and dizziness.

Piven informed the producers that he hasn't been feeling well due to a high mercury count in his system.

"I talked to Jeremy on the phone, and he told me that he discovered that he had a very high level of mercury," David Mamet, who wrote the show-business satire, told Variety.

"So my understanding is that he is leaving show business to pursue a career as a thermometer."

Mercury poisoning is an extremely dangerous condition that can lead to muscle fatigue, kidney failure, cardiac arrest, psychiatric issues and death. Colker says Piven's treatment will include abstaining from all types of seafood and Chinese herbs, of which he was fond of taking. Piven will also undergo other "natural forms of detoxification."

Piven received mostly good reviews for the role. The New York Times' Ben Brantley said he performed "with uncanny grace and intelligence," and Variety's David Rooney said his "tightly wound physicality and easy command of rapid-fire, hectoring dialogue make him a natural fit for Mamet."

William H. Macy and Norbert Leo Butz have been tapped to replace Piven, with Tony winner Butz playing Piven's role Dec. 23-Jan. 11 and longtime Mamet pal and collaborator Macy stepping into the part for the remainder of the show, which ends Feb. 22.

What do you think about Piven's sudden exit from Speed the Plow?