Piven's abrupt departure from "Speed-the-Plow" was a move deserving of its own "Entourage" episode for all the rumblings it caused, but a statement by the show's producers lacked drama.
"We have been advised by Jeremy Piven's medical representatives that he is seriously ill and is unable to fulfill his contractual obligation to 'Speed-the-Plow.' Consequently, he has left the production 10 weeks early," the statement to ABCNews.com said.
According to the U.S. Environmental Protection Agency, the most common way people ingest mercury is by eating fish containing methylmercury -- most often tuna or swordfish -- or by breaking products containing elemental mercury, such as a thermometer.
Mercury is one of the most dangerous toxins on Earth. The amount of damage it can do to a person depends on when the person is exposed (as a fetus, child or adult), the type of exposure (whether it's swallowed, touched or inhaled) and the length of the exposure.
At its worst, inhaled mercury can cause brain damage or death. Swallowing mercury can cause permanent kidney damage or death. However, according to the University of Maryland Medical Center, most exposure to mercury builds up over periods of years. In that case, mercury poisoning can cause numbness, tremors, blindness and memory problems.
Mercury poisoning treatment can last for months and usually consists of extended use of "chealator" drugs which help remove heavy metals from the body, according to the University of Maryland Medical Center.
Two actors have filled in for Piven since his departure.
Tony Award winner Norbert Leo Butz took on the part in December and early January. Academy Award nominee William H. Macy took up the reins Tuesday.
In September, Piven picked up his third consecutive Emmy for his work on "Entourage" and, in his acceptance speech, alluded to the fact that small-screen acting talent doesn't necessarily translate to the stage, perhaps foreshadowing his abrupt departure from "Speed-the-Plow."
"I just got off a plane from New York in which I'm doing a play," Piven said. "And what's so interesting is that I'm in the midst of this rehearsal and I'm feeling like maybe I should go into roofing, I'm so bad. That's what it feels like right now."
The Associated Press contributed to this story. Additional reporting contributed by Lauren Cox.