The Chinese action star known for his kung fu skills discussed his diagnosis during the taping of a talent show he's judging in China.
In Tuesday's taping, the 50-year-old Li appeared to have a fuller face and heavier frame.
He said his weight has fluctuated but he's taking it all in stride. Li joked about his weight gain and said "I'm fat, I don't have the time to lose it. It's a fact!"
He explained that exercise is not advised with the medication he's taking. An overactive thyroid, or hyperthyroidism, causes changes in a person's metabolism and heart rate, among other symptoms, but is generally treatable with medications.
Li was diagnosed in 2010. He kept his condition under control with medication, but it came back with a vengeance recently.
He said that he's tackling his illness head-on. "I'm just a regular guy, I'm not Wong Fei Hung, I'm not Huo Yuan Jia (kung fu heroes he portrays on film), I'm not a hero. I'm just like you."
A martial arts champion at a young age, Li turned to acting and began showing off his kung fu skills on big screens in the 1980s.
He catapulted to fame in the '90s with the "Once Upon a Time in China" films where he portrayed martial arts master Wong Fei Hung.
His Hollywood career includes such titles as "Lethal Weapon 4," ''Romeo Must Die" and more recently "The Expendables 2."
Li confessed there are times he's unsure if he's able to carry on with work, but he's determined. "I'm in pain, but I'm not suffering. I'm happy," he said.
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