Mehdi Mahmoudian, a journalist and member of the Society for the Defense of Prisoners' Rights, was arrested in September 2009 by Intelligence Ministry forces.
His mother, Fatemeh Alvandi, told Radio Farda on May 31 that one of her son's lungs has almost collapsed due to what she called the torture that he has been subjected to.
But Alvandi said her son is determined to continue the hunger strike despite the deterioration in his health.
Mahmoudian has gone on several hunger strikes in recent months.
Mahmoudian is being held at the Rajaee Shahr prison in Karaj, west of Tehran.
He was placed in solitary confinement after he wrote an open letter to Supreme Leader Ayatollah Ali Khamenei that provided alleged details of widespread rape in the prison.
"Once when he was being interrogated, he received two strong penicillin shots at the same time, as a result of which he had a seizure," Alvandi said.
She added that her son has had occasional seizures ever since that time, and prison doctors say he has developed epilepsy.
Listen to more in Persian here