The report said victims were released only when they vowed to drop their complaints.
Under a system dating from imperial days, Chinese people who suffer injustices can petition central authorities in Beijing for help.
The tradition has survived into the Communist era but has become a perilous undertaking for petitioners, who are often intercepted by local officials to prevent their complaints being aired in Beijing.
The abductions have been occurring in Xintai city in Shandong province since at least 2006, the report said, quoted an unnamed retired official who counted at least 18 such cases.
However, the head of the Xintai Mental Health Centre, Wu Yuzhu, was quoted admitting that the centre had "many" such petitioners in its care, paid for by the local government.
The report focused on the case of Sun Fashi, 57, who for years had sought compensation for himself and fellow villagers over land subsidence, caused by excessive coal mining, that damaged homes and farmlands.
Sun was abducted October 19 as he headed for Beijing to petition once again over the issue.
He was taken to the mental health centre, where he was frequently bound, drugged and threatened by staff and other patients when he demanded his release, the report said.
"The doctors said, 'We don't care if you are sick or not. If the government sent you, we are going to treat you,'" Sun was quoted saying. He was released November 12 after signing a pledge to cease petitioning.
Wu was quoted saying the centre had turned away many people brought by officials who were obviously healthy, but that the government often provided documents certifying they were mentally ill.