A woman accused of butchering, cooking and eating her two sons last week is believed to have done so because she hallucinated that they were pigs, Mental Health Department deputy director general Kiattiphum Wongrachit said on Tuesday.

“The woman killed her children because she didn’t continue her treatment and didn’t take her medication,” Dr Kiattiphum said.

He said mentally ill patients often became violent and experienced hallucinations if they stopped their regular treatment. About 90 per cent of violent cases involving mentally ill patients were due to lack of regular medication.

The woman, a member of the Musur hilltribe whose name was withheld, will be kept under close watch in the hospital for a long time, he said. The hospital will check whether she is a drug addict and if she will need to keep her calm when she realises that she killed her children, he said.

There are more than 600,000 patients being treated for mental illness by the hospitals under the Health Department, he said.

Police last week received a complaint that a Musur woman butchered her two sons, ages one and five years, in Chiang Mai’s Mae Ai district.

Police said they found her asleep at her home, with several body parts apparently from children near her.

They took her in for questioning, but she did not respond to any of their questions.

They did a background check on her and found that she had been treated for a mental illness in 2007.

She has been charged with murder, but being deemed mentally unfit to fight her case she was sent to Suan Prung Hospital for treatment.