"Quite often a voice is telling them to jump off a bridge or run under a train," he said.
Leff and his colleagues had difficulty recruiting enough people for the 55,000-pound pilot study because he said other doctors were reluctant to refer patients for an unproven treatment. Only 16 of the 26 participants completed the trial, he said. Some were deterred by voices they heard threatening to harm them if they participated.
"The voices, which can be terribly brutal, end up saying to patients, 'if you try this therapy, I'm going to kill you'," Leff said.
The therapy isn't the answer for everyone with schizophrenia, Leff said. Those who heard more than one voice had difficulty concentrating when other voices interrupted. Some patients enjoy their auditory hallucinations, such as a young man Leff didn't treat in the trial because the voice he heard was of a broadcaster commenting on his favorite soccer team.
The Wellcome Trust is interested in the research because mental illnesses such as schizophrenia and depression remain a significant health burden, said John Williams, head of neuroscience and mental health at the charity.
"One of our major challenges is understanding the brain," Williams said.
The pilot study was funded by the National Institute of Health Research and Camden and Islington NHS Foundation Trust. The trial funded by Wellcome will enroll as many as 140 patients at least 18 years old at centers in Britain, Vienna and Bologna, Italy. It will primarily measure the reduction in stress from voices, Craig said.