The National Institute of Mental Health (NIHM) has called off the proposed study to examine a controversial type of treatment for autism voicing doubts about the procedure’s safety. The treatment called chelation is a therapy in which a man made amino acid called EDTA is added to the blood and it is used to treat heavy metal poisoning. This has been used as a form of alternative medical treatment for children with autism.

A theory rejected by most scientists but advocated by autism activists, is that autism is caused by exposure to mercury, a heavy metal. They feel this exposure is caused by the childhood vaccines that are given to children in routine. The U.S. Centers for Disease Control and Prevention have said that mercury containing preservatives have not been used in childhood vaccines with the exception of certain influenza vaccines since 2001.

A study published last year said there was a link between EDTA and lasting brain problems in rats which led the government to cancel the proposed study that was given initial permission in 2006.

"NIMH has decided that resources are better directed at this time to testing other potential therapies for autism spectrum disorders, and is not pursuing the additional review required to begin the study," said the institute which is a part of the U.S. National Institutes of Health.

The statement added that, "No subjects were recruited for this clinical trial. In February 2007, based on new scientific data, an NIH Institutional Review Board reassessed the risk-benefit ratio of the proposed study. The board determined that there was no clear evidence for direct benefit to the children who would participate in the chelation trial and that the study presents more than a minimal risk," it said.

The institute said it plans on using the money for the canceled study to test other therapies for autism and other such disorders.