CHICAGO – A government agency has dropped plans for a study of a controversial treatment for autism that critics had called an unethical experiment on children.

The National Institute of Mental Health said in a statement Wednesday that the study of the treatment – called chelation – has been abandoned. The agency decided the money would be better used testing other potential therapies for autism and related disorders, the statement said.

The study had been on hold because of safety concerns after another study published last year linked a drug used in the treatment to lasting brain problems in rats.

Chelation (kee-LAY'-shun) removes heavy metals from the body and is used to treat lead poisoning. Its use as an autism treatment is based on the fringe theory that mercury in vaccines triggers autism – a theory never proved and rejected by mainstream science. Mercury hasn't been in childhood vaccines since 2001, except for certain flu shots.

But many parents of autistic children are believers in the treatment, and NIMH agreed to test it.

The researchers had proposed recruiting 120 autistic children ages 4 to 10 and giving half a chelation drug and the other half a dummy pill. The 12-week test would measure before-and-after blood mercury levels and autism symptoms.

The study outline said that failing to find a difference between the two groups would counteract “anecdotal reports and widespread belief” that chelation works.

Autism is a spectrum of disorders that hamper a person's ability to communicate and interact with others. Most doctors believe there is no cure.

In canceling the study, the agency noted it would take another year to review the study and three years to do it. In the meantime, the agency said, it was likely that other research would “provide deeper understanding of the causes of autism and more refined avenues for developing treatments.”

Several scientists praised the decision, including the lead author of the rat study, which found lingering problems in animals that did not have elevated lead levels.

“I think they're making the right decision not to go forward with the study,” said Barbara Strupp, a professor of psychology and nutritional sciences at Cornell University.

“Our data raise concerns about administering (the chelation compound) to children who do not have elevated levels of heavy metals,” Strupp said.

Dr. Paul Offit, chief of infectious diseases at the Children's Hospital of Philadelphia, agreed with the decision to cancel.

“Suppose that a child suffers a severe side effect from chelation,” said Offit, author of “Autism's False Prophets,” a new book on autism research. “Without any evidence it's helpful, I think it's unethical.”

The chelation drug proposed for the study, DMSA, can cause side effects including rashes and low white blood cell count.

“This was a wise and careful decision,” said Ellen Silbergeld of Johns Hopkins University's Bloomberg School of Public Health, who had been invited to comment on the study during an earlier review, in an e-mail.

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