New research is questioning the effectiveness and safety of a controversial autism therapy.

The approach called chelation is designed to remove heavy metals from the body. While popular in some circles as a method to treat autism, chelation has been widely criticized as well.

Now, in a new review of existing studies on the practice, researchers say that chelation is not only unproven, but may also be unsafe.

“Chelation therapy represents the ‘cart before the horse’ scenario where the hypothesis supporting the use of chelation was not validated prior to using it as a form of treatment,” said Tonya Davis of Baylor University who co-authored the analysis published in next month’s issue of the journal Research in Autism Spectrum Disorders. “Evidence does not support the hypothesis that ASD symptoms are associated with specific levels of metals in the body.”

For the review, Davis and her colleagues analyzed five published studies looking at 82 people ages 3 to 14 who received chelation treatment. Despite mixed or positive findings in all of the studies reviewed, the research team found methodological flaws throughout the existing science. In many cases, for example, study participants were trying several treatments in addition to chelation making it unclear what attributed to any success they experienced.

Meanwhile, the review notes that side effects of chelation include fever, vomiting and hypertension. There is also a risk of cardiac arrest with the treatment.

“While I understand a parent’s desire to try anything and everything that may help their child, as a researcher, it is difficult to watch a family spend time, money and resources on interventions that research has found to be ineffective, or worse, potentially dangerous,” Davis said.