An antioxidant supplement that’s readily available at drugstores may be able to significantly reduce irritability and some behaviors in those with autism, new research suggests.

In a small study looking at 31 children with autism ages 3 to 12, researchers found that when the kids took a supplement known as N-Acetylcysteine, or NAC, they exhibited less irritability and fewer repetitive behaviors.

Though the finding is preliminary, researchers behind the study said that it is significant because the supplement has far fewer side effects than the second-generation antipsychotics often used today to treat irritability in kids with autism. What’s more, they said it could be the first drug to address repetitive behaviors like hand flapping.

For the study, some children were given NAC while others received a placebo for 12 weeks. Participants were assessed every four weeks to measure changes in behavior, socialization and other trends.

When tested using a standardized assessment for irritability, researchers found that scores for those taking NAC decreased significantly from 13.1 to 7.2, representing an improvement, according to the study published Friday in the journal Biological Psychiatry.

Repetitive and stereotyped behaviors also decreased in kids taking the supplement, the study found.

The drop in irritability is not quite as significant as the results currently seen from antipsychotic medications. “But this is still a potentially valuable tool to have before jumping on these big guns,” said Antonio Hardan of the Stanford University School of Medicine who led the study.

Despite the positive results, Hardan and his colleagues cautioned that the findings would first need to be verified in a larger trial before the supplement could be recommended for use in those with autism.

Currently, NAC is available as a dietary supplement at groceries and drugstores, but the over-the-counter variety varies somewhat from the pharmaceutical-grade product used in the study and may not produce the same results, researchers said.

“When you open the bottle from the drugstore and expose the pills to air and sunlight, it gets oxidized and becomes less effective,” Hardan said.

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