Studies examining the link between the mother's use of antidepressant and antipsychotic medication during pregnancy and her child's odds of developing autism have thrown up a mixed bag of results. But the latest findings, published in the journal JAMA Psychiatry, suggest that (as with vaccines) there just isn't the evidence to support claims that these drugs pose a risk.

A multidisciplinary team of researchers at the Icahn School of Medicine at Mount Sinai studied the effect of more than 180 drugs on a sample of almost 100,000 children born anytime between 1997 and 2007. Each drug was sorted into one or more groups (of which there were 55 in total) depending on their biological target (rather than the condition that they were designed to treat), and a child was said to be exposed so long as their mother received a prescription for the medication during the pregnancy. 

By January 2016, 1,405 of those children had been diagnosed with autistic spectrum disorder (ASD), leaving 94,844 without a diagnosis to serve as controls. 

"When we assessed the effects of prenatal exposure to medications that affect major neurotransmitter systems, we found that the most of the associations are substantially modified when accounting for maternal characteristics [i.e. the disorder the medication was being taken to treat]," first author Magdalena Janecka, a postdoctoral fellow at The Seaver Center, said in a statement.

"What this suggests is that higher estimates of autism risk among offspring of mothers who take certain medications during pregnancy are most likely not due to pharmacological effects of those drugs." But, perhaps, the disorder those drugs are designed to treat.

When the researchers accounted for various factors including the child's year of birth, the mother's age at child's birth, her history of psychiatric and neurological disorders, and the number of medical diagnoses she received around pregnancy, they found very little to suggest that the medications themselves affected the chances of a child being diagnosed with ASD. 

What they did find, however, was a positive correlation between the number of diagnoses the mother received before and during the pregnancy and the likelihood her child would later be diagnosed with autism. This, they say, could cause confusion.

"In actuality, maternal number of diagnoses can confound associations between prenatal exposures and autism, and therefore should be accounted for in future studies," Janecka added.

So, what of those previous studies that have found an association? There were flaws in the design, the researchers say. Not only did they look at the autism risk in relation to just a small handful of drugs, but they also were not able to separate between the drugs themselves and the disorder they were supposed to treat.