In a study just published (1), pregnant rats fed SSRI drugs - which are usually prescribed for depression - gave birth to pups who exhibited similar behaviors to children with Autistic Spectrum Disorder (ASD).
The study in rats follows an epidemiologic study in humans, published in July 2011 in the Archives of General Psychiatry (2). That investigation found that children of mothers who took SSRIs during the year prior to giving birth were twice as likely to give birth to a child who developed autism.
Pups and Toddlers: Similarities
In a surprising similarity to humans, more of the male pups demonstrated ASD-like behaviors than female pups. In contrast with control-group rats who received no anti-depressant medications, the investigators found the pups whose mothers were given an anti-depressants were uninterested in play when young and displayed poor social behaviors as adults. They also showed abnormal responses to changes in their environment. For example, they froze at the sound of a novel tone and showed little interest in exploring new toys.
Other similarities between rat pups and children with ASD include a delay in parts of the brain processing sound, and abnormalities in the corpus callosum, a bundle of nerve fibers that allows both hemispheres of the brain to communicate with each other.
More people taking SSRI medications
The incidence of pregnant women taking SSRIs has grown from about 0.5 percent in 1985 when the first one came on the market to nearly 10 percent today, according to Ian Paul, one of the study's many authors.
Autism was initially described in 1943 and through the next decades the parameters expanded. In 1996, the rate of incidence was less than 1 in 1,000 births and by 2007 it reached about 1 in 200. The rates of incidence of ASD have roughly doubled every three-to-five years to 1 in 91 currently, Paul added.
The effect of genes
Michael Merzenich, another of the paper's authors said that a genetic component for autism risk is found in certain families, and is more strongly expressed in some members than in others.
"Genetic weakness can put a child at risk for autism origin," he said. "The neurological distortions attributable to SSRIs plausibly add to the child's neurological burdens. We think that SSRIs may thereby increase the risks of ASD. In any event, further study in child populations should determine if this is or is not the case. In this study we eliminated as many external factors as possible. But real-life situations are much more complex."
Even though I am not a fan of implying that the results of animal research apply to humans, there are some surprising similarities here, and it is known that SSRIs causes neurological damage in adult humans. The researchers are the first to admit that there are differences between the real life factors affecting rats and humans, and this research opens the door for more work into investigating whether there is an association between women taking SSRIs and them being more likely to give birth to children with ASD.
It would be unethical to conduct an experiment where mothers-to-be were deliberately given an SSRI medication to test the effects on their off-spring, and so science is left to best-guess using correlation. Correlation does not imply causality, and so researchers cannot conclusively say that SSRIs cause ASD in children. Since it would be unethical to test whether SSRIs lead to a lack of brain development and ASD in human children, pharmaceutical companies will, for now, remain somewhat protected from lawsuits. As more evidence gathers in the coming years, more people will join together to take legal action if the scales of correlational evidence tip in the direction of SSRIs and ASD being linked.
The reason people take SSRIs for depression is because their level of mental and emotional stress is affecting their ability to function on a daily basis. Mental and emotional stress, which is known to affect the neural development of a human fetus, could be an additional factor that leads to ASD in children. It could be the only factor affecting the onset of ASD, and the SSRIs could have no effect, or may even mitigate the effect of stress during pregnancy. More information has to be known before any conclusions can be made.
It is also possible that SSRIs cause ASD. The large rise in the number of diagnoses of ASD coincides with the rise in the number of people taking anti-depressants, and the lack of development in rat pups brains mirrors that found in humans. Sadly we are unlikely to know based on the limits of today's technology. What we can do is to reduce the need for anti-depressants by supporting each other by listening, showing each other love and gratitude, and finding healthy ways to cope with stress. Maybe we can reverse the trend?
What do you make of this new research?
Is it fair that pharmaceutical companies can be protected by the correlation does not imply causality rule?
What can we do as a society to reduce the number of people experiencing depression?
1 Simpson, K. L. et al. (2011). Perinatal antidepressant exposure alters cortical network function in rodents. Proceedings of the National Academy of Sciences. Published online October 24, 2011. Doi/10.1073/pnas.1109353108.
2 Croen, L. A., Grether, J. K., Yoshida, C. K., Odouli, R., & Hendrick, V. (2011). Antidepressant use durng pregnancy and childhood autism spectrum disorders. Archives of General Psychiatry, Published online July 4, 2011. Doi:10.1001/archgenpsychiatry.2011.73.
3. Eurekalert, October 24, 2011: http://www.eurekalert.org/pub_releases/2011-10/uoc--alt102411.php