Antidepressants and Autism

The incidence of autism in children has increased enormously over the past generation. The following plot provides the growth of reported cases per thousand children.

There is some question about the fraction of these cases that are derived from greater awareness and more accurate diagnoses, but most would agree that the occurrence is growing alarmingly. No precise cause is known, but most discussions include both genetic and environmental factors. A few recent studies have highlighted environmental effects. One is of particular interest because it identifies a specific risk factor.

A study be a Kaiser Permanente group on a collection of children indicated that the incidence of autism was significantly increased when mothers took antidepressant medications during pregnancy or within the year before birth. Specifically, they referred to selective serotonin reuptake inhibitors, the class that contains most of the common antidepressants.

"....we found a 2-fold increased risk of ASD [Autism Spectrum Disorders] associated with treatment with selective serotonin reuptake inhibitors by the mother during the year before delivery (adjusted odds ratio, 2.2 [95% confidence interval, 1.2-4.3]), with the strongest effect associated with treatment during the first trimester (adjusted odds ratio, 3.8 [95% confidence interval, 1.8-7.8]). No increase in risk was found for mothers with a history of mental health treatment in the absence of prenatal exposure to selective serotonin reuptake inhibitors."

In other words, taking this class of medication during the first three months of pregnancy leads to between 1.8 and 7.8 times increase in probability of producing an autistic child, with the most likely enhancement being 3.8 times. During the first trimester the fetus is busy constructing its brain and wiring its nervous system, it seems obvious that would be the time that it is most vulnerable to some form of chemical assault.

The authors of the study refer to their results as a modest effect. I find them frightening. The data provided above is approaching a one percent probability that a child born will suffer some level of autism. Now you find a common medication that, if taken during pregnancy, could make the risk from 2-8 times greater. Those are beginning to look like odds one might not want to bet against.

The Kaiser study has identified a risk factor, but there is no mechanism specified. How many molecules of this class of drug does it take to alter the development of a fetus? One? Trillions?

We discussed here the issue of pharmaceuticals and other drugs building up in our water supplies. There is a reference in Discover Magazine to a study performed to test the effect that observed levels of antidepressants might have on small fish

"Chemists have found that water downstream of water treatment plants holds a veritable medicine cabinet worth of antidepressants, including venlafaxine, bupropion (Wellbutrin), citalopram (Celexa), fluoxetine (Prozac) and sertraline (Zoloft)."

"The concentrations of antidepressants in the water—billionths of a gram per liter—aren’t enough to affect larger species, but they are enough to make small fish and fish babies feel woozy. Researcher Meghan McGee tested the effect of antidepressants on young minnows by exposing unhatched and newly-hatched minnows to levels of antidepressants commonly found downstream of water treatment plants. The drugged minnows appeared lethargic and took twice as long to react to stimulus, making them much more vulnerable to predators."

Remember that downstream from water treatment plants are often other towns that use the river as their water supply. Most treatment methods are not effective at eliminating these types of chemicals, so the problem gets passed on, and, to the degree that processed water gets recycled into the drinking water source, the chemicals can build up.

If the background level of antidepressants in rivers can be great enough to affect the performance of small fish, I think it is appropriate to re-ask the question: how many molecules does it take to affect a fetus less than three months in development? It may be time to start worrying more about what we are drinking.