A newly published study conducted in Denmark has suggested an association between attention-deficit/hyperactivity disorder (ADHD) and maternal use of acetaminophen (including Tylenol™) during pregnancy. It follows a US study done last year associating use of acetaminophen with development of autism and further confuses an already muddied understanding of just what causes ADHD, which affects up to 15 percent of all kids.
Denmark is famous in epidemiologic circles for its remarkable long-term studies of large populations followed for development of a wide array of conditions and diseases so it’s no wonder the investigator’s conclusions are causing serious pause. In this study, the Danish National Birth Cohort followed more than 64,000 kids several years after birth to determine who developed ADHD.
As part of the study, the Moms had provided information several times during and after the pregnancy regarding their consumption of acetaminophen. About half of the mothers reported use showing that its reputation as a “safe” drug has led to near runaway consumption. Using high-end statistical analysis, the researchers were able to demonstrate a small, but real increase in ADHD diagnoses by age seven among those whose mothers had consumed acetaminophen versus those whose mothers had not. More compellingly, the more and the earlier Mom took acetaminophen, the stronger the association.
All settled then, right? Nope—it’s not even close. There are countless other “causes” out there. Some are comparably compelling; others less so, including lead exposure, mercury exposure, too much sugar, food additives and other chemicals, too much TV, too many video games, head trauma, mean Moms, meaner Dads, and just about everything else.
And of course there is the gene, that hard-wired Calvinist gateway to gloomy fate. Some studies have found that, among identical twins, there is extremely high concordance for ADHD. If one twin has ADHD, the other has at least a 75 percent chance of receiving the diagnosis, too.
In an accompanying editorial to the Danish study, a group of Welsh psychologists and neurologists applauded the finding, but of course preached caution, too. An association, as we all know, is not the same as cause and effect. For example, people who wear blazers with ties are likelier than those who do not to develop prostate cancer. Women seldom wear blazers with ties and never develop prostate cancer—the strength of the association would be astounding. But surely no one would assume causality.
Which leaves us about where we started—in need of even more clear and less confounded studies of this extremely important public health problem. But these and so many studies like them sidestep the larger issue that looms any time people set out to find the cause of a potentially devastating problem: What is the effect of the news on the parents and families and children? How many mothers, exasperated by the day to day life of trying to support their child with ADHD went to bed calmly last night, but will sleep poorly this evening as the implicit blame—you took too much acetaminophen! IT’S YOUR FAULT!— seeps in. And behind the sleepless Moms will come binders full of freshly scrubbed lawyers looking to turn a buck on the news.
Epidemiologic research often fares very poorly when it leaves the lecture hall or dusty medical journal and finds the fast lane of public discourse. Subtleties of study design and interpretation are pulverized in the name of the sound bite of course, but this is old news. The far more disturbing aspect is the sneering tone of accusation that can creep into the latest revelation. Sure, when it boils down to too much alcohol or tobacco or cocaine, no one feels too bad about the news. But increasingly, as epidemiologic study dig deeper into ever-larger data sets, a disturbing surprise awaits investigator and public alike.
It is uncertain at best whether taking acetaminophen in any way “causes” ADHD and likely it will be years until the truth is known. But what is known is that, starting immediately, pregnant mothers everywhere will avoid acetaminophen as if it were poison, hoping to influence the fates a notch or two. Medicine, which has tried in the last decades to consider how best to disclose specific clinical information to a specific patient—the news, say, about the latest blood work— would do well to consider the deleterious impact on public sanity brought about by releasing preliminary studies connecting common exposures to medical conditions. In this instance, the casual link between half-baked information and parental angst would not be difficult to demonstrate.