Eventually, three generations down the line, the behavioral effects faded. But even at this juncture, cortisol remained low. “This is like your grandparents influencing your behavior, and your great-grandparents influencing your hormone levels,” explains study author Vance Trudeau, a neuroendocrinologist at the University of Ottawa.

It’s still unclear what these differences mean, but the fact that the changes were inherited from generation to generation at all might spark concern. While more work is needed, the researchers theorize this may be the result of epigenetics—a phenomenon in which chemical markers are added to DNA, altering the expression of genes without affecting the underlying sequence. In recent years, several studies have indicated that epigenetic modifications can be passed on to future generations, and this new study may be yet another example.

“We have to think about how we’re living our lives,” Vera-Chang says. “It’s not just us that are being affected by our actions.”

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About 10 percent of Americans, and over 16 percent of American women, currently use antidepressants. Fluoxetine, or Prozac, is an especially common selective serotonin reuptake inhibitor, or SSRI. Photo Credit: Tom Varco, Wikimedia Commons

However, researchers are quick to caution that it’s too early to jump to conclusions about human populations. Working with zebrafish makes it possible to conduct in-depth experiments that can’t be done in people—but analogs between the two species have their limits.

For one thing, humans who take antidepressants do so for a reason: to treat mental illness. All the fish in this study were healthy, making it tough to evaluate how a drug might traverse the barriers between a depressed mother and her child, explains Judith Homberg, a behavioral neurogeneticist at Radboud University in the Netherlands who did not participate in the research.

“We can replicate anxiety and depression to an extent in animal models,” explains Tim Oberlander, a developmental pediatrician at BC Children’s Hospital Research Institute in Canada who did not participate in the new research. “But ultimately, the human experience needs to be recognized as a unique thing.”

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Additionally, incubating fish eggs in a petri dish is only a partial proxy for the placenta, says Homberg. Placental function itself could be affected by fluoxetine, meaning there could be other, indirect effects on a human fetus.

Still, a Prozac bath may not be terribly far off the mark. The uterine environment isn’t the only source of indirect exposure to antidepressants: Fluoxetine is one of many chemicals that have been found in water surrounding urban centers. “The bioecological impact of this study is very important,” Kalueff, the Southwest University neuropharmacologist, explains. “This tells us what could happen to children who drink fluoxetine-enriched water in big cities.”

Unfortunately, we’re still waiting on some of the most critical, human-centric data. Prozac first hit the market in the 1980s; as such, we’re only about one-and-a-half generations into use, Trudeau explains. As things stand, there’s some evidence that children of mothers taking fluoxetine during pregnancy are more withdrawn or anxious, but there isn’t yet data on whether the effects persist into subsequent generations.

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A young zebrafish. While zebrafish don't physically resemble humans, the two species are very genetically similar, and both produce cortisol in response to stressful events. Photo Credit: Nikita Tsyba and Azamat Bashabayev, Wikimedia Commons

In the meantime, studies like these are essential for generating awareness, says Veerle Bergink, a psychiatrist and obstetrician-gynecologist at the Icahn School of Medicine at Mount Sinai who was not involved in the new find. “These findings show clearly that this is a topic that warrants further investigation in humans,” she adds. “We need to have these discussions. It’s a medical issue, but it’s also a societal issue.”

Ultimately, the researchers emphasize that results of this study aren’t prescriptive. While antidepressants may have their downsides, depression during pregnancy is also potentially damaging to a growing fetus. Women faced with this choice often find themselves saddled with a difficult decision—but every case is different. Concerned mothers-to-be should always engage in a careful risk and benefit evaluation with their physicians.

“There are many women who really need this medication to maintain mood stability,” Bergink advises. “For some women, it may be the best option to continue medication. However, there are also women for whom it may be a good option to see if they can taper, or seek alternate treatment, such as psychotherapy, cognitive behavioral therapy, mindfulness based therapy, or group support, among others.”

Oberlander agrees: There’s not going to be a one-size-fits all solution. “Is the treatment better or worse than the condition itself?” he says. “That’s the core question that we need to figure out urgently.”

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