Why These Salmon Are On Anxiety Meds

A fish walks into a pharmacy ... well, not exactly. Fish aren't being prescribed anti-anxiety drugs. But they are experiencing the effects. Researchers have found more than 900 different pharmaceutical ingredients in rivers and streams around the world, though they're not yet sure how this could change the behavior of fish and other aquatic animals in the wild. "We can't, you know, dump a bunch of pharmaceuticals into the river," says Jack Brand https://www.slu.se/cv/jack-brand/, biologist at the Swedish University of Agricultural Sciences. Instead, Jack's team did the next best thing – with some surprising results. This episode was reported by NPR science correspondent Jon Lambert https://www.npr.org/people/703751120/jonathan-lambert. Check out https://www.npr.org/2025/04/14/nx-s1-5359433/anxiety-drugs-found-in-rivers-make-salmon-take-more-risks more of his reporting. Want to hear more stories about animal behavior? Email us and let us know at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ atplus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:19Emily Kwong?

  You're listening to Short Wave from NPR.

• 0:24Emily Kwong?

  Hey, Short Wavers. Emily Kwong here. And today I am joined by NPR science reporter Jonathan Lambert. Hey, John.

• 0:30Speaker 02

  Hey, Emily.

• 0:31Emily Kwong?

  John, I must thank you for all the hilarious and fascinating science stories you've been bringing us lately. Like chimps contagiously peeing, or iguanas sailing the high seas. Or this most recent banger, salmon on drugs. What's that about?

• 0:47Speaker 02

  Yeah, salmon on drugs, specifically anti-anxiety drugs.

• 0:52Emily Kwong?

  How are salmon getting a hold of, not that they have hands, but how are they getting a hold of anti-anxiety pills?

• 0:58Speaker 02

  Basically through us. So when humans take medication, like for anxiety or bacterial infections, our bodies don't use all of it, and we end up peeing out some of the chemicals. That can end up in wastewater, which can get into rivers and streams. And runoff from pharmaceutical factories gets into waterways, too. All told, researchers have found more than 900 different pharmaceutical ingredients in waterways around the world.

• 1:23Emily Kwong?

  900 different ingredients? That's a lot.

• 1:27Speaker 02

  Yeah.

• 1:27Emily Kwong?

  Well, how does this then affect the fish and other aquatic creatures?

• 1:31Speaker 02

  We're not entirely sure. Scientists have been trying to figure out what all this pollution could be doing to fish, and most of that has been done in the lab. Those experiments have shown that giving fish anxiety meds, for instance, kind of messes with their behavior.

• 1:45Emily Kwong?

  How so? Like, when researchers give fish medicine on purpose, what happens?

• 1:49Speaker 02

  Yeah, so if researchers give fish, say, a benzodiazepine, like Xanax, or an SSRI, like sertraline, in the lab, these fish become more antisocial and more prone to take risks. But it's hard to say how these drugs affect their behavior out in the wild.

• 2:05Speaker 03

  We can't, you know, dump a bunch of pharmaceuticals into the river.

• 2:10Speaker 02

  That's Jack Brand. He's a biologist at the Swedish University of Agricultural Sciences, and he worked on a study that kind of did the next best thing from a scientific perspective.

• 2:20Emily Kwong?

  OK.

• 2:21Speaker 02

  The study was published in the journal Science this past month. The team implanted pharmaceuticals in Atlantic salmon in Sweden and monitored how two drugs, an anxiety med and a pain med, influenced their migration behavior.

• 2:34Emily Kwong?

  I'm so curious. What happened?

• 2:37Speaker 02

  Something kind of unexpected. The anxiety medication actually improved the migration success of the salmon.

• 2:44Emily Kwong?

  Wait, so the drugs helped?

• 2:46Speaker 02

  In this narrow sense, yeah, they did seem to help. But that's not the whole story.

• 2:53Emily Kwong?

  OK, so today on the show, how scientists managed to drug salmon in the wild, what pharmaceutical pollution could be doing to aquatic animals worldwide.

• 3:02Speaker 02

  And what we can do about it.

• 3:04Emily Kwong?

  You're listening to Short Wave, the science podcast from NPR.

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• 4:32Emily Kwong?

  Okay, John, so let's back up a second. Because pharmaceutical drugs are designed to work on human brains and bodies, right? So how do they end up affecting the brains and bodies of fish?

• 4:42Speaker 02

  Yeah, so it turns out a lot of drugs that act on our minds target parts of the brain that have a deep evolutionary history, and so they're shared by lots of different animals.

• 4:50Emily Kwong?

  Mm, okay.

• 4:51Speaker 02

  So they can work on salmon in similar ways that work on humans. Now, it's not like fish are literally popping pills like we would. What's happening is the pills are getting super diluted in rivers and entering their bodies through their gills.

• 5:04Emily Kwong?

  Oh, huh.

• 5:06Speaker 02

  Yeah. But even with super-low concentrations, like what a fish would encounter in the wild, these drugs are still altering their behavior in the lab.

• 5:15Emily Kwong?

  This all makes sense. It sounds like a big problem, so there have been a lot of experiments to understand the problem on a deeper level, but way fewer field experiments. So how are researchers studying the effects of drug exposure in the wild?

• 5:30Speaker 02

  So researchers put these, like, slow-release capsules into the bodies of over 250 juvenile hatchery-raised Atlantic salmon. The capsules released two drugs: a benzodiazepine called clobozam, used to treat anxiety, and an opioid used for pain management called tramadol.

• 5:49Emily Kwong?

  So why these two drugs, clobozam and tramadol in particular?

• 5:53Speaker 02

  In humans, these drugs can cause harmful interactions, and so the researchers wanted to see if combining them had, like, extra bad effects.

• 6:02Emily Kwong?

  Yikes, okay.

• 6:03Speaker 02

  They're also found in lots of rivers around the world, but not in the river where these particular salmon live.

• 6:09Emily Kwong?

  Okay, so this sounds like a very good river in which to conduct this study.

• 6:12Speaker 02

  Yeah, yeah, exactly. Overall, they had four different treatments: no drug, only clobozam, only tramadol, and both.

• 6:20Emily Kwong?

  Okay, well, what did they do next?

• 6:22Speaker 02

  They also implanted these tracking devices, so the scientists could follow the fish as they migrated from a release site in a Swedish river out to the Baltic Sea.

• 6:31Emily Kwong?

  So they put, like, GPS on the fish?

• 6:34Speaker 02

  Not exactly. They were like little devices that emit a sound. And then the researchers placed a bunch of receivers along the migratory route that pick up that sound, allowing them to kind of like reconstruct the journey.

• 6:46Emily Kwong?

  Oh, so it's like air tags for salmon.

• 6:49Speaker 02

  Yeah.

• 6:49Emily Kwong?

  All right, so they have this, these experimental conditions. They have the salmon trackers. What did they find?

• 6:56Speaker 02

  It was a bit of a surprise. So one drug, the pain medication, didn't seem to make any difference. But it turned out that fish exposed to Clobosam were actually more successful in reaching the Baltic Sea than salmon who weren't exposed.

• 7:11Emily Kwong?

  Interesting. Let's break this down a little bit. Why would an anti-anxiety drug like Clobosam make fish better at migrating?

• 7:19Speaker 02

  Yeah, the researchers aren't 100% sure, but one part of their results hinted an answer. So this route, this migration route, is not exactly like a lazy river. There are two hydropower dams, each with a series of turbines that the fish have to cross to get to their destination. Those can be pretty hairy. Here's Olivia Simons, a salmon biologist at the Norwegian Institute for Nature Research.

• 7:44Speaker 05

  Basically, with turbine passage, you can get injuries, which are of course not good if you have a long way to swim. And you also get mortality. So if they're struck by a blade, they can die. So that's not good.

• 7:56Emily Kwong?

  It's tough out here being a salmon.

• 7:59Speaker 02

  Yeah. So non-drugged fish really took their time navigating these dams. Like, I imagine them waiting together in a group and going, oh, not yet. Wait, wait. Okay. But the Clobosam-exposed fish did it 2 and 1/2 to 3 times faster.

• 8:16Emily Kwong?

  Those drugged fish were like, I'm ready.

• 8:18Speaker 02

  Yeah, yeah. Here's how Brand explained it.

• 8:21Speaker 03

  So we actually found that more Clobosam-exposed fish eventually migrated through the river and reached the Baltic Sea, their destination, more than unexposed fish.

• 8:33Emily Kwong?

  Poor salmon friends. So the anti-anxiety meds made those salmon, you know, I guess, migration risk takers, but it left those unmedicated salmon behind.

• 8:44Speaker 02

  Yeah, on the face of it, it kind of seems like this study is basically saying that it's good to give salmon benzos, but the authors caution against that interpretation.

• 8:54Emily Kwong?

  Yeah, I imagine that taking more risks might help fish reach the Baltic Sea faster, but it could pose problems once they get there.

• 9:03Speaker 02

  Exactly. A follow-up lab experiment they did found that cloiazam made salmon less likely to shoal with other salmon. Shoaling is when fish group together for a safety in numbers kind of thing, and setting off on your own could make it easier for ocean predators to pick you off.

• 9:18Emily Kwong?

  Yeah, lone wolf, lone salmon behavior.

• 9:21Speaker 02

  Yeah, cloiazam essentially made them more antisocial and willing to live a bit more dangerously. Scaled up, a lot more antisocial and risk-prone salmon could ultimately shrink the population.

• 9:33Emily Kwong?

  Yeah.

• 9:34Speaker 02

  And that could cause problems for the whole ecosystem.

• 9:37Emily Kwong?

  Mm-hmm. Now, John, migration is just one part of the Atlantic salmon's life cycle, right? So how else did the drugs affect them?

• 9:46Speaker 02

  Yeah, so it's honestly a little bit of a limitation of this study in that it's just looking at this kind of narrow slice of an animal's life. Showing that drugs can influence behavior in the wild was still a huge accomplishment, but there are still a lot of unknowns.

• 10:00Emily Kwong?

  Right. Cloiazam is just one drug, but you said earlier that over 900 different pharmaceutical ingredients have been found in rivers and streams worldwide.

• 10:09Speaker 02

  Yeah, exactly. Here's what Karen Kidd, an ecotoxicologist at McMaster University, had to say.

• 10:15Speaker 06

  You think of the soup of pharmaceuticals that are going into our rivers, you know, that's a huge unknown. We have no idea what those anti-anxiety medications, plus the analgesics, plus the antibiotics, you know, plus the antiepileptics, plus the chemotherapids, et cetera, et cetera, collectively are doing to fish and other aquatic species.

• 10:41Emily Kwong?

  Yeah, absolutely. So is there anything we can do as consumers, or just as a society, about pharmaceutical pollution that doesn't, you know, require people to stop taking drugs that make their lives better?

• 10:53Speaker 02

  Yeah, there definitely are things we can do. One way is by designing wastewater treatment plants that do a better job filtering out drugs. A study from a few years ago actually found that pharmaceutical pollution in rivers is often worse in low-to-middle-income countries because wastewater management infrastructure there doesn't catch it all.

• 11:11Emily Kwong?

  Interesting. Okay, so better filtration systems. What else, John?

• 11:15Speaker 02

  There's also a push to design greener drugs, basically tweaking pharmaceuticals to degrade more easily in the environment, but still be just as effective in humans.

• 11:26Emily Kwong?

  That's so interesting because, right, there's like greener cleaning products out there, greener makeup products. Greener medicine could totally be a thing.

• 11:35Speaker 02

  Yeah, yeah. And these solutions aren't silver bullets, but they could lessen our impact. And with climate change and habitat destruction already majorly disrupting animal lives, it's important to try to do what we can to ensure our waste isn't disrupting their behavior, too.

• 11:51Emily Kwong?

  John Lambert, another incredible science story. Please come back any time. Thank you so much.

• 11:57Speaker 02

  Thank you.

• 12:01Emily Kwong?

  This episode was produced by Hannah Chin and edited by me, Emily Kwong and Rebecca Ramirez. Tyler Jones checked the facts. Kwesi Lee was the audio engineer. Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Emily Kwong.

• 12:18Speaker 02

  And I'm Jonathan Lambert.

• 12:19Emily Kwong?

  Thank you for listening to Short Wave, the science podcast from NPR.

• 12:29Speaker 00

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