This is no longer a purely theoretical question, thanks to the modern world. Giving a liberal dose of cocaine to an eel turns out to be far worse for the eel than it is for us.

One study exposed silver eels, a common European eel that has recently dropped in numbers, to cocaine for about fifty days. Fifty days’ worth of cocaine would cause problems for anyone. Scientists noticed the eels were far more active than they otherwise would be.

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A closer look showed that it wasn’t just their behavior that had changed. The eels had grown a thicker skin, and a thinner mucous layer over that skin. Their insides had changed as well. The intestinal tract was thicker, and their muscles were more engaged.

More worrying was the change in their hormones: rhe eels were producing more prolactin and dopamine. Cortisol is often released during allergic reactions—it’s part of the immune response. Dopamine inside the brain is a neurotransmitter. Outside the brain, it has many functions, from turning on the immune response to regulating the intestines and kidneys. And in many species, prolactin regulates mating and reproductive behavior. In humans, it’s often associated with lactation. The researcher worry that in eels, it may be responsible for the long voyage they make to the ocean to mate every year. Mess with the eel’s hormones, and eels may become extinct.

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But who’s gonna knowingly feed an eel cocaine, other than scientists? We’re doing so indirectly. An Italian study done showed that rivers have quite a few illegal drugs in them — for instance, a liquid chromatography analysis of the Sarno River turned up morphine, codeine, and lots of cocaine. Granted, only 15 grams a day made it through the river, but that’s sufficient to prompt worry in public health officials about its effect on humans.

What is its effect on eels? We’ll see.

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