Earlier this month, a Tweet from author Rachel Sharp alerted the Internet to a disturbing trend: Some people were resorting to taking fish antibiotics to cure their ailments. Yes, fish antibiotics. Sharp’s Tweet, which quickly went viral, included a screenshot of several thinly veiled Amazon reviews left by humans who were clearly using the aquatic pet medicine Moxifish on themselves.

Naturally, the Internet was appalled. But few stopped to ask: what’s actually so wrong with taking fish antibiotics?

How bad is American healthcare?



Read the reviews for aquarium antibiotics and decide for yourself. pic.twitter.com/DT8wuq4iHg — Rachel Sharp (@WrrrdNrrrdGrrrl) July 30, 2017

It’s not quite as crazy as it sounds. Fish are given many of the same antibiotics as humans—amoxicillin, ciprofloxacin, penicillin and more—sometimes even in the same doses. These pills, which are intended to be dissolved in fish tanks and be absorbed through fishes' skin, can also look extremely similar to the human versions. And while a trip to the doctor can rack up hundreds of dollars for someone who doesn't have insurance, a bottle of 30 500mg capsules of Moxifish costs just $29.95 from the supplier, Fishceuticals.

But there are a few key reasons why taking your fish’s drugs is a very bad, no good idea. Let’s start at the top.

First, fish antibiotics are completely unregulated. Technically, they should fall under the purview of the Food and Drug Administration, which oversees both human and animal drugs. Those animals including companion animals (dogs, cats, horses) and food animals (cattle, pigs, chickens). Yet no ornamental fish antibiotics are approved by the FDA.

"The antibiotics available in pet stores or online for ornamental fish have not been approved, conditionally approved, or indexed by the FDA, so it is illegal to market them," the FDA said in a statement to Smithsonian.com. The statement continued:

If consumers are seeing these products in stores, they should be aware that these products have no assurance of purity, safety or effectiveness. The FDA does not have any information about the unapproved antibiotics sold in pet stores because they have not been evaluated for quality, safety, effectiveness, or purity. We strongly advise people to not substitute them for approved products that are intended for use in humans as prescribed by their health care provider.

Why aren’t they regulated? According to some veterinarians, they’re simply too small of a problem for the agency to bother with. Pet fish antibiotics make up a tiny fraction of the total amount of antibiotics used, says Samuel Young, a veterinarian and founder of the Uncommon Creatures Mobile Veterinary Services, which treats animals from fish to gila monsters to llamas. Thus, pet fish meds don’t pose nearly the same risks as antibiotics used for food animals, which the FDA is currently working to regulate more tightly.

The FDA says that it does not have any data on how prevalent the fish antibiotics problem is. "We are currently looking into these products," representatives wrote in a statement. "FDA considers taking action based on its resources, the risk the product poses, and its public health priorities."

Lacking the stamp of FDA approval, fish meds instead often sport claims that they are pharmaceutical or “USP grade,” a supposed quality benchmark set by an independent non-profit called the United States Pharmacopeia. The USP, however, is not a regulatory agency. Though it tests a small number of supplements through its "USP verified" program, it does not otherwise measure the purity or content of drugs for their purported contents.

"I think it's probably mostly B.S." Young says of these grades. "[Companies] are not able to guarantee—or even required to guarantee—what's actually in it, the purity of it, or the actual amount of it. It can be anything."

According to the FDA’s website, the agency hopes to someday help make more of the medications given to "minor species," which include fish, legally available and therefore regulated. But for now, Young describes the field of fish medicine as being in its infancy. He likens the situation to the early days of the livestock industry, when farmers could purchase a range of medications without a prescription. "We're still figuring out what works for fish and what kind of diseases we're treating," he says.

But even if fish meds were labeled as human-grade medicines, using them to self-medicate would still be a bad idea.

When a doctor prescribes you antibiotics, the first step is to make sure you’re dealing with a bacterial infection by running the proper tests. Antibiotics, which are intended to kill or slow the growth of bacteria that cause infection, are useless against a virus—and you don’t want to use them if you don’t have to, or it might lead to bacterial resistance.

The next step is to find out what kind of bacteria you’re up against. Even broad spectrum antibiotics work differently to target different kinds of infections. Moxifish, for instance, contains amoxicillin, a type of penicillin. When a fish absorbs this compound through their skin, it travels through the bloodstream until it latches onto a bacteria’s rigid cell wall. There, it interferes with wall-building, leading to a build-up of pressure that eventually causes the the cell to burst. Unfortunately, many types of bacteria have grown resistant to penicillin: Staphylococcus Aureus, the bacteria commonly responsible for skin infections no longer responds to this class of antibiotics.

Other fish antibiotics, such as API's Erythromycin, are known as macrolides. These compounds destroy bacteria by targeting the protein-building structures of the cells. Without proteins—which act as messengers, structural supports, transporters, storage and more—the cell dies. Another antibiotic class called Quinolones, which include the fish drug Fish Flox, inhibit bacterial cells from copying their DNA, thus preventing the colonies from multiplying. Quinolone are used to treat a range of infections including urinary tract infections, but in recent years many bacteria have begun to develop resistance.

Matching the right antibiotic to the right illness is crucial. “Let's say the antibiotic is correct, that capsule contains the right amount of medicine, and it’s a good quality medication and its able to be absorbed into the system,” says Wilson E. Gwin, director of the Purdue Veterinary Teaching Hospital Pharmacy. “We don't really know if that's the right drug for what the person is trying to treat. If it's the wrong drug, they can do themselves even more harm.”

Choosing the right med is also difficult. Learning the particulars of each antibiotic is "an exhausting part of medical school," says Daniel Morgan, a physician and epidemiologist at the University of Maryland. "It's a bit like learning verb tenses in a language."

So what if you skip the doctor, take a gamble and choose wrong? Well, each drug comes with its own set of potential side effects and allergic reactions. Taking amoxicillin while suffering a viral infection such as mono, for instance, can cause the body to erupt in rashes, says Morgan. Ciprofloxacin, previously a go-to for UTIs and sinus infections, has come under recent scrutiny for causing lasting damage to tendons, muscles, joints, nerves and the central nervous system. Many other antibiotic classes come with their own unpleasant effects.

And even choosing correctly doesn’t guarantee success.

There’s a reason that bacterial resistance is a major public health problem: Bacteria are hardy foes that adapt rapidly to the changing environment of you. Sometimes, when they divide, they end up with useful random mutations, which they can pass down to future bacterial generations in a matter of hours. Other times, they get genes that are transferred from already resistant bacteria. "As a result, each new progeny becomes a resistant one and a potential donor of resistance traits to new recipient bacteria," writes Stuart B. Levy, a microbiologist and drug resistance expert at Tufts University, in his book The Antibiotic Paradox.

Using these processes, the ingenious invaders eventually develop specific adaptations as they multiply that can tackle and even degrade the antibiotics. Some even take on genes that code for tiny "pumps," which actively eject antibiotics from the bacterial cell. "Bacteria are not there to be destroyed; they're not going to give up," Levy says.

Finally, antibiotics kill off both good and bad bacteria. That means that, to avoid unwanted side effects, it's crucial to take them for the proper amount of time. Ending an antibiotic regimen too soon—or taking one for too long—can both breed further bacterial resistance. Stop too soon and you risk relapse, potentially allowing the microbes causing the disease to proliferate and form resistance. But take antibiotics for too long, and you might be giving the bacteria greater amounts of time to develop ways to elude the meds, recent studies suggest.

In short, you don't want to mess around blindly with your bacteria.

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And yet, humans raiding the medicine cabinets of our finned friends is by no means a new trend. As Levy documents in his book, the practice stretches back to at least the 90's. While investigating antibiotics misuse, Levy describes a conversation with a pet store owner who admitted to taking the fish antibiotics for an infected finger—noting that the practice wasn't unusual among other pet store workers.

In 2002, Army physician Brandon J. Goff wrote a letter to the editor of the New England Journal of Medicine documenting an encounter with an unnamed Army Special Forces soldier who came to him with a sinus infection after self-medicating with fish antibiotics from a pet store. The soldier described this source of antibiotics as "common knowledge among all branches of the American Special Forces community," according to Goff.

In the years since, many pet stores have wised up to the trend and quietly removed these antibiotics from their shelves. PetSmart representatives told Smithsonian.com that the company had limited its selection to "fish medication in forms that could not easily be consumed by humans. This allows us to provide fish medication to the customers who need it for their aquariums while helping to prevent misuse." (The company did not say when they made the change and did not respond to a follow-up request.) In the last week, Amazon has also removed these antibiotics from their site last week in the wake of Sharp’s Tweet; the company declined to comment about the move.

Unfortunately, fish antibiotics are still well within reach. A quick Google search for fish antibiotics pulls up a range of other sources, including Walmart and Thomas Labs. And many Youtube videos, blogs and websites provide guidance for humans seeking out information on taking fish medications for their own personal use. These often target Doomsday preppers—people who stockpile medical supplies and other necessities in case of a society-ending catastrophe—but reddit and other online forums show that the fad isn't limited to those preparing for the end of days.

Sure, some people using fish meds may get lucky, says Morgan. And others may experience few effects, good or ill. But if you are taking fish antibiotics, you’re playing a dangerous game, and you’re playing it with your health. "People will always find different ways to get at things that they think maybe helpful,” says Morgan. “The issue is you need to balance potential harms and benefits … I would guess that there are people out there who have been harmed by doing it."

"We're not talking about a 50 cent or $200 fish—we're talking about a human life,” adds Gwin. “You really are taking a chance. Is it worth it?”

Editor's Note, August 2017, 2017: This post has been updated to include follow-up from the FDA.