SEATTLE — “Chris C.” recently offered tips on how to use a horse deworming drug “good enough to prevent or treat o-vid” in a comment on an Amazon product page.

While the Food and Drug Administration has warned against human use of the animal version of ivermectin, the misspelling, typically used to avoid detection across social media sites blocking coronavirus misinformation, worked on Amazon.

People like Chris are fueling a new wave of misinformation on Amazon’s site by using slightly altered spellings in reviews and comments that evade the company’s efforts to crack down on dangerous advice.

Amazon has struggled to police scammy sellers on the site for years. The company leans on technology, such as algorithms trained to detect words or phrases that could indicate violations of its rules, to prevent misinformation. Some humans are involved, Amazon said, although it declined to provide numbers or details.

But now users — sometimes directed from social media sites like Facebook — are taking a more active role in sharing misinformation in the midst of the coronavirus pandemic. Slight misspellings and misdirections can trick Amazon’s detection technology, leaving questionable and sometimes dangerous suggestions about how to use a product online for weeks or more.

The Washington Post found multiple examples of misinformation on the site touting use of the horse formulation of ivermectin to treat covid-19. Previously, customers have used the site to give a wink and a nod to products containing cannabidiol, or CBD, which is not allowed on the site, The Post has reported. And conspiracy theorists have latched onto book reviews to spread misinformation, for example in 2015, raging that the Sandy Hook school shooting was a hoax in comments on books about the massacre.

Amazon removed the ivermectin posts flagged by The Post, and spokesman Craig Andrews said the company actively moderates reviews and removes inappropriate content when it is identified.

(Amazon founder Jeff Bezos owns The Washington Post.)

Amazon has long allowed customers to leave reviews — even negative ones, with the belief it will promote trust in the site. Executives believe positive reviews give hesitant customers incentive to buy products, said a former Amazon retail executive who spoke on the condition of anonymity to talk candidly about internal policy.

“The reviews are the gas,” the former executive said.

That might be one reason Amazon has been slow to remove reviews that promote ivermectin as a covid-19 treatment, said Trevor Pinch, a Cornell University science and technology professor who has studied Amazon’s review system.

“If they were concerned about the abuse of the system, they’d be onto this,” Pinch said. “I don’t think they are concerned. They just want to sell the product.”

At the start of the pandemic, Amazon vowed to remove product listings that claim to ward off the coronavirus, only to find creative sellers sidestepping the company’s detection by putting false claims in product listings’ image galleries.

In this case, however, the ivermectin available on Amazon is a safe product when used to treat horses. None of the third-party merchants selling the horse formulation on Amazon appear to be pushing the product for use in humans. Ivermectin sales have soared on the site, hitting $3.2 million last month, compared with $184,073 in August 2020, according to data from Jungle Scout Cobalt, which tracks Amazon sales data.

An anonymous customer wrote in July about using it on “my ‘mini horse’” and noted that the drug’s “suppression is a crime against humanity.” And in response to a shopper’s question about why the drug’s price has doubled, an Amazon customer who goes by the handle Diesel wrote, “Because it has been Proven to prevent c19.”

The FDA has not approved ivermectin to treat or prevent covid-19. Meanwhile, calls to poison control centers around the country about ivermectin exposure jumped this summer. (Ivermectin, in low doses, is given by prescription to humans to treat lice, scabies and other parasites.)

Some of the promotion for ivermectin on Amazon as a covid-19 treatment appears to be fueled by social media platforms, according to analysis by the left-leaning advocacy group Media Matters. The organization turned up posts in Facebook groups directing members to Amazon to buy the product, and offering dosage recommendations for the deworming paste.

A post in one group called “Ivermectin & how it worked for me” discussed taking the horse formulation, purchased on Amazon, prophylactically. Another post in the “IVERMECTIN MD TEAM” group gave human dosage advice after a query about using the horse paste bought on Amazon.

“In addition to sharing methods how to get it, they are sharing methods how to use it,” said Kayla Gogarty, associate research director for Media Matters.

Facebook’s policy bars users from claiming that ivermectin is a cure for covid-19, spokesman Aaron Simpson said in an emailed statement.

“We remove content that attempts to buy, sell, or donate Ivermectin,” Simpson said.

Posting comments about Amazon products is simple. Every product page offers anyone, whether they purchased the product or not, the space to write a review. And people can answer customer questions on product pages just as easily, by clicking on a specific question to enter a response. Users are supposed to abide by Amazon’s Community Guidelines, which prohibit people from posting content that, among other things, “encourages or supports the dangerous misuse of a product.”

The large social media platforms such as Facebook, Twitter and YouTube employ thousands of content moderators, who often sift through the most vile content on the Internet to stop it from ever reaching those companies’ customers. Amazon also has workers who moderate content, but company spokesman Andrews declined to disclose how many. Amazon’s systems stopped more than 200 million suspected fake reviews last year before they were seen by customers, he said.

Amazon’s own algorithms have also fueled searches for ivermectin as a covid-19 treatment. One seller earned the “Amazon’s Choice” tag — a designation automatically driven by such factors as popularity, product availability and customer reviews — for searches on “duramectin ivermectin for humans.” (Duramectin is the brand name for an ivermectin paste that’s used for horses.) And on Monday, a search on Amazon for “duramectin ivermectin for humans” turned up 92 listings.

The Verge earlier reported that Amazon’s autocomplete feature drove shoppers to ivermectin products.

Amazon’s Andrews said the company has since taken steps to address the issue. Any search queries for ivermectin now lead to a notice that reads, “The FDA advises against the use of ivermectin to treat or prevent COVID-19.” Amazon also has changed the way its autocomplete feature fills in search queries, preventing ones that imply that ivermectin can treat covid-19, Andrews said.

“Amazon’s autocomplete responses are driven by customer activity,” he wrote. “We are blocking certain autocomplete responses to address these concerns.