In April 2020, researchers at Monash University discovered in a pre-print paper that a common anti-parasitic drug called ivermectin could kill the novel coronavirus SARS-CoV-2 within 48 hours in a petri dish (in vitro). The press release cautioned that a successful in vitro experiment says nothing about its suitability for treating COVID-19 in humans. As this drug is commonly used to treat common animal diseases such as Dirofilaria immitis the FDA rushed out a letter expressing concern that people would, in desperation, take ivermectin regardless of whether or not it actually worked, and were particularly concerned that they would take ivermectin intended for animals, which had not been tested in humans, and thus may pose additional dangers. Similar to hydroxychloroquine, by mid 2021, the evidence was not very strong that ivermectin was very effective, with only a few smaller studies showing positive effects and larger, more solid trials tending to produce equivocal evidence at best.
Similarly to hydroxychloroquine, however, this hasn't stopped many people, including political world leaders, from promoting the drug as a cure for COVID-19 to various degrees. Latin American politicians embraced the drug, with the drug being recommended by governments in Peru, Bolivia, and Brazil (albeit with Peru and Bolivia acknowledging that the evidence that the drug worked against COVID-19 was slim). Far from helping out the situation, however, there is evidence that Peru's use of self-medication with ivermectin (along with chlorine dioxide or bleach, anticoagulants, and other snake oil) actually may have increased pandemic deaths. The Indian states of Goa and Uttarakhand, against the advise of the World Health Organization actually gave the drug to much of its residents in May 2021, despite the lack of scientific evidence. Ivermectin was part of a cocktail of unproven drugs promoted by Jair Bolsonaro to fight COVID-19; his promotion of pseudoscience and disdain for proven pandemic methods (e.g. lockdowns and facial mask use) led to Brazil having among the highest death rates from COVID-19 in the world in early- to mid-2021.
In the United States, Senator Ron Johnson led the charge to promote ivermectin as a cure for COVID-19, calling for a hearing in December 2020 to promote the drug. Johnson continued to promote the drug in 2021, appearing at the Milwaukee Press Club on June 3 to, among other things, promote ivermectin and hydroxychloroquine. After uploading the video from the press club event to YouTube, YouTube responded by suspending Johnson's account for 7 days for promoting medical bullshit. Bullshit claims regarding ivermectin were echoed throughout June and July 2021 by some of the more noted anti-vaccination and anti-face mask Fox News personalities (such as Tucker Carlson and Laura Ingraham), as well as explored in noted broscience promoter Joe Rogan's podcasts.  Carlson even went as far to promote on his show a former evolutionary biology professor named Bret Weinstein (brother of Eric Weinstein, and who was also more noteworthy at that time for spreading misinformation about COVID-19 than any accomplishments in biology academia), who bizarrely claimed that ivermectin actually mooted the Emergency Authorization Use for the COVID-19 vaccine for some reason.  On social media, Facebook in particular allowed groups dedicated to spreading false bullshit about ivermectin to proliferate, and even allowed ad buyers to directly target the social network's users who bought into the ivermectin snake oil. 
Because of this, experimental usage of livestock formulations of ivermectin (which, being formulated for a large animal like a horse or a cow, consisted of a much higher dose than pharmaceutical formulations of ivermectin to treat human worm diseases) increased during the summer of 2021, particularly those among the anti-vaccination movement who refused to get the COVID-19 vaccine (which at this time was widely available in the United States, but was disproportionately being rejected by conservative Donald Trump voters).  Consequently, in late August 2021, there was a noted spike in calls to the poison control centers of multiple states concerning overdoses of ivermectin.  According to the FDA, this even included multiple hospitalizations.  Feed stores all across the United States were struggling to keep ivermectin in stock. 
This led to an unusually blunt tweet from the FDA on August 21, 2021 reminding people to not partake in this reckless experimentation, which simply stated: "You are not a horse. You are not a cow. Seriously, y'all. Stop it."  Despite this tweet, the misuse continued. On September 1st 2021 in rural Oklahoma, a doctor reported that the emergency rooms were backed up so badly with ivermectin overdose cases that gunshot victims were "having a hard time getting to facilities" and ambulance systems were "stuck at the hospital waiting for a bed to open". 
- Conservapedia "an off-patent (generic), inexpensive medication which is considered by some to be an effective treatment for COVID-19 as suggested by numerous, constantly updated studies compiled online and by peer-reviewed studies worldwide" - wow.
- RationalWiki has only a section on the subject, but it gives a good overview of the nontroversy
- 2021-09-08 Better Data on Ivermectin Is Finally on Its Way "Studies have been small and often not great. The best info so far says don’t use it, get vaccinated, and hang in there for the more promising meds being tested."
- 2021-08-31 Why Are People **REALLY** Taking Horse Dewormer for COVID-19? (Rebecca Watson): a scientific deep dive
- 2021-08-24 Let's talk about the feed store and public health.... (Beau of the Fifth Column)
- 2021-08-21 YES! Rachel Maddow Fractures FOX News For Hawking a Horse Dewormer as a COVID Cure
- 2021-07-28 [L..T] Why Is the FDA Attacking a Safe, Effective Drug? «The Food and Drug Administration claims to follow the science. So why is it attacking ivermectin, a medication it certified in 1996?» Short Answer: It isn't, and this opinion-piece is stuffed full of misleading claims.
- "Lab experiments show anti-parasitic drug, Ivermectin, eliminates SARS-CoV-2 in cells in 48 hours", Monash University press release, 2020 April 3
- "FDA Letter to Stakeholders: Do Not Use Ivermectin Intended for Animals as Treatment for COVID-19 in Humans", product safety information, 2020 April 10
- "Ivermectin As a COVID-19 Therapy" by Derek Lowe, Science Translational Medicine, 2021 June 7
- "Latin America’s embrace of an unproven COVID treatment is hindering drug trials" by Emiliano Rodriguez Mega, Nature, 2020 October 20
- Self-medication increases pandemic deaths in Peru by The Economist, 2020 October 3
- "Indian State Will Offer Ivermectin To Entire Adult Population — Even As WHO Warns Against Its Use As Covid-19 Treatment" by Siladitya Ray, Forbes, 2021 May 11
- "Indian States Turn to Ivermectin in COVID Crisis" by Kristina Fiore, MedPageToday, 2021 May 18
- "The COVID-19 Pseudoscience Suffocating Brazil" by Kiratiana Freelon and Shanna Hanbury, Medscape, 2021 June 09
- "Republican Sen. Ron Johnson touts alternative COVID-19 treatments at hearing" by Associated Press, 2020 December 9
- "YouTube suspends Ron Johnson for 7 days" by Tal Axelrod, The Hill, 2021 June 11
- "Tucker Carlson Hyped These Fringe COVID Theories. The Science Just Fell Apart" by Corbin Bolies, Daily Beast, 2021 July 16
- "The FDA Is Begging You Not to Take Horse Dewormer for Covid-19" by Peter Wade, Rolling Stone, 2021 August 21
- "Some people are taking an anti-parasitic to treat COVID. Here’s why that’s a bad idea" by Katie Camero, Miami Herald, 2021 August 6
- "Biologist to Tucker: If Ivermectin proven effective against COVID, it moots vaccine push" by Charles Creitz, Fox News, 2020 July 10, archived at archive.org
- "Facebook's Ivermectin Groups Are Unhinged and Out of Control" by Tim Marchman, Vice, 2021 August 26
- "Facebook Is Allowing Ivermectin Ads at a Time When It Really Shouldn’t" by Anna Merlan, Vice, 2021 August 23
- "How anti-vaxxers weaponized Ivermectin, a horse de-wormer drug, as a COVID-19 treatment" by Nicole Karlis, Salon, 2021 August 9
- "Risks rise as vaccination gap with Trump counties grows wider" by Nathaniel Weixel, The Hill, 2021 July 6
- "More Mississippians Using Ivermectin For Livestock Against Covid-19, Then Calling Poison Control" by Bruce Y. Lee, Forbes, 2021 August 21
- "An animal dewormer to treat COVID? Poison control centers see uptick in calls; stores sell out" by Asha C. Gilbert, USA Today, 2021 August 24
- [https://www.fda.gov/consumers/consumer-updates/why-you-should-not-use-ivermectin-treat-or-prevent-covid-19 "MWhy You Should Not Use Ivermectin to Treat or Prevent COVID-19", FDA.Gov
- "Tallahassee feed store, poison control see surge in calls for livestock dewormer used as COVID treatment" by Ana Goñi-Lessan, Tallahassee Democrat, 2021 August 27
- "You are not a horse. You are not a cow. Seriously, y'all. Stop it.", @US_FDA, Twitter, tweet posted on 21 August 2021, archived at archive.is on 2021 August 21
- "Patients overdosing on ivermectin backing up rural Oklahoma hospitals, ambulances" by Katelyn Ogle, KFOR, 2021 September 1