Abstract: Protocol violations in López-Medina et al.: 38 switched ivermectin (IVM) and placebo doses, failure of blinding, widespread IVM sales OTC in Cali, and nearly identical AEs for the IVM and control groups David E Scheim, a Jennifer A. Hibberd, b Juan J. Chamie-Quintero c re: López-Medina et al., Effect of Ivermectin on Time to Resolution of Symptoms Among Adults With Mild COVID-19: A Randomized Clinical Trial (JAMA, 2021; links to study paper and supplements are below).1 Abstract A randomized controlled trial for treatment of mild cases of COVID-19 conducted in Cali, Colombia reported no statistically significant differences in outcomes for its ivermectin (IVM) and placebo arms. A striking anomaly, however, was that certain adverse events (AEs) that are distinctive for the study’s high-dose IVM use occurred at nearly identical rates in its IVM and placebo arms. The backdrop for these indicators of IVM use in study controls was widespread sales of IVM for COVID-19 in the Cali area during the study period, with 1.6 IVM doses sold over the counter for each case of COVID-19. The study compounded these risks of contamination of the control arm with critical errors in blinding and segregation of IVM v. placebo doses. A labeling error substituted IVM for placebo doses of 38 patients. Also, 5% dextrose solution was used for the first 64 patients in the placebo group, easily distinguishable from bitter tasting IVM. Given widespread availability and sales of IVM in Cali, lapses in segregation and blinding of IVM and control doses, and IVMcharacteristic AEs in controls, the integrity of the study’s control arm was violated. Some useful information can nevertheless be salvaged from outcomes of this study’s IVM treatment arm, which had 0 deaths and generally mild symptoms, with AEs typical for high-dose IVM (replicated in the control group) that were generally mild and transient.