To my understanding, this came about because of people trying to self treat with it and the most accessible way for a lay person to get access was the aforement

To my understanding, this came about because of people trying to self treat with it and the most accessible way for a lay person to get access was the aforementioned horse medicine (which came with dosages way above those for people) I.e. it's not that ivermectin is horse medicine in all forms, but the forms of it which the people were taking in response to Trump's early promotion were horse medicine