Patients don't have a right to whatever medicine they want, since many medications would be harmful to the patient and/or society at large if they were freely available. That's why prescriptions exist.I am talking about the autonomy of the patient. Many of us live in countries in which patients can decide to get the genitals cut off if they so desire. A patient should be able to get ivermectine, even if the effect is only a placebo effect.
For example, a patient doesn't have unrestricted access to antibiotics when suffering from the flu. Not only would it not do anything and be a waste of resources (since the flu is caused by a virus, not a bacterium), but there can be objective harm to the patient from overusing antibiotics (killing good bacteria, increasing the odds of Clostridioides difficile, etc.), and there can be objective harm to society (increasing the rate at which antibiotic-resistant bacteria develops, etc.).