Ivermectin is an OTC drug in much of the world. Side effects are damn near none. Better safety profile than Tylenol.
It is toxic to some people. It took awhile for doctors to figure out why. They are seeing genetic defects in patients who have problems with ivermectin such as the Multi resistant drug transporter gene. Mdr1.
The problem with pharmocogenics is that it is not advanced enough to keep up with gene testing. You may have 100 variants in a gene known to cause problems but they may not have connected a drug to that variant yet.