1836, "treatment of disease by remedies that produce effects opposite to the symptoms," from German Allopathie (Hahnemann), from Greek allos "other" (from PIE root *al- "beyond") + -patheia, "suffering, disease, feeling" (see -pathy). The term applied by homeopathists to traditional medicine; the formation is much-criticized by purists; the equivalent Greek compound had a different sense and was used in grammar, etc.
<a href="https://www.etymonline.com/word/allopath">Etymology of allopath by etymonline</a>
Harper, D. (n.d.). Etymology of allopath. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/allopath