Materia medica is a Latin term for any material or substance used in the composition of curative agents in medicine.

The use of materia medica was historically based upon the idea that medicines possess magical curative powers — the original mechanism of action for all materia medica was magic. Folk healers among the peasantry believed in the law of signatures to identify which herbs would be effective against which diseases.

By a process of trial and error, folk healers learned which herbs worked and which herbs did not work. Materia Medica eventually developed into the science of pharmacology.

The term materia medica is still used in homeopathy, which uses minute dosages of materia medica in its medicines, and in herbal therapy.