“Like cures like…”
The idea of “similia similibus curentur” or “like cures like” lies at the heart of two pseudoscientific medicinal practices that used plant-based and other natural remedies: the Doctrine of Signatures and Homeopathy.
The Doctrine of Signatures centers on the idea that plants look like the body part they are meant to help. For example, hepatica was considered a cure for liver ailments because its lobed leaves resemble the lobes of a liver. It is uncertain whether the Doctrine was used to select plants for medicinal treatments, or if the Doctrine was developed later as a mnemonic device to help people remember and find the plants used to treat various ailments. The resemblance and associated curative properties also influenced common names for various plants including eyebright, birthwort, and liverleaf.
Homeopathy, developed by Samuel Hahnemann, administers treatment via diluted doses of substances that cause similar symptoms to those experienced as part of an illness. Plants – many poisonous – are used in Homeopathic treatments, along with other dangerous substances like arsenic.