There’s an interesting story of how a medicinal plant inspired the discovery of the pharmaceutical drug metformin, which is currently used in the management of type 2 diabetes.
Goat’s rue (Galega officinalis) is an herb that was used in traditional medicine since the Middle Ages to treat diabetic symptoms. The first scientific studies of the chemical constituents of goat’s rue found a variety of alkaloidal guanidine derivatives that were putatively responsible for its pharmacological effects. However, they tended to be quite toxic. One of them, galegine, was found to be less toxic. It was identified as isoprenyl guanidine and it was studied clinically in the 1920s. These trials showed blood glucose lowering effects in diabetic patients, but were ultimately unsuccessful, primarily due to a short duration of action.
This work inspired further investigation and the biguanides were identified as compounds with greater potential. Three of them, phenformin, buformin, and metformin, made it to the market. Phenformin and buformin have since been withdrawn, but metformin is still the drug of choice for management of type 2 diabetes.