Species of frogs have populated the Earth for hundreds of millions of years and have played a key role in human health and medical treatment across the centuries. Many frogs exude toxins through their skin as a means to deter predators and the extraordinary diversity of chemicals has long been of interest to scientists. Ancient Chinese medicine has used dried toad toxins to treat heart conditions as they act in a similar way to digitalis, a plant extract that can trigger heart contractions in the event of cardiac arrest.
Over the past 30 years, scientists in the US have used the venoms of frog and toad species for painkillers and as potential treatments for cancer. Some species of Ecuadorean poison dart frogs create an alkaloid called epibatidine, which works as a painkiller some 200 times more potent than morphine. South American Indians used various kinds of frogs as a disinfectant, by rubbing the secretions of the animals on cuts and wounds. Research is also under way to investigate whether chemicals isolated from the skin of frogs might offer resistance to HIV infection. Frogs have even been used in cloning research and other branches of embryology, because frogs are among the closest living relatives of man to lack eggshells (which are characteristic of most other vertebrates), allowing scientists to observe early development. The skin secretions of some frogs and toads are also known to have hallucinogenic properties. The Colorado River toad and cane toad contain bufotoxins, some of which, such as bufotenin, are psychoactive, and have therefore been used as recreational drugs.