Plant medicines have often not been tested systematically, but have come into use informally over the centuries.
Plant medicines have often not been tested systematically, but have come into use informally over the centuries. By 2007, clinical trials had demonstrated potentially useful activity in nearly 16% of herbal extracts; there was limited in vitro or in vivo evidence for roughly half the extracts; there was only phytochemical evidence for around 20%; 0.5% were allergenic or toxic; and some 12% had basically never been studied scientifically.[53] Cancer Research UK caution that there is no reliable evidence for the effectiveness of herbal remedies for cancer.[102]