Most naturalists will be familiar with mistletoe as a semiparasitic plant (it can photosynthesise but also derives nourishment from its host) that grows on a variety of trees, notably lime and apple.
The leaves and small twigs of mistletoe are used in
herbal medicine as a tranquilliser and to reduce blood pressure. 
A variety of
compounds in this plant have effects upon the heart and blood vessels. There
appears to be a ‘beta-blocker’ type of action; also a stimulation of the vagus
nerve to slow the heart rate. The remedy is often combined with lime flowers
and hawthorn: lime flowers are calming while hawthorn is beneficial in all
heart conditions.
The berries are of course poisonous and not used by lay herbalists. However, some medical practitioners use mistletoe extracts that include the berries as a treatment for cancer. One of the best known of these is the homeopathic preparation known as Iscador. While there is good evidence that mistletoe extracts can kill cancer cells in vitro, and also have immune stimulating properties, their use in cancer treatment remains controversial and the evidence for their efficacy is not conclusive.
In an age of evidence-based medicine, those who seek evidence for the efficacy of ‘whole plant’ remedies, face this problem: how are high quality research and large scale trials to be funded into remedies that grow all around us and cannot be patented?
Medical Herbalist
© 2003 Suffolk Naturalists' Society