DANGERS: Prolonged use of this tea may render skin sensitive to exposure to light. It is this 'side effect' that shows that Yarrow tea has some mild psychotropic effect. A couple of cups of this tea and you may notice a shift in colour and intensity of light around you. For artists or photographers this photosensitiser can sometimes provide a useful shift in perception. However, another name attributed to Yarrow is 'Devil's Plaything' - one suspects that this name was given to several herbs used by witches or 'Wise Women' who were systematically exterminated in middle-ages.

Yarrow leaves have also been used in tobacco or snuff mixtures and a decoction rubbed into head is said to delay balding. To make Yarrow tea add two or three fresh or dried leaves per person to boiling water and leave to infuse for 5 minutes or so. Sweeten this with honey if you like. Some people like it with a slice of lemon to give this 'tisane' a clean edge.

The Woolly Bear caterpillar has also been observed to change its diet according to whether it is infected by a particular parasite. Normally a Lupin eater, caterpillar increases its chance of surviving a particular fly parasite by changing to a diet of Poison Hemlock. Self-medication is not therefore a 'rational choice' in other species, but a carefully integrated part of a survival mechanism against an invisible predator - disease. Humans seem to have lost this sense of their own health and are not usually informed as to uses of plants growing around them.

Humans often self-medicate though - alcohol indulgence to deal with stress being an obvious example of this or ready availability of pharmaceutical or street drugs. We often consume substances such as caffeine or sugar drinks for easy energy. The natural trait towards self-medicating may well be at basis of many of our unconscious 'eating choices'. Potatoes contain a form of opiate and all foods to some extent can act as 'alteratives' to a unique physiology. We talk about comfort foods and rewarding ourselves with treats to eat. Often we might have a favourite food that can help if we feel too ill to eat, like scrambled egg. This is a unique food because it contains all of amino acids we need to digest it. Chocolate is to many ultimate comfort food treat.

An extreme example of what we do is shown in 'Pica' where a person gets uncontrollable desires to eat certain edible (and inedible) substances. This condition occurs in pregnant women and is thought to express need for particular minerals. Because our food sources are often limited to processed (and demineralised) food, and because of destruction of herbal folk-lore and access to wild medicine, many of us have lost touch with our 'health sense' and an ability to use food or wild plants for self-medication. A regular preventative 'detox' was an essential part of our diet at one time and if you like taste of mothballs you could even try Tansy cakes.

Article with thanks to Roger Phillips and Michael Hoffman