The commentary on interactions between various conventional medicines and preparations of the herb St John's wort (Hypericum perforatum) in the May issue of Current Problems in Pharmacovigilance, comes as clear warning.
There is a tendency among naive enthusiasts for herbal treatments to believe that any medicine derived from a natural plant is safe. Far from it. This nonsense should have been discarded decades ago, when everyone who had ever studied pharmacognosy to the slightest degree was aware that there are some nasty alkaloids, glycosides, flavonoids and irritant essential oils in the flora of our hedgerows and meadows. The photosensitising potential of hypericum has long been recognised, and handling it during bright summer days has been discouraged.
In the distant past, the wort was chiefly recommended for its alleged powers against all forms of enchantment and particularly evil magic. In country districts bunches of it were hung in windows to avert lightning strikes.
Claims regarding its therapeutic virtues have always been rather vague. Infusions have been recommended for treating catarrh, loss of hair and sprains, while an ointment was claimed beneficial for burns.
John Gerard in his 1597 herbal waxed enthusiastic: "The leaves, floures and seeds stamped and put into a glasse with oile olive, and set in the hot sun for certain weekes together, and then strained from those herbs and the like quantity of new put in, and sunned in such manner, doth make an oile of the colour of bloud, which is a most pretious remedy for deep wounds and those that are thorow the body, for the sinues that are prickt, or any wound made with a venomed weapon."
In about 1990, hypericin derived from St John's wort was subjected to extensive testing in the United States after the claim that it was effective against human immunodeficiency virus and might therefore help patients suffering from AIDS. The great hope was that hypericin might act synergistically with other anti-HIV drugs. Nothing of note seems to have come of this experiment. Then, in 1996, clinical trials were performed to assess the possible value of the wort in treating mild to moderate depression. An article in the British Medical Journal in 1996 stressed the marked difference between German and British medicine in the attitude to the herb, in respect of its value in treating psychological complaints. In 1994 German physicians prescribed some 66 million doses of hypericum preparations in the belief that extracts of the herb were more effective than a placebo against mild to moderately severe depressive disorders. As long ago as 1984 the active principle of St John's wort, hypericin, was recognised as an inhibitor of monoamine oxidase. Average doses of 0.2-1mg of hypericin were claimed to be effective in depressive states, anxiety and nervous excitement. It is difficult, however, to classify psychiatric disorders precisely, and testing was not carried out for long enough periods.
One of the virtues of hypericin was judged to be its relative safety. The most notable adverse effects have been gastrointestinal disturbances, allergic reactions, and fatigue. At present, attention has been concentrated on interactions of hypericum with many conventional drugs, particularly selective serotonin reuptake inhibitors, whose serotonergic effects it may intensify. With most other types of drug, hypericum reduces their blood concentrations and thereby leads to loss of control of the condition being treated.