Traditional herbal remedies are used by many patients for selfhealing because they enjoy a reputation as natural products with significant biological potency, which are safer than conventional medicines. Over the past two decades, however, many reports dealing with adverse effects or toxicity of herbal products have been published. Analysis of these reports has been shown that herbal remedies may cause serious gastrointestinal, haematological, cardiac, renal and nervous system adverse reactions and interact with standard drug therapy. In general, both physicians and patients have lack of awareness regarding hazards of herbal products. Physicians should ask patients about use of herbal preparations when a drug history is taken, especially when they have unusual symptoms and signs. On the other hand, people should be educated about rational use of herbal remedies. It means, among other things, not to stop their use, but their abuse.

Traditional herbal remedies are used by many patients for selfhealing. The potential risk of toxicity with herbal products is increased because they are not categorised as drugs (many of them are sold in health food stores and are designed as dietary supplements) and are, therefore, not subjected to standard tests for safety and effectiveness or good manufacturing practice standards that ensure quality control. Many herbal products are imported from foreign countries and often, like some domestic ones, do not have the active or inactive ingredients listed on the package labelling. Besides, many patients use herbal medicines along with standard drug therapy. Since a number of herbal preparations possess one or more pharmacologically active principles it is reasonably to suspect that many of these agents can interact pharmacodynamically and/or pharmacokinetically with prescription and over-the-counter pharmaceuticals. Recently, many reports dealing with adverse effects or toxicity of herbal products have been published.

In this review we present the characteristic examples of herbal products toxicity and their possible interactions with standard drugs and give some recommendations for overcoming this problem

Possible interactions between various xenobiotics (including drugs) and active principles of medicinal plants (13-15)

Herbal medicines may interact with conventional drugs both pharmacodynamically and pharmacokinetically. Informations that widely used herbal products such as St. John's wort may induce drug metabolic enzymes from cytochrome P450 (CYP450) family imply a number of possibilities for herbal product-drug interactions. The examples of known data about influence of active principles from plants on drug metabolizing enzymes are given below:
 

Suggestions for reducing the risk of herbal product adverse effects

For patients

1. Avoid to take herbs if pregnant or attempting to become pregnant without consultation with medical professionals.

2. Avoid to take herbs if you are nursing without consultation with medical professionals.

3. Avoid to give herbs to your baby without consultation with medical professionals.

4. Avoid to take a large quantity of anyone herbal preparation on a daily basis.

5. Buy only preparations when the plants are listed on the packet.

6. Avoid to take anything containing comfrey.

7. Avoid the use of herbal products with standard drugs without consultation with medical professionals.

8. Keep herbal products out of the reach of children.

1. Inform your patients that toxicities can occurred even with therapeutically proven herbals.

2. When take a drug history ask on the use of herbal products.

3. Report the nearest Poison Control Center or Center for Adverse Drug Effects in case of appearance of adverse reactions to herbal products.

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11. Nortier J.L. et al. (2000): Urothelial carcinoma associated with the use of a Chinese herb (Aristolochia fangchi), N. Engl. J. Med. 342, 1686-1692.

12. Kessler D.A. (2000): Cancer and herbs, N. Engl. J. Med. 342, 1742-1743.

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15. Roby C.A., Anderson G.D., Kantor E., Dryer D.A., Burstein A.H. (1999): St. John's wort: Effect on CYP3A4 activity, Pharmacokin. Drug Disp. 67, 451-457.