properly trained practitioners are able to make fairly reliable checks, at
least visually. Unrecognised contamination by other herbs, drugs and
various chemicals (including heavy metals or insecticides) is another
possible hazard.
In an effort to improve the provenance of Chinese medicinal herbs a field
cultivation project has been set up in Germany.^167 Herbs are grown under
controlled and documented conditions, improving drug safety and material
quality.
CHM has frequently been used as an alternative to orthodox therapies,
especially where the latter have been considered to be ineffectual or have
unacceptable side effects. One of the most popular uses of CHM in the
UK is in the treatment of atopic eczema, particularly in cases resistant to
orthodox therapy. As the herbal medicines are of natural origin, they are
often perceived as being totally safe by consumers, but unfortunately many
TCM remedies are potentially toxic when used in large doses and/or over
extended time periods. Some examples of potentially toxic herbs are given
in the following sections.^168
Examples of toxic herbs
It is estimated that there are 7000 species of medicinal plants in China and, of
the 150 species most frequently used, 10 are toxic.^169 In Hong Kong most
cases of serious poisoning are related to the use of the roots of cao wu
(Aconitum kusnezoffiii), fu ziand chuan wu(Aconitum carmichaeli). These
herbs contain variable amounts of highly toxic alkaloids, including aconitine,
which activates sodium channels and causes widespread excitation of cellular
membranes. Several other herbal preparations containing aconitine alkaloids,
e.g. monkshood (Aconitum spp.), are commonly used in Chinese medicine to
treat arthritic, rheumatic and musculoskeletal pain. The alkaloids have
analgesic, antipyretic and local anaesthetic properties but they are potentially
toxic. The toxic effects include severe cardiac arrhythmias, nausea, vomiting
and general debility. Unfortunately there is only a small margin between
therapeutic and toxic doses. Aconite species are currently classified as a
prescription-only medicine (POM) in the UK for internal use, although they
are allowed for use externally by herbalists.
Anticholinergic poisoning due to the flowers of yang jin hua(Datura
metel L.) and nao yang hua(Flos rhododendri mollis) has been reported.
These herbs, which are used to treat asthma, bronchitis and toothache, may
contain hyoscine, hyoscyamine and atropine, and can cause flushed skin,
dilated pupils, confusion and coma.
Ba jiao lian(Dysosma pleianthum [syn.Podophyllum pleianthum]) is a
species of the May apple that is used for the treatment of weakness and
snake bites. The resin is extracted from the plant rhizome and is thought to
164 | Traditional medicine