There has been a substantial growth in the use of herbal medicines in parts of the world where it was not used extensively in the past. There are many reasons why people use herbal medicines. According to a survey in the USA people use herbal medicines because they prefer natural products [47%], there are fewer side effects [17%], it is more efficient [17%], it is less expensive [10%] and it is milder [8%]. At least in his group of consumers price was not a major factor (McCaleb, 2000
Robbers and Tyler 
distinguish between paraherbalism, which is based on pseudoscience, and rational herbalism where herbal medicine is used based on scientifically verifiable evidence. In paraherbalism, which includes homeopathy as “a particularly pernicious form of paraherbalism”, the effects achieved could be due to a placebo effect or are at least not reproducible and scientifically verifiable at this stage. On the other hand rational herbalism is based on plants containing relatively low concentrations of pharmacologically active compounds that can be evaluated in clinical trials. Herbal medicines as are therefore in effect dilute drugs.
The main factors that limit the rational use of herbal medicine on the same level as pharmaceutical products are [a] the efficacy of the herbal medicine has to be proven, [b] the safety of the herbal medicine has to be proven and [c] the quality control of herbal medicines have to be improved.
The strong growth of the herbal medicine market for long periods may be an indication of efficacy of herbal medicine even though clinical trials may not have taken place. Due to the difficulty of patenting herbal medicines, funding restricts adequate clinical trials to prove efficacy. Some registering authorities are more concerned with safety than with efficacy and accept that because traditional healers have used plants to treat people in fact informal clinical trials have been taking place over many years. It is frequently accepted that traditional healers have collected their information over hundreds even thousands of years. In many cases however, relatively recently introduced invasive or domesticated species are used. Furthermore the many claims for being able to treat a new disease such as AIDS shows that “informal clinical trials” are constantly undertaken regardless of any possible legal or ethical problems.
As far as safety is concerned, herbal medicine has been used for centuries by rural people and for decades by urban people and is frequently considered to be safe. For many herbal medicines approved in the German Commission E Monographs [Blumenthal et al., 1998] as prescription medicines, no clinical trials or long term toxicity studies have been carried out. Care should be however taken when a different extractant is used because the extractant has a major effect on the compounds extracted and biological activity of a plant extract (Kotze and Eloff, 2002
Quality control is therefore one of the major problems in the rational use of herbal medicines. With many herbal medicines the active component is not known and genetic and environmental factors may influence the concentration of plant secondary compounds. Frequently a marker compound is selected and this is used to determine the quality of the herbal medicine.
In a study in North America no samples of feverfew (Tanacetum parthenium
) examined contained the 0.2% parthenolide required for activity [Groenewegen and Heptinstall, 1986
]. With more people collecting and distributing medicinal plants, the wrong plant is frequently offered either as a genuine mistake or in an effort to increase profits. In one study of 54 ginseng products, 60% were worthless and 25% contained no ginseng at all [Liberty and der Marderosian, 1978
]. One of the important components of quality control is therefore to validate the identity of the plant in the product. High performance liquid chromatography is valuable to quantify chemical compounds in plant extracts, but planar chromatography also know as thin layer chromatography [TLC] has many advantages and is cheaper and easier to use than HPLC to identify plants by analyzing the chemical components of extracts. Wagner and Bladt (1996)
did pioneering work in providing a TLC atlas of many herbal medicines with colour photographs of the chromatograms of plant extracts. They collated the methods developed by different scientists over many years. The methods compiled by Wagner and Bladt 
lists 17 different extractants 41 different TLC solvent systems, including several types of TLC plates and 44 different detecting spray reagents. Many of these procedures were targeted towards isolation and separation of the active compound in the specific medicinal plant. Some TLC methods specified in publications such as the British Herbal Pharmacopoeia do not include plates of the chromatograms and only provides an Rf
Earlier results within the Phytomedicine Programme have shown that acetone is probably one of the best solvents to extract compounds of a wide range of polarity from dried plant material [Eloff, 1998
]. In this study we compared acetone extraction with methanol under reflux extraction with a few selected medicinal plants. We developed additional TLC solvent systems to separate compounds with a large variation in polarity and also investigated different spray reagents for the TLC chromatograms. Finally we extracted and separated 83 commercially used herbal medicines representing close to 60 different medicinal plants.
Although sub-Saharan Africa and the Indian Ocean islands contain about a quarter of the worlds plant species, only 7.6% of the commercialized medicinal plants are from Africa (van Wyk and Wink, 2004
). The values for Asia are close to 40%. The reason is probably because the indigenous knowledge on African medicinal plants has not been documented. The Association for African Medicinal Plant Standards (AAMPS) a non-profit organization based in Mauritius has been established to promote the use of African medicinal plants in Europe and the USA [www.aamps.org]. AAMPS has identified the 50 most important African medicinal plant species in consultation with many stakeholders and with funding from the European agency Commission for the Development of enterprise (CDE). Trading standards/monographs on these species have been completed and the first edition of an African Herbal Pharmacopoeia has been published with funding from several European Union Agencies. The information is available on the website (www.aamps.org
). The techniques developed in this contribution have been used in the African Herbal Pharmacopoeia.