**5. Toxicity of chemicals**

Toxicity refers to the relative ability of a substance to cause adverse effects in living organisms [13]. It may also be defined as the extent to which an exposed tissue is damaged by a chemical substance and covers the effect on a whole organism and sub-structural component of an organism such as the cell (cytotoxicity) or organ (organotoxicity). Toxicity may further be defined to cover the study of the adverse effects of chemicals on living organisms as well as their symptoms, mechanisms and treatments. Toxicity studies may be classified as acute, subacute/subchronic and chronic effects depending upon the quantity and duration of administration of the agents [14].

Similarly, *Momordica charantia*, a known anti-diabetic and antimalarial plant but also used in Ghana as an abortifacient [21, 22], has reportedly caused deadly hypoglycemia in children [23].

Toxicity and Safety Implications of Herbal Medicines Used in Africa

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The basis for the medicinal use of the plants is the presence of mixtures of different biologically active plant constituents or phytochemicals (secondary metabolites) such as alkaloids, glycosides, terpenoids, and so on that may act individually, additively or in synergy to demonstrate an effect which may be useful or harmful to health. Some of these plants have been designated as poisonous plants because of their effects in impacting biological functions in other organisms which are harmful [24]. They are therefore damaging to either the survival or the normal function of the individual. The dose received may be due to either acute (short) or chronic (long-term) exposure. However, in TM, plants with toxic constituents are known and are avoided or used cautiously in herbal product formulations. Even if these are employed in medicinal products, they are employed below toxic levels and hence, if at all, hardly result in

any fatality when administered by professional practitioners or experienced persons.

Generally, plants used in traditional medicines have been considered safe as a result of the long history of use in the treatment of diseases based on knowledge accumulated over several centuries. In many cultural settings, toxic fatalities have been rare due to systematic selection of medicinal plants for use. While thousands of people die each year from even supposedly 'safe' over-the-counter remedies, deaths or hospitalizations due to herbs are so rare that they are hard to find; not even the United States National Poison Control Centers have a category in

When used appropriately as dietary supplements, food supplements or medicines, traditional medicines are generally regarded as safe. However, there are instances where adverse events ascribed to herbal medicines used have been reported in both humans and animals. For example, Barbosa et al. [25] reported clinical and pathological neurological disorders in horses following a large intake of fresh *Bambusa vulgaris* leaves. Paradoxically, the aqueous decoction is a popular antimalarial medicine in Ghana [11, 21] and this has been used without any report of adverse reaction. Besides, the aqueous extract of the leaves did not cause cytotoxicity in normal human cells [11, 21]. In these situations, the dose of the constituents administered is of great importance; as stated by Paracelsus that, 'All substances are poisons; there is none, which is not a poison. The right dose differentiates a poison and a remedy' [26]. This is to say that the toxicity of any substance, including medicinal plants and even food, is largely dependent on the amount or dose used. A non-toxic substance can be toxic at a high dose, and a very toxic substance can be considered safe if the dose is low [27]. Over-dosage in the course of treatment is bound to pose safety problems. The dose-toxicity relationship was illustrated by the toxicity of *Bupleuri chinense* in which the toxic dose was about 21 times than the common clinical dose of 9 g/60 kg [28].

**8. Safety of medicinal plants and herbal medicines used in** 

**7. Medicinal plant use in therapy**

**traditional medicine**

their database for adverse reactions to herbs [17].

#### **5.1. Acute toxicity**

Acute toxicological studies investigate the toxic effects produced by a single large-dose exposure to a toxicant lasting no longer than 24 h. This may result in severe biological effects (harm or death) to the organism. The results of acute toxicity are not only important in the consideration of accidental poisoning with a chemical but also are used for the planning of chronic toxicological studies [15]. The development of tolerance is usually revealed by an acute exposure. The starting point for toxicological classification of chemicals uses the LD50 value, which is the dose administered in acute toxicity testing that causes death in 50% of experimental animals [16].
