The growing use of herbal medicines: issues relating to adverse reactions and challenges in monitoring safety
Toxicity and Adverse Health Effects of some Common Herbal Medicines
In most countries, herbal medicines and related products are introduced into the market without any mandatory safety or toxicological evaluation. Many of these countries also lack effective machinery to regulate manufacturing practices and quality standards. These herbal products are continuously made available to consumers without prescription in most cases and the potential hazards in an inferior product are hardly recognized (
Bandaranayake, 2006).
It is important to reiterate the staggering rate at which interest and use of herbal medicines is expanding. Over the past decade, the use of herbal medicines represents approximately 40% of all healthcare services delivered in China while the percentage of the population which has used herbal medicines at least once in Australia, Canada, USA, Belgium, and France is estimated at 48%, 70%, 42%, 38%, and 75%, respectively (
Foster et al., 2000;
WHO, 2002b). In spite of the positive perception of patients on the use of herbal medicines and alleged satisfaction with therapeutic outcomes coupled with their disappointment with conventional allopathic or orthodox medicines in terms of effectiveness and/or safety (
Huxtable, 1990;
Abbot and Ernst, 1997), the problem of safety of herbal remedies continues to remain a major issue of concern.
The general perception that herbal remedies or drugs are very safe and devoid of adverse effects is not only untrue, but also misleading. Herbs have been shown to be capable of producing a wide range of undesirable or adverse reactions some of which are capable of causing serious injuries, life-threatening conditions, and even death. Numerous and irrefutable cases of poisoning have been reported in the literature (
Vanherweghem and Degaute, 1998;
Cosyns et al., 1999;
Ernst, 2002). The toxicity evaluation of the polyherbal formula, Yoyo “Cleanser” Bitters®, conducted recently in our laboratory (
Ekor et al., 2010), was prompted by an unpublished case report of a young male adult who had been on self-medication with this herbal product and was subsequently admitted to the hospital on account of liver failure. Yoyo “Cleanser” Bitters® is one of the herbal remedies that is widely advertised in the various Nigerian media and as such has gained so much public acceptance over time and continues to enjoy increased patronage among consumers, especially in the southwestern part of the country. Our study revealed that this herbal formula was capable of elevating plasma levels of liver enzymes and inducing hypokalemia following 30 days administration in rats. From our observation, the potassium loss (which is capable of predisposing to dangerous arrhythmias) was a greater risk associated with this herb during this sub-acute exposure or toxicity study. Prior to this study, we had evaluated the safety of “super B blood purifier” and “super B seven keys to power” mixtures in experimental model over a decade ago (
John et al., 1997). These herbal mixtures were marketed by a registered Nigerian company which cultivated medicinal plants and manufactured medicinal herbal preparations. The herbal blood tonics were well patronized by common folks who claim their efficacy according to the manufacturer’s stipulation that “they are safe, give strength and cleanse the blood and body of infection.” We obtained the herbal constituents (
Entandrophragma utile and
Anacardium occidentalis) and investigated the individual plant extract as well as the herbal tonics made from them. Although, all the extracts and tonics proved safe during acute toxicity study, chronic toxicity testing revealed splenic enlargement in 10% of mice that received
E. utile or either of the two tonics and one case of lung tumor (
John et al., 1997). Recently,
Auerbach et al. (2012) reported an association between traditional herbal medicine use and the development of liver fibrosis among study participants in Uganda. A number of Chinese herbal medicines and other herbal medicines from different parts of the world have also been implicated in cases of poisoning. Many of them have been shown to contain toxic compounds which are capable of reacting with cellular macromolecules including DNA, causing cellular toxicity, and/or genotoxicity (
Rietjens et al., 2005). For the purpose of brevity and other obvious constraints, adverse reactions of only a few commonly used herbal medicines are described below.