USP Quality Review

No. 65, Issued 04/99

Developing Standards Monographs

“USP” (United States Pharmacopeia) or “NF” (National Formulary) monographs are established to ensure the purity and potency of products that are represented as conforming to the specifications. Plants and herbs, by their nature, are not uniform products. They contain numerous different chemical components, of which many may have biological activity after human ingestion. Botanical products may exert their effect through a combined, synergistic action of active constituents. The chemical complexity of botanicals makes identification of the “active” compounds a prodigious task. In fact, a component classically assumed to produce the “therapeutic” action of a botanical may not be the primary contributor to the effect. Difficulties in the determination of the elements responsible for biological activity have necessitated the practice of identifying “marker compounds.”

Marker compounds are chemicals believed by experts to be particular to a botanical and believed to participate in its “health benefit.” Therefore, even when the active ingredients have not been completely elucidated it is possible to perform analysis on a sample of the substance and set standards criteria. USP has been instrumental in establishing consensus among researchers on the designation of these markers. 

Proper identification of the plants and herbs themselves is essential. The entire specimen, from roots to seeds, must often be used to distinguish between botanical species or varieties. It is possible that similar plants may have overlapping marker compounds, yet differ in other, as yet unidentified, biologically active components. 

There are even differences among botanicals that are of the same variety. The environment where the plant is grown can vastly affect the chemical quality of a plant. Soil conditions, climate, and time of harvest all may alter the potency of a plant's, “medicinal” properties. The part of the botanical from which dietary supplements are produced can contribute to diversity among products. Manufacturers use various combinations of the leaves, stems, roots, and other plant parts. A botanical's active components may concentrate in a specific location within the plant. Some parts may not contain “therapeutically” beneficial elements at all. Although DSHEA legislation requires botanicals used as dietary supplements to identify the part of the plant from which the product is made, manufacturers are not limited to which parts they may choose to include. 

Dosage formulations are also left to the manufacturer's discretion. The content and potency of botanical products may vary greatly depending upon the formulation. Some products are distributed in traditional “drug-like” formulations, while others are marketed as teas. It is difficult to control the amount of dietary supplement delivered by a tea preparation because brewing times are likely to be dissimilar. Most botanical products do not have an established “dose” used for a particular effect. Different manufacturers may produce similar product formulations with widely variable amounts of “active” ingredients.

Contamination is an issue for botanical agents. Products that are collected from wild sources have the potential of being tainted by radioactivity or heavy metals. There is also the possibility that extraneous matter, such as “poisonous plants,” may grow around and be harvested with the desired botanical. Both wild and cultivated botanicals may have pesticide residues. Additionally, microbial and parasitic infestation may be present.

Development of standards for botanicals is fundamentally complex, as evidenced by the aforementioned reasons. There are also difficulties in designating assay methods that are feasible for the producers of botanical products to conduct without prohibitive cost. It is not unusual for compounds extracted from plant sources to be extremely volatile, literally disappearing before analysis can be performed.