Many are still readily available. Also, because medicinal herbs are not regulated for content or efficacy, it is impossible to know if they actually contain the advertised active ingredient, or other substances that may result in adverse effects. The possibility of adverse interactions is heightened by the fact that the potential for such is not described on package inserts for most prescription drugs, and that package inserts are not required for herbal remedies. While dose, manner and frequency of use of prescribed drugs are reviewed by prescribing physicians, herbal remedies are most often self-prescribed, and not subject to such control. Little is known about chronic toxicities that may be result from prolonged use.
Medicinal herbs contain a variety of chemicals, some of which are toxic at high doses.
Also, because such products cannot be patented, research funded by one company could easily be appropriated by another. Issues of standardization and stability were also explored in the JAMA and NEJM articles and at the recent international workshop. Some products are believed to achieve their beneficial effects through the synergistic working of several chemicals. While synthetic drugs are produced in highly purified form, medicinal herbs are typically gathered in the wild or grown in relatively small amounts. Active ingredients may vary significantly depending on many conditions of growth, harvesting, and processing.