Learning curves for bronchoscopy and simulation.

418 © Royal College of Physicians, 2013. All rights reserved. are used alone or co-administered with conventional drugs. Most herbal products on the market today have not been subjected to the approval process of the US Food and Drugs Association (FDA) and are not regulated for purity and potency. They may contain toxic substances or other contaminants which may increase the possibility of adverse effects.2 Hence rigorous scientific methodologies and clinical trials to ensure the quality and consistency of herbal products should be undertaken.