BEIJING -- Two Chinese herbal medicine manufacturers have been ordered to suspend production for allegedly treating drug ingredients with excessive sulfur, China's drug watchdog revealed Friday.

Baoshantang Pharmaceutical Co., Ltd. and Yingkang Pharmaceutical Co., Ltd., based in Guangdong and Guangxi provinces, respectively, have been told to suspend production and stop the distribution of relevant drugs, according to a circular issued by the China Food and Drug Administration (CFDA).

Authorities have already taken affected products off the market, according to the circular.

Some growers fumigate with sulfur to dry some herbal medicine components. However, high amounts of sulfur, which some drug manufacturers use to beautify or lengthen the shelf life of herbal medicines, have been detected, according the administration.

Sulfur dioxide residue is created during the process of fumigating or steaming, and long-term exposure to high amounts of sulfur dioxide can cause damage to the human body, especially the respiratory and digestive systems.

In order to curb the excessive use of sulfur, the administration will standardize the cultivation of herbal medicine materials and offer better training for growers, according to the circular.