This article describes three patients who developed factitious thyrotoxicosis, as well as other adverse effects, after taking herbal dietary supplements for weight reduction. All products were found to contain undeclared animal thyroid tissue and western pharmaceuticals causing the adverse effects. Adulteration is concealed addition of undeclared drugs, or other substances with therapeutic effects, to a health product. Consumption of such products, and the concealed components unwittingly, is obviously dangerous. Multiple adulterants in one product are often seen. Untoward adverse effect or drug interaction could occur. Overdose subsequent to poor standardization of the adulterants is another concern. Health care professionals must therefore be aware of the potential dangers posed by adulterated dietary supplements.