The United States Food and Drug Administration requested manufacturers immediately withdraw all prescription and over-the-counter ranitidine (Zantac) products from the U.S. market due to a carcinogenic contaminant N-Nitrosodimethylamine (NDMA). Reviews of studies indicate that NDMA levels in ranitidine increase over time and when stored at higher than room temperature, resulting in exposure to unacceptable levels of the carcinogen. As a result of the withdrawal request, ranitidine products are no longer available for sale in the U.S.