According to the FDA, NDMA is an impurity. In other words, Zantac is contaminated. Either its original ingredients are tainted. Or it the NDMA creeps in in during the manufacturing process. But according to Valisure (an online pharmacy), NDMA is not an impurity. Instead, it is a byproduct. Valisure claims that Zantac causes NDMA to manifest in the body during the digestion process when the active ingredient breaks down.The FDA responded that Valisure's methods of simulating human digestion were unrealistic. This is because Valisure exposed the ranitidine to unnaturally high heat (130 degrees Fahrenheit). And Valisure added more nitrates than a typical person would ingest. However, Valisure claims it also detected NDMA when in only 37 degrees heat and with typical amounts of nitrates (like those in process meats). The FDA has yet to reveal how much NDMA it found using Valisure's methods.Either way, Zantac users are likely ingesting far more NDMA that what the FDA says is safe.