Histamine H2-receptor antagonists, also known as H2-blockers, are used to treat duodenal ulcers and prevent their return. They are also used to treat gastric ulcers and for some conditions, such as Zollinger-Ellison disease, in which the stomach produces too much acid.
N-nitrosodimethylamine, or NDMA, is a yellow, odorless liquid chemical once used to make rocket fuel. It is also a byproduct of several manufacturing processes and water chlorination. Small amounts of NDMA may occur in water, soil and air. It's been classified as a probable human carcinogen.