If you read the Valisure petition to the FDA, it gives a lot more info. In a nutshell, they found that the molecules making up ranitidine are inherently unstable and especially so in the human body. The NDMA is therefore made as the drug lies around or once it is ingested. Previous tests by the US FDA and other government regulators have missed the NDMA due to not replicating this in tests. Even more worrying is that studies have shown for years that NDMA is excreted in urine in high amounts in people taking ranitidine and contaminate water.
I feel very angry and sad - my DC took this for months. Some people take this longer term.
There is nothing at of us can now do to undo harm but no wonder “big pharma” is no longer trusted. They produce drugs, and get to test them themselves and outsource their production and the whole thing is a snake fest.