[Updated 2/24/21] This guidance recommends steps manufacturers of APIs and drug products should take to detect and prevent unacceptable levels of nitrosamine impurities in pharmaceutical products. The guidance also describes conditions that may introduce nitrosamine impurities. The recent unexpected finding of nitrosamine impurities, which are probable human carcinogens, in drugs such as angiotensin II receptor blockers (ARBs), ranitidine, nizatidine, and metformin, has made clear the need for a risk assessment strategy for potential nitrosamines in any pharmaceutical product at risk for their presence.