The FDA declared a shortage of Adderall due to ongoing manufacturing delays, with some companies leaving backorders for pharmacies across the states.

Drew Angerer/Getty Images(CNN) - Drugmaker Novartis said it is halting distribution of all ranitidine medicines made by Sandoz, a measure it called "precautionary" after the acid-reducing medications were found to contain an impurity. The FDA is evaluating whether the low levels of NDMA in ranitidine pose a risk to patients and said it will share the information when it is available. In case of concerns, adequate additional measures will be implemented in alignment with relevant Health Authorities as required," Novartis said in an emailed statement. "The FDA reported that the levels of N-nitrosodimethylamine (NDMA) in ranitidine in preliminary tests barely exceed amounts found in common foods. The FDA has been investigating NDMA and other impurities in blood pressure and heart medicines known as ARBs since last year.