It is somewhat unusual for an OTC drug to be withdrawn from the market as a result of safety concerns, rather than market forces, though it does happen occasionally. For example, phenylpropanolamine was removed from sale in the United States over concern regarding strokes in young women. A study has been done examining consumer's perceptions about the risk of and access to nonprescription medication. The study concluded that a small percentage of consumers prefer having access to medication over potential risks of taking non-prescribed medication. Ranitidine was withdrawn from multiple markets due to concerns over the carcinogen "N"-nitrosodimethylamine (NDMA).