Consumers are being warned to visually inspect medications bought over the counter.

For those who purchased bottles of Excedrin, Bufferin, NoDoz and Gas-X, produced by Novartis, they are being told to discard or return the products in a voluntary recall that started Sunday.

“Due to problems that occurred when these products were packaged and labeled at the site, it’s possible that tablets from one product may have been retained in the packaging machinery and then may have carried over into the packaging of another product,” said Dr. Edward Cox, director of the Office of Antimicrobial Products, Office of New Drugs, Center for Drug Evaluation of Research for the FDA.