Online pharmacy Valisure reported that its tests showed high levels of a probable cancer-causing impurity in diabetes drug metformin.
High levels of N-nitrosodimethylamine (NDMA) were found in metformin made by 11 companies, including Amneal Pharmaceuticals and Aurobindo Pharma, the company said in a statement.
Valisure said it had requested the US Food and Drug Administration (FDA) to recall the identified lots of medicines.
The FDA declined to comment, saying it would respond directly to the citizen petition filed by the company.
The agency in December started an investigation into metformin for possible contamination and said earlier this year that it did not recommend a drug recall.
Amneal and Aurobindo Pharma did not immediately respond to a request for comment.
NDMA contamination was responsible for the recall of heartburn drug Zantac sold by Sanofi SA and some generic versions of the treatment last year.