The US Food and Drug Administration is recalling some medicines commonly used to help control blood pressure because batches of it may contain a chemical that’s used to induce cancer in lab rats.

The recall was issued after it was discovered that a manufacturing change at China’s Zhejiang Huahai Pharmaceutical Co. inadvertently exposed one ingredient, valsartan, to an organic chemical called N-nitrosodimethylamine (NDMA). That chemical is considered a probable carcinogen, and can be toxic for the liver and other organs. The recall applies to three companies: Major Pharmaceuticals, Solco Healthcare, and Teva Pharmaceuticals Industries Ltd. The agency is asking those companies to pull their valsartan medications from the market, which include tablets marked under the name “Valsartan,” but also tablets under brands such as Actavis, according to the FDA site.

“We have carefully assessed the valsartan-containing medications sold in the United States, and we’ve found that the valsartan sold by these specific companies does not meet our safety standards,” said the FDA’s Janet Woodcock, director of its Center for Drug Evaluation and Research in the agency’s press release.

There are well-documented reasons to be worried about NDMA, not least of all its use as a poison in a number of crimes. In 1978, a German chemistry teacher was convicted in a case (in German) in which he attempted to murder his wife by mixing NDMA into her blackberry jam. That same year, a man in Omaha, Nebraska was sentenced to death for using NDMA to spike the lemonade and kill a baby and a 24-year-old man at his girlfriend’s family function. And in 2013, a Chinese student at Sudan University was poisoned by his roommate with NDMA that had been slipped into his chilled water. He died 15 days later.

This recall is particularly complicated because use of drugs with valsartan is so widespread. The FDA’s drug- shortages team is working to find ways to ensure there will still be an adequate supply. The situation calls into question the safety and efficacy of drugs made overseas for the US market and the safety processes used by federal agencies. In an interview (paywall) with The New York Times, Cleveland Clinic cardiologist Harry Lever said it’s becoming harder for him to write prescriptions for patients, as it’s difficult to know what’s exactly in some of the drugs produced in places such as India and China.

In the US, Solco said (pdf) it is “notifying its distributors and customers by letter and email and is arranging for return of all recalled products.”