First it was blood pressure medication. Now FDA eyes more drugs for cancer-causing chemical.

For people managing high blood pressure, recalls of the carcinogen-tainted drug quinapril might sound familiar.

Since 2018, more than 12 million bottles of blood pressure-lowering drugs such as valsartan and losartan have been removed from the market because they contained cancer-risk chemicals called nitrosamines.

The same family of contaminants triggered recalls of the heartburn drug Zantac, the diabetes drug metformin and the smoking cessation medication Chantix.

The flurry of drug recalls because of carcinogens has prompted the Food and Drug Administration to assess the scope of the problem.

The federal regulator has asked drugmakers to evaluate all products for any risk they might contain nitrosamines. Companies that identify any such risk must conduct follow-up testing, report changes and take action by October.

DRUG RECALLS: Full list of FDA recalls since 2012

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What are nitrosamines?

Nitrosamines are found in water, cured and grilled meats, dairy products and vegetables, according to the FDA. While nearly everyone is exposed to trace amounts of nitrosamines, studies link the contaminants to increased cancer risk if people are exposed to large amounts over long periods of time.

Public health experts have long been aware of the small risk associated with sustained exposure to these contaminants.

Food safety experts have worked to reduce nitrosamines in food such as cured meats to far below levels found in the 1970s and 1980s, said Dr. Stephen Hecht, a University of Minnesota professor of cancer prevention.

"The difference is with drugs it's totally avoidable," Hecht said. "I don't think this could have happened in the 1970s because there was much greater awareness of the consequences."

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What to do if your prescription drug is recalled

The FDA has said the risk for anyone exposed to nitrosamines in drugs is small.

The agency has set acceptable limits on six types of nitrosamines, which equal up to one case of cancer per 100,000 people exposed to the contaminant.

Some recalled drugs have exceeded that amount. For every 8,000 people on the highest dose of valsartan for four years, FDA scientists concluded there would be one more cancer case above average rates for that population. Europe's drug regulator, the European Medicines Agency, estimated the risk to be one cancer case for every 3,000 patients.

As with the valsartan and losartan recalls in 2018 and 2019, the FDA has advised people on recalled quinapril to continue the medication until their doctor or pharmacist can identify a replacement.

Dr. Yul Ejnes, a clinical professor of medicine at Alpert Medical School of Brown University, said people might panic and immediately stop their medication when they hear about a recall. For a patient on a blood-pressure-lowering drug to manage conditions such as heart failure, halting the drug can create an immediate medical problem.

He generally recommends people call their pharmacist, who can check whether their drug is part of the recall. If it is, the pharmacist might be able to locate the same version of the drug that's not part of the recall. Or the pharmacist and doctor can find a substitute drug.

"The key message is it's a small risk; there's no imminent danger," said Ejnes, chair of the American Board of Internal Medicine. "There's no need to stop the drug. Now, we can find replacements."

What's being done to protect consumers?

Though the FDA said the risk is small for people who ingested these drugs, lawyers have filed thousands of lawsuits in state and federal courts on behalf of people who say they have been harmed.

In 2019, heartburn drug Zantac was removed from store shelves after the FDA found unacceptable levels of a nitrosamine called NDMA, or nitrosodimethylamine, in brand and generic versions.

In December, a Florida federal judge dismissed thousands of claims that alleged Zantac caused cancer. The judge ruled that the plaintiffs' experts did not use reliable methods linking the drug to cancer.

More than 1,000 claims against valsartan manufacturers are pending in federal court.

Meanwhile, FDA officials said the agency expects drug manufacturers who have identified a potential risk to complete testing and report changes they've made by Oct. 1.

"We continue to closely evaluate this type of impurity and will continue to investigate and monitor the marketplace and manufacturing efforts to help ensure the availability of safe, quality products for U.S. consumers," said FDA spokesman Jeremy Kahn.

Makers of generic drugs, which produce about 9 of 10 prescription drugs dispensed in the United States, have pushed back on the FDA's required comprehensive review. The generic drug's industry group, the Association for Accessible Medicines, said in a position paper that to review every drug would be a "Herculean task" that would divert resources and focus and could exacerbate drug shortages.

Instead, the organization wants to conduct a more efficient "risk-based" review that looks for the source of such impurities across all facets of drugmaking.

Why are we seeing so many contaminated drugs?

Independent experts say the recent recalls are partly the result of a system that values inexpensive manufacturing over drug quality.

David Light is CEO and co-founder of Valisure, an independent lab that first discovered Zantac and its generic versions contained nitrosamines. His lab's testing led to the voluntary nationwide recall of the medication for supermarket and drug stores. Since then, his lab has flagged potential harmful contaminants in consumer products such as hand sanitizers and sunscreens.

Though the FDA sets standards for drug companies to follow, it's up to the drug manufacturers to ensure their products are safe and free from impurities. This regulatory approach is an "honor system," Light said, adding that "some manufacturers are going to do a better job than others."

Generic drug manufacturers want to make inexpensive products and seek to control manufacturing costs. Insurers and consumers expect to pay less for generic medications.

"The fact that we have a broken market system where we're only valuing price and just assuming quality certainly increases the risk for these kinds of issues to crop up," Light said.

See a list of the latest food and drug recalls from the FDA here.

Ken Alltucker is on Twitter at @kalltucker, or can be emailed at alltuck@usatoday.com

This article originally appeared on USA TODAY: FDA eyes drugs with cancer-causing nitrosamines. What you should know.