Dozens of medications used to treat high blood pressure have been recalled over the past several months as federal investigators discover potentially cancer-causing impurities in them. When American Health Packaging recalled one lot of valsartan pills on March 7, the Public Interest Research Group said it was the 75th recall of blood pressure medications since the problem first appeared.

These common prescription drugs include valsartan, losartan, and irbesartan in different combinations and from different manufacturers.

The problems have become so widespread that on March 12 the FDA prioritized approval of a new generic of valsartan to help relieve shortages of the drug. In April, the agency  released a list of 40 blood pressure medications it says are free from contamination. You can find the list here.

“Our goal is for this information to help health care providers as they consider acceptable treatment options for their patients,” the agency said in a statement.

The FDA is also working to determine what exactly has caused the impurities and what changes need to be made in the manufacturing process to prevent it. The Public Interest Research Group said in March that the FDA needs to step up the pace.

“After 75 recalls it is clear more aggressive action is needed,” PIRG consumer watchdog Adam Garber said in a release. “Americans expect their blood pressure medicadtion to treat their conditions, not cause cancer. The FDA needs to finish its investigation and develop a plan to prevent further contamination.”

Almost 60 million prescriptions were written for losartan drugs in 2016 and 14 million for valsartan or a drug that includes it. An additional 3.6 million prescriptions were written for irbesartan that year. Here’s what you need to know.

What blood pressure drugs have been recalled?

Valsartan. There have been so many types of valsartan recalled this year that the FDA has created a website listing just for them. The latest is American Health Packaging’s 160 mg valsartan tablets, lot number 179791 that expire on March 31, 2020. The pills come in 100-count blister packs with NDC number 60687-139-01.

Losartan. In December, the FDA announced a voluntary recall of losartan potassium tablets USP.  An addition eight lots of Torrent Pharmaceuticals’ losartan tablets were added to a previous recall in January. See which products were affected by the recall.

In November, the FDA announced a voluntary recall of losartan potassium/hydrochlorothiazide, 100 mg/25 mg tablets in 1,000-count plastic bottles, NDC 0781-5207-10, Lot number JB8912, Exp. Date 06/2020.

Torrent’s recall was expanded on Jan. 22 to include 10 additional lots of losartan potassium tablets, and six lots of losartan potassium and hydrochlorothiazide tablets. Torrent further expanded the recall in April for 36 more lots of losartan potassium tablets and 68 lots of losartan potassium/hydrochlorothiazide tablets. In September, Torrent announced that an additional three lots of losartan potassium tablets in 100 mg and 50 mg doses, and two lots of losartan potassium/hydrochlorothiazide tablets 50 mg/12.5 mg, and 100 mg/25 mg are being recalled as well. See the full list here.

Macleods Pharmaceuticals Limited on Feb. 25 recalled one lot of losartan potassium/hydrochlorothiazide combination tablets 100mg/25mg, with a July 2019 expiration date. Macleods on June 26 also recalled 32 lots of losartan potassium including two lots of 50 mg tablets and losartan potassium/hydrochlorothiazide tablets, including 12 lots of 50 mg/12.5 mg strength, three lots of 100 mg/12.5 mg and 15 lots of 100 mg/25 mg strength.

Camber Pharmaceuticals on Feb. 28 recalled 87 lots of losartan tablets USP 25mg, 50 mg and 100 mg. See the affected products and what the label looks like.

Legacy Pharmaceutical Packaging, LLC on March 15 recalled 43 lots of losartan tablets. On April 24, the company recalled an additional lot of 50mg losartan tablets. See a list of affected products here and here.

Teva Pharmaceuticals USA on April 26 recalled 35 lots of losartan potassium tablets (6 lots of 25 mg pills and 29 lots of 100 mg) that were sold exclusively to the Golden State Medical Supply of Camarillo, CA. Golden State re-packages the tablets under its own label for retail sale. Teva expanded this recall on June 10, 2019, with another six lots of losartan potassium USP tablets in 50mg and 100mg strength.  See all the affected products here.

Irbesartan. In July, the FDA announced a voluntary recall of irbesartan tablets. See which products were affected by the recall.  In January 2019, Prinston Pharmaceutical Inc., doing business as Solco Healthcare LLC, voluntarily recalled eight llots of irbersartan-based drugs. These are not yet listed on the FDA’s website of all recalled ibersartan products. The recall involves irbersartan and irbersartan HCTZ tabletes manufactured in China.

Why are the drugs being recalled?

In each case, a recalled drug was contaminated with N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA) or N-Nitroso N-Methyl 4-amino butyric acid (NMBA).

Thosechemicals are believed to cause cancer in humans. Research also suggests NDEA can cause liver and blood cell damage.

NDEA is used to make rocket fuel and can also be found in some food and drinking water, but at low levels. It can also be a created through certain chemical reactions and as a byproduct of industrial processes.

What is the risk of getting cancer from one of these drugs?

The FDA says it is very small. The amount of NDMA found in the recalled valsartan drugs exceeds acceptable levels. Records from drug manufacturers show the impurity may have been in the valsartan products for up to 4 years. The FDA estimates that if 8,000 people took the highest valsartan dose, which is 320 milligrams, from recalled batches every day for 4 years, there would likely only be one additional case of cancer over the life of those 8,000 people.

For context, 1 in 3 people in the United States will be diagnosed with cancer in their lifetime.

What’s driving the spike in recalls?

A common thread among all of these recalls is that the drugs, or ingredients in the drugs, were all made in China or India.

This globalization of the nation’s drug supply helps keep prices down, as it is cheaper to have them made in other countries. But with lower costs sometimes comes lower quality control.

What’s being done about products made in other countries?

An FDA spokesman says the agency is still investigating how these drugs became contaminated. Inspectors believe contaminated compounds were unintentionally created through a chemical reaction.

What should people who rely on these medicines do?

Experts say anyone taking a recalled drug should continue to do so, but contact your doctor or pharmacist immediately. The threat from the contamination may be less than the threat of not taking the drug.

Your doctor or pharmacist can help you find an alternative. But at least one expert says the recalls are making it more difficult to find valsartan drugs that have not been recalled. And, he says, some blood pressure drugs not on the recall list have seen price increases as demand spikes.