The antacid Zantac — known as ranitidine in generic form — is available over the counter or as a prescription. People can take the drug orally in pill and liquid form or intravenously as an injection.

GlaxoSmithKline first received FDA approval for Zantac in 1983, and by 1988 it was the world’s best-selling drug, bringing in $1 billion in annual sales.

Currently, Sanofi markets brand-name Zantac in the United States. In 2018, the company reported it made 113 million euros, the equivalent of roughly $124 million in the United States.

According to Bloomberg Intelligence, nearly 25 million prescriptions for ranitidine were written in 2018.

Zantac side effects are typically mild and pass quickly. The most commonly reported adverse events include constipation, diarrhea and nausea or vomiting. Rarely, some serious side effects such as skin rashes, liver failure and cardiac disorders may occur.

Ranitidine, the active ingredient in Zantac, belongs to a class of antacid drugs called H2 blockers, or histamine-2 receptor agonists.

H2 receptor agonists work by blocking histamine from parietal cells that line the stomach. This prevents the stimulation of the proton pump, an enzyme that transports hydrochloric acid secreted by the parietal cell. Inhibiting the proton pump reduces the amount of acid in the stomach, which, in turn, reduces symptoms of gastric disorders such as heartburn, GERD and gastric ulcers.

Zantac starts to work in as little as 30 minutes. It can control acid production for up to 12 hours and reduce the frequency and severity of heartburn.

Over-the-counter and prescription Zantac have different instructions for use. Depending on the reason for the health provider prescribing Zantac, the dosages will vary.

Hospitals use the Zantac injection for patients with pathological hypersecretory conditions or intractable duodenal ulcers, or as an alternative to the oral medication.

OTC Zantac treats heartburn with acid indigestion and sour stomach caused by eating or drinking certain foods or beverages. Children under 12 should not use Zantac without first getting approval from a health care provider.

Prescription Zantac treats several acid-related conditions, from GERD to erosive esophagitis.

Children as young as one month old may take the drug, but researchers have not studied it in children younger than one month and cannot make dosing recommendations.

Providers should adjust the dosage for people with impaired kidney function.

Tell your health care provider about all medications, herbal supplements and vitamins you take before taking Zantac. Avoid drinking alcohol with the drug because it may increase the risk of stomach damage.

Because ranitidine affects stomach acid, it may increase or decrease the effectiveness of drugs that rely on stomach acid to be effective.

There are no interactions listed for Zantac OTC, but the prescription drug label includes several.

Zantac works differently from Prilosec, which belongs in the proton pump inhibitor class. Deciding which type of drug to use depends on how bad the symptoms are and how often they occur.

Starting on Sept. 24, 2019, some manufacturers began voluntary Zantac recalls of certain lots of the drug because of contamination with N-nitrosodimethylamine, or NDMA — a chemical that may cause cancer.

The FDA had previously announced recalls of valsartan and blood pressure drugs losartan and irbesartan that had been contaminated with NDMA.

At first, the agency didn’t agree that NDMA levels present in ranitidine were too high. But after preliminary testing of some drug samples, on Oct. 2, 2019, the FDA stated that contamination levels were “unacceptable.”

On Nov. 1, 2019, the agency announced that it had found NDMA in all the drug samples it tested. It determined that “the levels of NDMA in ranitidine and nizatidine are similar to the levels you would expect to be exposed to if you ate common foods like grilled or smoked meats.”

The FDA set the daily acceptable limit for NDMA consumption at 96 nanograms — 0.32 parts per million, or ppm. It recommended that all manufacturers with levels above this limit recall their products.

Walmart, CVS, Walgreens and Rite Aid pulled all brand-name and generic Zantac from store shelves.

Then, on April 1, 2020, the FDA announced that its studies had revealed that NDMA in some ranitidine products increases over time and when stored at higher than room temperatures. As a result, the agency said, consumers could be exposed to unacceptable levels of NDMA.

The FDA requested an immediate market withdrawal of all ranitidine products. According to the agency, consumers taking OTC ranitidine should stop taking the drug, dispose of their supply properly and not buy more. Patients taking prescription ranitidine should speak with their doctor or other health care provider about alternatives.

Shortly after the first recalls, people began filing Zantac lawsuits and claimed the drug was responsible for causing cancer. Companies named in lawsuits include Zantac manufacturers Sanofi and Pfizer.

On Feb. 6, 2020, the United States Judicial Panel on Multidistrict Litigation consolidated 140 cases in MDL No. 2924 in the Southern District of Florida under U.S. District Judge Robin Rosenberg. Plaintiffs’ attorneys have predicted a large number of cases.

The lawsuits allege that manufacturers knew that ranitidine could form NDMA in the human body and increase cancer risk, but failed to inform consumers.