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.

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.

Side effects information for Zantac comes from clinical trials and postmarketing reports from real-world clinical practice. A search for generic ranitidine and brand name Zantac at different dosages in the FDA Adverse Event Reporting System (FAERS) from 1982 to June, 20 2019 revealed 54,608 adverse event reports.

Overall, reports of adverse event appear to be limited. In 2017, there were over 15 million prescriptions for ranitidine, according to U.S. government reports, but only 1,958 adverse events reported in FAERS.

The most commonly reported side effects in FAERS are headache, diarrhea, nausea, indigestion, vomiting, dizziness, abdominal pain, pruritus (itchy skin) and trouble breathing.

According to the drug’s insert, serious Zantac side effects are rare. Of the total 54,608 adverse-event reports, serious events accounted for 22,995. These include 2,175 deaths.

If you suffer any of the following side effects, talk to your health care provider.

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 to the proton pump inhibitor class. Deciding which type of drug to use depends on the severity and frequency of the symptoms.

Starting on Sept. 24, 2019, some manufacturers of ranitidine began voluntary recalls of certain lots of the drug because of contamination with N-nitrosodimethylamine (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 it announced that contamination levels were “unacceptable.”

Generic Zantac makers Sandoz and Apotex recalled certain lots of their drugs in September 2019.

Sanofi, the maker of Zantac in the United States, initially did not recall the drug.

But on Oct. 18, 2019, the company announced a voluntary recall, issuing a press release that stated, “This recall is being taken due to possible contamination with a nitrosamine impurity called N-nitrosodimethylamine (NDMA). The company is working with health authorities to determine the level and extent of the recall.”

Walmart, CVS, Walgreens and Rite Aid have pulled all brand-name and generic Zantac from store shelves. The agency doesn’t have enough information to recommend not using ranitidine. But it recommended that concerned people use alternatives and talk to their doctors.

Dr. Reddy’s Laboratories Ltd. issued a recall on Oct. 1, 2019, for its ranitidine products marketed under several store brands, including Sam’s Club, Walgreens, Walmart, Kroger, CVS, CDMA, Dr. Reddy’s, HCA, Target, Thirty Madison and GeriCare.

Perrigo Company plc conducted tests of its ranitidine-based products that contained ranitidine active ingredients, called APIs, from external sources. On October 8, it halted shipments, and then on Oct. 23, 2019, it issued a recall.

After the recalls were announced, people who had been diagnosed with cancer after taking Zantac filed lawsuits against Sanofi.