Prilosec was originally approved for use with a prescription in 1989. In 2003, manufacturer AstraZeneca got FDA approval to sell an over-the-counter version, Prilosec OTC.

Both Prilosec OTC and prescription Prilosec use the same active ingredient, known as omeprazole.

While Prilosec OTC is intended to treat symptoms of frequent heartburn, its prescription-strength version is intended for use only under medical supervision and in treatment of an acual, diagnosed disease – conditions like esophagitis, peptic ulcer disease, or gastroesophageal reflux disease.

The FDA notes that Prilosec OTC is recommended for treatment of frequent heartburn – heartburn that occurs two days or more per week.

It’s not recommended for heartburn that happens only occasionally, as it carries the risk of Prilosec OTC side effects.

Since it can take one to four days to take effect, it’s also not recommended for for persons seeking immediate relief from heartburn.

Prilosec OTC is one of a class of drugs called proton-pump inhibitors, or PPI inhibitors. These drugs work by reducing the production of acid in the stomach. Lower levels of stomach acid generally translate to reduced symptoms of heartburn. Prilosec OTC is the first of these drugs to be made available without a prescription.

Since it became available, Prilosec has been extremely popular. It’s estimated over 27 million people have taken Prilosec OTC to treat heartburn.

Keeping Tabs on Prilosec OTC Side Effects

But use of Prilosec, especially in the long term, comes with a risk of developing certain Prilosec OTC side effects. Prilosec and other PPIs have been linked to development of conditions as serious as heart attacks, kidney problems and dementia.

Heart Attacks

A study by researchers from Stanford University suggests that Prilosec OTC side effects may include an increased risk of heart attack. Researchers reviewed the records of millions of patients and found that myocardial infarction occurred 16 percent more frequently in patients who took PPIs.

The researchers noted that patients who took a different kind of acid-reduction medication known as H2 receptor blockers did not show a similar increase in heart attack rates.

Kidney Problems

A study published in April 2015 found a connection between use of PPIs like Prilosec and kidney injury in older patients. Researchers found older patients who took PPIs developed kidney injury at more than twice the rate of others who did not use PPIs.

Another study published this year found persons who took PPIs like Prilosec could face a 28 percent greater risk of kidney disease. The study tracked thousands of PPI users over a five-year period.

For comparison, the study also tracked users H2 receptor blockers. They found that users of PPIs developed kidney disease at a notably higher rate than those who used H2 receptor blockers.

Kidney injury and kidney failure can prevent the kidneys from doing their job of filtering metabolic wastes out of the blood. In their more advanced stages, patients may require dialysis or a kidney transplant.

Dementia

More recent research suggests Prilosec OTC side effects could even include development of dementia. In a study published in February 2016, researchers in Europe reviewed the histories of tens of thousands of individuals who developed dementia, some of whom were regular PPI users and others of whom were not.

The researchers found that over a seven-year period, those who took PPIs had a 44 percent higher risk of developing dementia.