Millions of people suffer from heartburn every single day, causing great discomfort and impacting what they can and can't eat.

Heartburn drugs are designed to relieve these symptoms, but now researchers believe they may come with their own risks.

Proton-pump inhibitors, otherwise known as PPIs, are some of the world's most widely prescribed drugs on the market. However, a new study of medical records has found that they may also significantly increase the risk for heart attack.

However, researchers found that the second most prescribed type of drug for heartburn, H2 blockers, did not increase the risk of heart attack, highlighting the difference in the way these drugs work compared to PPIs.

"The association we found with PPI use and increased chances of a subsequent heart attack doesn't in and of itself prove causation," says Nigam Shah, lead author of a new study published this week and assistant professor of biomedical informatics and assistant director of the Stanford Center for Biomedical Informatics Research.

For the study, researchers examined nearly 3 million medical records for heartburn treatment, with roughly 300,000 patient records qualifying. In these patients, the rate of heart attack for people taking PPIs was compared to the rate among heartburn patients not taking PPIs. The results showed a 16 to 21 percent increased chance of heart attack among those using PPIs.

Previous research has shown that PPIs reduce the level of nitric oxide in endothelial tissue, which according to Shah means anybody using the drugs could be more at risk of having a heart attack.

"We looked at cardiovascular risk for different PPI drugs," Shah says. "And we found that the degree to which the use of any particular PPI was associated with a subsequent heart attack mirrors the degree to which the drug inhibits nitric oxide in the vasculature."

The authors of the study were quick to point out that people should not immediately stop taking their PPIs, however, as more research is needed into both PPIs and H2 blockers to determine their effects on the vascular system.

"This association needs to be tested in a large, prospective, randomized trial," said Dr. Nicholas Leeper, the study's senior author and an assistant professor of vascular surgery and of cardiovascular medicine. "The truth will come out when we randomize several hundred people, give half of them PPIs and put the other half on H2 blockers and see what happens."

This latest study on PPIs was published in the journal PLOS ONE.