WASHINGTON – The popular heartburn drugs Prilosec and Nexium don’t appear to spur heart problems, preliminary U.S. and Canadian probes announced Thursday.

The Food and Drug Administration and its Canadian counterpart began reviewing the drugs, used by tens of millions of people, back in May, when manufacturer AstraZeneca provided them an early analysis of two small studies that suggested the possibility of a risk.

Those studies compared treating the chronic heartburn known as gastroesophageal reflux disease, or GERD, with either of the two drugs or with surgery and tracked patients for five to 14 years. The company’s initial analysis counted more patients treated with drugs who had had heart attacks, heart failure or heart-related sudden death.

The FDA followed up on those studies and found that they seemed skewed: Patients who underwent surgery were younger and healthier than those treated by drugs, suggesting the heart link was a coincidence.

While the studies’ designs make safety assessments difficult, many of the participants who developed heart problems had risk factors before starting the drugs, Health Canada said Thursday.

The FDA then looked at 14 additional studies of the drugs and found no evidence of heart risks. In fact, in a few studies where patients received either medication or a dummy pill, those who took the heartburn drugs actually had a lower incidence of heart problems.

The FDA plans to complete its probe within three months, but issued a public notice Thursday that it “does not believe that health care providers or patients should change either their prescribing practices or their use of these products at this time.”

Health Canada reached the same initial conclusion. It also urged doctors and patients to make no changes until its own probe is finished by year’s end, noting that untreated GERD can lead to serious complications.