Do Protein Pump Inhibitors Increase Cancer Risk?
How proper analysis of electronic medical records can help disentangle medication effects from symptom-driven treatment decisions.
A patient comes to the clinic with upper abdominal discomfort: reflux, burning, indigestion, nausea, pain after eating.
Modern medicine provides highly effective medications for relieving these symptoms: proton pump inhibitors (PPIs), which are medications that suppress gastric acid secretion (omeprazole, lansoprazole, and esomeprazole...).
Over the past decade, however, a growing number of observational studies have reported that upper gastrointestinal cancers, including stomach and esophageal cancers, are substantially more common among long-term PPI users.
Such a risk is biologically plausible and should not be dismissed lightly. Chronic acid suppression can alter stomach physiology, increase gastrin levels, and change the gastric microbiome in ways that could potentially increase cancer risk.
This creates a real dilemma for treating physicians. Should they prescribe medications that effectively relieve patients’ symptoms, or avoid a treatment that could contribute to future cancer risk?
To answer this question properly, it is crucial to separate the effects associated with PPI use from the symptoms and underlying conditions for which these medications are prescribed.
Upper gastrointestinal cancers often begin with vague symptoms such as reflux, gastritis, abdominal pain, nausea, and indigestion, precisely the symptoms for which PPIs are prescribed. This creates a major epidemiologic challenge known as reverse causation, where medications may appear associated with cancer, not because they cause cancer, but because underlying pathologic processes caused the symptoms that led to the treatment.
Notably, patients receiving PPIs have higher prevalence of gastrointestinal disease, smoking, alcohol exposure, obesity, and Helicobacter pylori infection, all of which may independently contribute to cancer risk.
So how can we separate the effect of the medication from the effect of the symptoms and diseases that caused patients to take the medications?
To address this question, we analyzed longitudinal electronic health records from our health system, identifying 875 patients diagnosed with upper gastrointestinal cancers during the last two decades and matching them to 8,750 similar control individuals who had not been diagnosed with cancer.
When we initially examined PPI exposure through pharmacy records during the 5 years preceding diagnosis, we were able to reproduce the concerning associations reported by earlier studies. Patients exposed to the major classes of PPIs had substantially higher rates of upper gastrointestinal cancer, with stronger associations observed for medication with more effective acid suppression: approximately a 2.4-fold increase for omeprazole and a 4-fold increase for esomeprazole.
But then we performed a more refined analysis.
Instead of analyzing the entire 5-year exposure period as a single variable, we divided the years preceding diagnosis into multiple smaller intervals and incorporated them simultaneously into a multivariable regression model.
This approach allows to estimate the independent contribution of medication exposure during each specific time window
The results revealed a striking temporal pattern.
The strongest apparent associations between PPIs and cancer occurred immediately before diagnosis, precisely during the period when early cancers are most likely to produce severe symptoms for which patients take treatment.
For example:
esomeprazole exposure during the final months before diagnosis was associated with a 7.7-fold increase in risk,
omeprazole exposure with a 3.8-fold increase,
lansoprazole exposure with a 3.5-fold increase.
However, when exposure occurred further from diagnosis, the signal changed dramatically. Exposure occurring 1-2 years, 2-3 years, and especially 3-10 years before diagnosis shifted toward neutral or even reduced risk. If PPIs were truly driving cancer development, one would expect longer and earlier exposure to be associated with progressively higher risk.
The pattern became even clearer after integrating gastrointestinal diagnoses into the analysis.
The strongest associations with future cancer risk were not linked to the medications themselves, but to the clinical conditions for which the medications were prescribed: peptic ulcer disease, abdominal pain, Gastro-esophageal reflux disease (GERD), gastritis, alcohol use, and Helicobacter pylori infection.
Moreover, once we excluded the periods immediately preceding diagnosis (where medication exposure is most likely to reflect new onset of symptoms), PPI exposure was no longer associated with increased cancer risk, and was instead associated with reduced risk.
These findings suggest that much of the alarming associations reported in earlier observational studies reflected symptoms experienced by patients who took these medications rather than harmful effects of the medications themselves. In fact, by reducing excess acidity and chronic inflammation, these medications may even reduce long-term cancer risk by limiting chronic tissue damage.
The broader lesson extends beyond PPIs. Large healthcare databases are powerful scientific tools, but interpreting them correctly requires careful attention to timing, disease progression, clinical context, and epidemiologic bias.
Using appropriate methodology, our study provides reassuring evidence that appropriately used PPIs are unlikely to be major long-term drivers of upper gastrointestinal cancer risk.
At the same time, the findings contain an important clinical warning: physicians should not ignore persistent or newly appearing upper gastrointestinal symptoms simply because acid suppression relieves them.
Sometimes the medication is not the danger.
Sometimes the symptoms themselves are a signal that should not be ignored.
References:
Association between proton pump inhibitor use and upper gastrointestinal cancer: A matched case-control study accounting for reverse causation and confounding by indication.
Sawaid IO, Din Z, Golan E, Ruppin E, Golan-Cohen A, Green I, Merzon E, Vinker S, Samson AO, Israel A.
PLoS Medicine 2026;23(1).
doi:10.1371/journal.pmed.1004842Context matters: Causality and global epidemiology of proton pump inhibitor safety.
Okabayashi S, Kaplan GG.
PLoS Medicine 2026;23(1).
doi:10.1371/journal.pmed.1004862
What an important study! Well done.