Tap Water May Be the Safest Choice for Enteric-Coated Medications, Study Finds
Key Insights
New research in Pharmaceutics shows that alkaline bottled water can prematurely dissolve enteric coatings on medications within minutes, potentially altering drug release and absorption.
Apple juice and other acidic beverages slowed drug release, while tap water maintained coating integrity for the majority of tested formulations.
Of 103 enteric-coated drug labels reviewed, only nine provided specific guidance on which beverage to use, highlighting a critical gap in patient instructions.
The beverage you use to swallow your pills may significantly influence how those medications behave in your body, according to new research published in the journal Pharmaceutics. The study found that alkaline bottled waters with high mineral content can cause the protective coating on enteric-coated medications (search) to break down prematurely, while tap water reliably maintained coating integrity for most formulations tested.
Dr. Adrienn Demeter, a student at the Faculty of Pharmaceutical Sciences of Semmelweis University and first author of the study, captured the clinical concern succinctly: "In the pharmacy, we regularly see that many patients are unaware of how much it matters what they take their medication with. This can also affect whether the treatment works as intended."
How Different Beverages Affect Drug Coatings
The research team examined how seven liquids—including tap water, filtered water, alkaline water, and apple juice—affected various enteric-coated medications (search) under laboratory conditions. They also analyzed 22 commonly consumed beverages, though less extensively than the seven tested in the lab.
Enteric coatings are polymer-based protective layers designed to shield active pharmaceutical ingredients from the stomach's acidic environment, ensuring that drug release occurs in the intestine where absorption can take place. These coatings are commonly used on anti-reflux medications, gastroprotective drugs, psychiatric medications, and anti-inflammatory pain relievers.
The findings were striking. Alkaline bottled waters with high mineral content caused the greatest changes to the pills' protective coating. In some cases, deterioration began after just five minutes. After 15 to 30 minutes of soaking, more than 90% of the active ingredient had been released prematurely.
Dr. Nikolett Kállai-Szabó, the study's lead author, explained the mechanism: "The small drug particle does not know whether it is already in the intestine or still sitting in a glass. If the pH of the surrounding environment is similar, the coating may begin to dissolve in the same way."
Conversely, more acidic beverages had the opposite effect. Apple juice showed almost no premature release of the active ingredient at the start of testing, suggesting the coating had remained largely intact under acidic conditions.
"When the products were tested in tap water, the majority of formulations maintained coating integrity," the study authors wrote.
A Gap in Labeling Guidance
The researchers also reviewed the Summary of Product Characteristics (SmPCs)—official, regulator-approved prescribing documents—for 103 enteric-coated drugs. The results revealed a significant information gap.
Of the 103 medications examined, 42 did not specify what liquid should be used to take the medication. Another 31 mentioned only "liquid," while 21 referred simply to "water" without further clarification. Just nine SmPCs provided specific guidance on what beverage to take or mix the medication with, such as apple juice or another mildly acidic liquid.
"Healthcare professionals generally assume that medications are swallowed with plain tap water, but that is not always obvious to patients today, given the wide variety of mineral and medicinal waters available on the market," said Dr. Kállai-Szabó.
Clinical Implications for Patients
The findings carry particular significance for patients who struggle to swallow pills. Past studies have found that approximately 40% of American adults have difficulty swallowing pills, with older adults and young children being especially affected. These patients often open capsules and mix the contents into liquids, yogurt, or applesauce—a practice that, combined with the wrong beverage choice, could further compromise the enteric coating.
The researchers stressed that their findings do not suggest mineral or medicinal waters are inherently problematic on their own. Rather, enteric-coated medications (search) appear to be best taken with plain tap water.
"Recommending slightly acidic or pH-neutral liquids and discouraging the use of alkalizing mineral waters may significantly reduce the risk of unintended premature drug release and improve patient safety," the study authors concluded.
Before opening a capsule or adjusting how a medication is taken, the research team emphasized that patients should consult a doctor or pharmacist.