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July 27, 2026
Marianne Waldenfels
Coffee, milk, grapefruit juice, or highly alkaline mineral water: Some drinks can interfere with certain medications. Here's which combinations to avoid—and why plain water remains the safest choice.
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Coffee, a glass of milk, or mineral water – most people simply swallow their medication with whatever drink is close at hand. But not every drink is equally suitable. Some can influence how well a medication is absorbed by the body or how quickly it takes effect.
While grapefruit juice has long been known to cause interactions, a new study now suggests that highly alkaline mineral water could also be problematic with certain tablets.
Alkaline mineral water has been trending for several years. Unlike ordinary mineral or tap water, it has a particularly high pH value – usually above 8 – and is frequently marketed with promises of better recovery or a balancedacid-base balance. However, these claimed health benefits have so far barely been backed by scientific evidence.
Researchers at Semmelweis University in Budapest have now investigated whether highly alkaline mineral water could affect the efficacy of certain medications.
The study focused on so-called enteric-coated tablets. These have a special protective coating that prevents the active ingredient from dissolving in the acidic environment of the stomach, so the medication is released only once it reaches the small intestine. This group includes many proton pump inhibitors, such as omeprazole and pantoprazole, as well as some acetylsalicylic acid preparations (aspirin).
For thelaboratory study, the scientists placed various enteric-coated tablets in tap water, filtered water, apple juice, and several alkaline mineral waters with different pH values. The results showed that highly alkaline waters in particular attacked the protective coating significantly faster than the other drinks. With one of the tested medicinal waters, more than 90 percent of the active ingredient was released within five minutes.
The researchers emphasize, however, that this was a purely laboratory-based study. Whether the same effect occurs to the same extent in the human body has not yet been investigated.
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Interactions between grapefruit juice and medications have been far more thoroughly studied. Certain compounds in grapefruit inhibit the enzyme CYP3A4 in theintestine, which is responsible for breaking down numerous medications. As a result, some medications can have a significantly stronger effect than intended, and the risk of side effects increases accordingly.
Certain cholesterol-lowering drugs (statins), some blood pressure medications, immunosuppressants, and various psychiatric medications can all be affected. Because the effect of grapefruit juice can last for many hours,expertsgenerally advise avoiding grapefruit altogether when taking the relevant medications.
Even a single glass of grapefruit juice can be enough to alter the breakdown of certain medications. Depending on the drug, the effect can last for more than 24 hours.
The issue is not the milk itself, but its high calcium content.Calciumcan bind to certain active ingredients in the intestine and form poorly soluble compounds. The result: the medication is absorbed less effectively and may work less reliably.
This effect is particularlywell documentedfor antibiotics from the tetracycline group (such as doxycycline) and fluoroquinolones (such as ciprofloxacin or levofloxacin). Some osteoporosis medications known as bisphosphonates should also not be taken together with milk or other calcium-rich foods.
For this reason, prescribing information recommends leaving a time gap between taking these medications and consuming milk, yogurt, or calcium supplements – usually at least two hours, depending on the medication.
For many people, the first cup ofcoffeeis part of the morning routine – and is often taken alongside medication. But this too can be problematic.
This effect has been particularly well studied with levothyroxine, used to treat an underactive thyroid. Coffee can significantly reduce the absorption of the active ingredient in the intestine. Experts therefore recommend taking the medication in the morning on an empty stomach with a glass of water and waiting at least 30 to 60 minutes before having coffee.
Iron supplements and bisphosphonates for the treatment of osteoporosis should also not be taken together with coffee, as it can impair the absorption of their active ingredients. Professional societies and manufacturers therefore recommend taking these medications on an empty stomach with a glass of water and then waiting at least 30 minutes before drinking coffee – and even longer for some preparations.
Alcohol can also alter the effects of medications. Especiallyproblematicis the combination with sleeping pills, sedatives, opioids, or certainantidepressants. Alcohol can intensify their sedative effects, increasing the risk of drowsiness, dizziness, or even breathing difficulties.
Alcohol should also be strictly avoided when taking certain antibiotics, such as metronidazole.
Doctors and pharmacists recommend taking most medications with a large glass of tap water or still mineral water. Neither affects the absorption of most active ingredients, making them the safest choice.
