For millions of Americans, starting the day with a cup of coffee feels harmless—even healthy. But new research suggests that caffeine, the key stimulant in coffee, tea, and energy drinks, could interfere with the effectiveness of one of the most widely prescribed antibiotics.
An international team of scientists recently tested 94 different substances to see how they interacted with E. coli, a common bacteria responsible for more than 250,000 infections in the U.S. each year. They discovered that caffeine significantly reduced the ability of ciprofloxacin (Cipro)—a frontline antibiotic used to treat urinary tract, skin, and respiratory infections—to kill E. coli. The reason? Caffeine activates a genetic regulator called Rob, which alters transport proteins inside the bacteria. This change blocks Cipro from entering the bacterial cells, making the drug less effective.
This is alarming given the scale: roughly two-thirds of Americans drink coffee daily, while nearly four million Cipro prescriptions are filled every year. If caffeine truly reduces the drug’s impact, it could contribute to the growing global threat of antibiotic resistance—when bacteria evolve to survive treatments that once killed them. In severe cases, resistance can render infections untreatable, raising the risk of hospitalization or death.
While most E. coli infections cause temporary cramps, diarrhea, and nausea, some lead to hemolytic uremic syndrome, a dangerous kidney complication. Each year, the CDC estimates 265,000 Americans fall ill, with more than 3,000 requiring hospital care and about 61 dying.
The researchers caution that their study was conducted in lab cell samples, not humans, so more testing is needed to confirm real-world effects. Still, the findings highlight an urgent need to study how everyday habits—like that daily cup of coffee—may unintentionally undermine lifesaving medicine.
