El Paso, United States - August 06, 2025 A new study from The University of Texas at El Paso reveals striking video evidence showing how caffeine consumed at night causes fruit flies to behave recklessly. Led by biologists Erick Saldes, Paul Sabandal, and Kyung-An Han, the research focused on how nighttime caffeine affects inhibition and impulsivity in fruit flies, a species commonly used to study complex behaviors due to their genetic similarities to humans. The study showed that fruit flies exposed to caffeine at night failed to suppress their movement when faced with strong airflow, a natural deterrent. Instead, they flew recklessly, ignoring the unpleasant stimulus. “Under normal circumstances, flies stop moving when exposed to strong airflow,” said Saldes. “Flies consuming caffeine at night showed reckless flying and failed to suppress movement despite the unpleasant stimulus.” Interestingly, fruit flies given caffeine during the day did not exhibit the same impulsive behavior. The research also revealed significant sex differences: female flies showed much greater caffeine-induced impulsivity than males, despite similar caffeine levels. “Flies don’t have human hormones like estrogen, so other genetic or physiological factors likely drive the greater sensitivity in females,” explained Han. These findings raise concerns for people who consume caffeine at night, particularly shift workers, healthcare professionals, and military personnel, especially women. This study was conducted in Han’s lab at UTEP’s Department of Biological Sciences, which specializes in the neurobiology of behavior, addiction, and related diseases.