Scientists found that people who sip on a complimentary cup of coffee while shopping end up spending 50% more money and buying 30% more items than their non-caffeinated counterparts. Researchers from the University of South Florida (USF) set up an espresso machine at the entrances of a retail chain and home goods store in France, as well as a department store in Spain, according to Study Finds.

When customers entered the stores, they received a free coffee cup. Half of those shoppers ordered coffee with 100 mg. of caffeine, while the other half ordered decaffeinated coffee or water. Later, they shared their receipts with the USF researchers. It turns out that people who drank caffeinated coffee bought more items and spent more money.

“Caffeine, as a powerful stimulant, releases dopamine in the brain, which excites the mind and body,” said lead author Dipayan Biswas, the Frank Harvey Endowed Professor of Marketing at USF. “This leads to a higher energetic state, which in turn enhances impulsivity and decreases self-control. As a result, caffeine intake leads to shopping impulsivity in terms of a higher number of items purchased and greater spending.”

The researchers also discovered that the caffeinated shoppers purchased more non-essential items such as scented candles and fragrances than the other shoppers. There was little difference in the purchases of practical items such as kitchen utensils and storage baskets between both groups.

They then set up another experiment, this time in a lab to analyze online shoppers. A group of 200 business school students were split into those who consumed caffeinated coffee and those who drank decaf. The students were asked to select items to purchase from a preselected list of 66 options. Once again, the people with caffeine in their system chose more impulsive purchases like massagers, while the decaf drinkers selected more practical items, such as a notebook.

“While moderate amounts of coffee intake can have positive health benefits, there can be unintended consequences of being caffeinated while shopping, said Biswas in a university news release. “That is, consumers trying to control impulsive spending should avoid consuming caffeinated beverages while shopping.”

Their study was published in the Journal of Marketing.