Shoppers, beware that little coffee shop that just popped up inside your favorite retail store. What might seem like an innocent enough frappuccino could lead you down a dark path of impulse purchasing, according to new research. 

Drinking just one cup of caffeinated coffee prior to a shopping spree could result in you spending around 50 percent more money than if you’d stuck to the decaf or opted instead for water. You may also find yourself buying up to 30 percent more items, the study published in the Journal of Marketing found.

And it’s not just the amount of money spent or number of purchases that caffeine can affect – it may impact the types of items we purchase too, potentially pushing us toward frivolities.

“Caffeine, as a powerful stimulant, releases dopamine in the brain, which excites the mind and the body. This leads to a higher energetic state, which in turn enhances impulsivity and decreases self-control,” lead author Dipayan Biswas said in a statement. 

“As a result, caffeine intake leads to shopping impulsivity in terms of higher number of items purchased and greater spending.”

In a series of experiments, Biswas and colleagues offered complimentary coffee to shoppers at the entrance of a homeware retail store in France and a department store in Spain. More than 300 people were offered a free drink – caffeinated espresso, decaffeinated espresso, or water – at the start of their trip and then asked to share their receipts as they left the store.

Buoyed by the buzz of caffeine, shoppers who drank the caffeinated coffee spent significantly more money and bought significantly more items than those who didn’t. In one study, for example, shoppers drinking caffeinated espresso spent an average of €27.48 ($28.91) and bought an average of 2.16 items, compared to an average spend of €14.82 ($15.59) on 1.45 items for those on the decaf.

Shoppers drinking caffeine were also more likely to splash out on non-essential items, such as candles and fragrances than the control groups. However, there was hardly any difference in spending between the two groups when it came to utilitarian items, such as kitchen utensils. 

Similar results were found in another study, this time involving online shopping and 200 volunteers. Asked to pick from a list of 66 items, individuals were more likely to click add to cart on impulse items, like a massager, after a coffee. Meanwhile, the uncaffeinated group tended to make more practical choices, like a notebook.

And, the study found, some of us are more susceptible to the spendthrift effects of coffee than others. Moderate coffee drinkers – people drinking up to two cups a day – are most likely to impulse purchase after a pre-shopping pot. For heavy coffee drinkers, though, its effect seems to be diminished.

It hardly seems surprising, then, that so many malls and department stores are home to coffee shops, given that the coffee they serve may provoke us into parting with our pennies. 

As a consumer, perhaps it may be best to save the caffeine boost until after you’re done splashing the cash, Biswas warns.

“While moderate amounts of caffeine intake can have positive health benefits, there can be unintended consequences of being caffeinated while shopping,” Biswas concluded. 

“That is, consumers trying to control impulsive spending should avoid consuming caffeinated beverages before shopping.”