They say you should never go food shopping on an empty stomach because you'll end up bringing home half the snack aisle. But according to a new study, it's not just what we eat that can affect our spending habits, it's also what we drink. And if you're looking to stick to a budget, you might want to skip the caffeine

Consuming caffeine can be bad for your budget. 

The study, recently published in the Journal of Marketing, had a simple but ingenious design. The researchers set up a stand at the entrance of three home goods and department stores in Europe offering shoppers free espresso. Some were given a full-strength brew while others got decaf. In exchange, the shoppers had to take a short survey about how they felt while shopping and also share their receipts with the researchers. 

It will come as no surprise to coffee drinkers that those given a regular espresso reported feeling more alert and excited while shopping. That's the point of caffeine, after all. But you probably didn't realize caffeine has effects on more than your mood. It also apparently makes you more likely to reach for your wallet. 

Those who consumed caffeine bought more items and spent more overall than those who were given decaf. They also bought different things. Those who had a regular espresso bought more decorative and non-essential items like scented candles and perfume. Purchases of more practical items, like toilet brushes, were relatively unchanged. Which suggests when you're feeling a little buzz from your morning brew you're more likely to give in and pick up impulse purchases you didn't plan on buying. 

A two-pronged takeaway 

The lesson here for those looking to trim their spending is pretty clear: Coffee isn't bad for your body and may even benefit your health, but it can also make it easier to bust your budget. So maybe skip that second Americano before heading out to the mall or booting up Amazon. More caffeine will not help you make the soundest financial decisions

Those operating retail establishments can take exactly the opposite lesson from this study. Handing out a complimentary cup of coffee won't just make your customers happy, it might also make them spend more in your store. Which means that whatever you invest in beans and an espresso machine might be more than made up for in extra purchases. It's worth a try at least.