New research shows decaf coffee can mimic caffeine’s effects in habitual drinkers

A new study published in Heliyon suggests that the energizing effects of coffee might have less to do with caffeine and more to do with the ritual of drinking it. In a double-blind, placebo-controlled experiment involving habitual coffee drinkers, researchers found that ingesting decaffeinated coffee produced many of the same physiological and cognitive responses as caffeinated coffee. These findings suggest that regular coffee consumers may react to the experience of drinking coffee in ways that are independent of its caffeine content.

Coffee is a cornerstone of daily life for billions of people around the world. Its perceived benefits include enhanced alertness, improved focus, and a sense of readiness to take on the day. While these effects are typically attributed to caffeine, some researchers have argued that other factors—such as the smell, taste, or even the expectation of coffee—might also play a role. In particular, habitual coffee drinkers may develop conditioned responses, where the mere act of consuming coffee triggers physiological changes regardless of whether caffeine is actually present.

“Caffeine is something we use everyday, yet is poorly understood, and thus makes an inviting study subject. We wanted to understand what actually triggers the physical and mental effects people associate with coffee, especially in regular drinkers,” said study author Mateja Lesar, a research assistant at the Faculty of Information Studies in Novo Mesto.

“Is it the caffeine, or could it be the ritual itself? The act of drinking coffee has a clear ‘ritualistic’ dimension associated with it, but its impact is hard to separate from the impact of caffeine. To explore this, we sought to separate the effects of caffeine from the experience of drinking coffee by using decaf that looks, smells, and tastes just like regular coffee. This allowed us to investigate how much of the response is driven by expectation and habit compared to the caffeine.”

For their study, the researchers designed a controlled experiment focused on separating the effects of caffeine from the psychological and physiological effects of the coffee-drinking ritual. The study recruited 20 healthy university students (10 male and 10 female) who were habitual coffee drinkers, consuming one to three cups per day. All participants abstained from caffeine for at least eight hours before the experiment.

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The participants were randomly assigned to receive either caffeinated or decaffeinated coffee. Importantly, both beverages were identical in appearance and taste, and both were made using decaffeinated coffee beans—with caffeine powder added back into the drink for the caffeine group. This approach ensured that participants in both groups believed they were drinking regular coffee. Throughout the experiment, participants underwent several assessments both before and after coffee consumption: their heart rate and blood pressure were measured, they completed a mental arithmetic test and an auditory attention task, and their brain activity was recorded using electroencephalography (EEG).

The researchers hypothesized that if caffeine was responsible for the alerting effects of coffee, then participants who consumed caffeinated coffee would exhibit more pronounced changes in cardiovascular and cognitive performance, as well as distinct patterns of brain activity, compared to those who received the placebo.

Surprisingly, the results did not fully support this expectation. Across the board, both groups showed similar physiological changes following coffee ingestion. Heart rate decreased and blood pressure increased after consuming either drink, with no significant differences between the caffeine and placebo groups.

“Both decaf and a high dose of caffeine produced similar cardiovascular effects,” Lesar said. “If anything, here is where we would expect a discrepancy between the two beverages, since these are harder to attribute to ritual.”

Cognitive performance was also largely unaffected by the presence of caffeine. In a mental arithmetic task, participants’ accuracy and number of responses did not change significantly after drinking either type of coffee. In contrast, reaction times during an auditory attention task improved slightly in both groups. However, this improvement was statistically significant only for the caffeine group. While this suggests that caffeine may enhance processing speed, the fact that the placebo group also improved—despite ingesting no caffeine—points to a possible placebo effect, fueled by the participants’ expectations.

The EEG data revealed more subtle distinctions. During the attention task, brain wave patterns associated with cognitive processing (specifically, the P3 component) increased in both groups after coffee consumption. However, only the caffeine group showed a statistically significant increase. Resting-state EEG data also showed a significant interaction between group and ingestion condition, with changes in alpha and beta wave activity found across several brain regions. One specific finding—the decrease in alpha power at the FC2 electrode in the caffeine group—suggests increased mental readiness, as lower alpha activity is often linked to heightened attention and reduced inhibition.

Taken together, these results paint a nuanced picture. While caffeine had measurable effects on brain activity and reaction time, many of the physiological and psychological responses traditionally attributed to caffeine were also present in the placebo group. This suggests that habitual coffee drinkers may be responding not just to the drug itself but also to the context and ritual of coffee consumption.

“Our results indicate that habitual coffee drinkers may experience conditioned responses, which are independent of the presence of caffeine,” Lesar told PsyPost. “In other words, once we are used to caffeine and expect to ingest it via a nice cup of coffee, even a cup of decaf will have (nearly) the same effect on us.”

The findings are consistent with a growing body of research suggesting that the experience of drinking coffee—its smell, taste, and associated expectations—can influence alertness and cognitive performance. For instance, previous studies have shown that simply smelling coffee or being told one has consumed caffeine can boost reaction times. A recent functional MRI study even found that coffee, but not caffeine alone, activates brain regions involved in memory and goal-directed behavior.

Like all research, the study has limitations. The sample size was small—only 20 participants—limiting the statistical power to detect subtle effects. All participants were habitual coffee drinkers, so the results may not generalize to people who rarely consume coffee. Additionally, while decaffeinated coffee was used as a placebo, it still contains trace amounts of caffeine and other biologically active compounds, which may contribute to the observed effects.

Future research could build on these findings by including larger and more diverse samples, comparing habitual and non-habitual drinkers, and testing other forms of placebo. The researchers are also interested in using more advanced techniques to explore how neural responses to coffee are shaped by psychological expectations.

“We would like to further investigate how perceptions influence the effects of caffeine,” Lesar explained. “We suggest further research into the complex psychological and physiological effects of caffeine and coffee consumption, with a focus on habituation, placebo effects, and the impact of study design choices. Larger and more diverse samples, comparisons between habitual and non-habitual drinkers, and consideration of coffee’s other active compounds are all interesting avenues for future studies. We would also suggest analyzing the empirical data with advanced tools of data analysis, including machine learning and network analysis. In fact, we already started with the machine learning classification.

“Carrying out this study made us learn new things about coffee and peoples’ perception of it,” Lesar added. “We also had a chance to drink a few cups ourselves during long afternoons of EEG measurements.”

The study, “The complexity of caffeine’s effects on regular coffee consumers,” was authored by Mateja Lesar, Jakob Sajovic, Dušanka Novaković, Maša Primožič, Eva Vetrih, Martin Sajovic, Anja Žnidaršič, Peter Rogelj, Andreas Daffertshofer, Zoran Levnajić, and Gorazd Drevenšek.