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Every morning, people turn to coffee — the fuel of choice for millions — to help them make it through the bustling chaos of another busy day. Coffee is a stimulant that ramps up activity in the brain and central nervous system, but a new study surprisingly found that among the myriad ways that coffee affects the metabolism, it also targets neurotransmitters linked to cannabis.

Metabolites are molecules produced by metabolic reactions catalyzed by various enzymes that naturally occur within cells. Scientists at Northwestern University found that coffee consumption altered many more metabolites in the blood than previously thought. One of the most striking findings was that cannabinoids decreased after drinking four to eight cups of coffee in a day. This is the opposite effect of what happens after a person uses cannabis. Cannabinoids are secondary metabolites, meaning they’re substances that the plant produces which have no primary purpose in its development, whether it’s reproduction, photosynthesis or growth.

Cannabinoids act on the central nervous system by imitating endocannabinoids, molecules which occur naturally in the human body. They’re the chemicals that are responsible for the medical and recreational properties of cannabis. Not all of them, however, are nearly as potent as THC. In fact, most of them aren’t psychoactive at all. For instance, Cannabidiol  (CBD) — another cannabinoid and possibly the 2nd most famous one after THC — is not only nonpsychoactive, it actually blocks the high from THC.

Another class of metabolites whose activity has now been linked to coffee consumption are related to the androsteroid system. These metabolites increase upon drinking four to eight cups of coffee in a day, facilitating the excretion of steroids. The steroid pathway is involved in certain diseases — chief among them cancer — suggesting coffee can have a significant effect on these diseases.

The findings were made after the team led by Marilyn Cornelis, Assistant Professor of Preventive Medicine at Northwestern University Feinberg School of Medicine, applied modern analytical technology that enabled them to measure hundreds of metabolites. Blood was sampled regularly from 47 participants from Finland who were asked to abstain from coffee for one month, then consumed four cups a day for the second month and eight cups a day in the third month.

More than 800 metabolites were tracked in the blood collected at each stage of the three-month trial. “Over 100 metabolites changed in response to coffee and while many were worthy of discussion we had to limit our focus/discussion to a few key subsets,” Cornelis told ZME Science.

Because some endocannabinoids are known to decrease when the body is under stress, Cornelis and colleagues believe the increased coffee intake over the span of two months may have stressed the body. The decrease in endocannabinoids may be our bodies’ way of adapting to the stressor. “These metabolites decreased particularly with 8 cups/d over the course of a month,” Cornelis wrote in an e-mail. And because the endocannabinoid pathway is involved in a wide array of bodily functions, including appetite, coffee should also impact eating behavior.

While cannabis is famous for giving you “the munchies”, coffee suppresses appetite. Previously, studies linked coffee intake to successful weight management and a reduction in the risk of developing type 2 diabetes, but the association was pinned on caffeine’s ability to “boost fat metabolism or the glucose-regulating effects of polyphenols (plant-derived chemicals),” Cornelis said. The new findings suggest coffee’s impact on endocannabinoids offer an alternative explanation worth pursuing further.

So, what do these findings imply for those who wake and bake with a cup of joe?

“Whether elevated blood levels of plant-derived cannabinoids (resulting from cannabis use) offset the lower levels of endocannabinoids produced by the body naturally (in response to coffee) or vice versa is unknown but one can imagine this might impact the effects of either substance/beverage. Coffee is a very common beverage and it’s highly possible that cannabis users are also coffee consumers,” Cornelis told ZME Science.

Next, the researchers plan on delving even deeper into their data and analyze new pathways that may be potentially affected by coffee.

“I’m currently working with more biomarker data that we’ve measured in the blood of these trial participants. These include lipids and proteins. We hope to identify additional pathways impacted by coffee or possibly more insight into the pathways we’ve uncovered in this latest study. Much of my earlier research has focused on genetics of coffee consumption and caffeine metabolism. I hope to incorporate some of that work into the new findings but this will require much more data and participants. Much to look forward to!”

“Seems every month we hear about a study linking coffee to some disease or condition. In most, if not all, cases that’s all we know. Whether its causal or just how coffee impacts the disease is often unknown. This latest research provides insight to the latter and therefore pushes the coffee research forward,” Cornelis concluded.

The findings appeared in the Journal of Internal Medicine.