PORTLAND, Ore. (KOIN) – A new study evaluating the combined effects of alcohol and caffeine found that both substances, when used together, have an “unexpected” effect on sleep.

Researchers at the University of Washington and University of California-Berkley hypothesized that combining caffeine and alcohol, “the two most popular psychoactive drugs in the world,” would decrease sleep quantity and quality.

For six weeks, 17 study participants — who worked in financial trading — logged their drink consumption and their quantity and quality of sleep.

The study, which was published Wednesday in the journal PLOS ONE, found that on average caffeine reduced sleep quantity by 10 minutes per cup consumed the previous day.

Those who drank alcohol the day before reported a 4% decline in their sleep quality on average, according to the study.

However, researchers discovered when the participants drank both caffeine and alcohol, the negative impacts each have on sleep were seemingly offset.

“Compared to the nights when you might have one or the other, we thought we were going to see additional decline in subjective sleep quality or sleep duration,” said lead researcher Frank Song, a fourth-year clinical psychology doctoral candidate in the University of Washington’s Department of Psychiatry and Behavioral Sciences.

“But actually, that interaction effect was the opposite of what we expected and ended up having an effect of offsetting each other’s negative impact on quality or quantity. And this was very intriguing to us,” Song continued.

However, the researchers believe this is only a short-term effect.

“What we find is that while there may be greater alertness in the short term, it creates a sleep-state misperception contributing to continued use, despite negative effects on sleep,” Song said.

He said even though the participants were getting less sleep, they weren’t able to notice a decrease in their sleep quality.

“This concerns us and leads us to believe in the long run, it actually perpetuates this cycle of alcohol and caffeine use while the individuals are unaware of the negative effects on sleep,” Song said.

The study found participants eventually turned to a cycle of self-medication to offset the effects of either alcohol or caffeine.

“Over time, it turns into a cycle of self-medication, as some may call it, in the real world where people will experience bad sleep as a result of alcohol-induced REM sleep suppression,” Song said. “And they will try to mitigate that with caffeine use in the daytime.”

He said the main takeaway is that people can modify their alcohol and caffeine consumption for better sleep, but researchers aren’t suggesting people drink an excessive amount of coffee or liquor. The study states that more research is needed to further understand these effects.