Challenging what researchers have long believed about hangovers, a landmark study conducted by the Alcohol Learning Establishment (ALE) has identified a previously overlooked factor: alcohol.

Hangovers are generally defined as some combination of headaches, grogginess, nausea, fatigue, dizziness, or other unpleasant symptoms. “For years, we believed hangovers to have primary causes like dehydration, waking up too early, or garnishes on a beverage,” says Dr. James Woolworth, lead researcher at ALE. “In this double-blind study, we ruled several of these out in what we believe are fairly conclusive ways, and we found there may be at least some correlation between alcohol and hangovers.”

In the study, they had two groups drink at a small bar in what researchers described as a ‘controlled environment.’ One group had drinks until they reached a .08 Blood Alcohol Content – making them quite drunk. The other group had only nonalcoholic drinks. The controlled bar “played hair metal hits from the 1980s, dim lighting, and an uneven pool table,” according to the paper.

First, he said, they ensured that all the participants in the night-long study were adequately hydrated, measured by urine analysis and blood testing. They then ensured all participants were in bed by midnight, allowing them plenty of time to sleep before they were awoken at 9AM. 

The study showed that out of 90 participants given alcohol, 89 of them woke up with some level of hangover. Out of the 90 participants that didn’t drink alcohol, not a single one woke up with a hangover. 

“Most importantly, we found that there was no difference between participants having garnishes on their alcoholic drinks and those that didn’t,” Dr. Woolworth said. He had led an ALE study into garnishes in 2013, with fairly conclusive evidence pointing to garnishes on cocktails (including things like salt on a margarita rim) as the culprit. “This really shakes up the foundations of our understanding of hangovers,” he said.

We contacted Ingrid Beverly, a PR spokeswoman from Anheuser-Busch, the maker of Budweiser, for comment on how the company views these findings. 

“There’s nuance to these findings, and correlation does not equal causation,” her statement began. “I’m sure I don’t need to remind these researchers that, but it’s important for everyone to note that there were other factors involved, including loud music and dim lights – both things that are known to cause headaches in some people.”

“What’s more, they very well could have been drinking Coors, which our independent researchers found to cause headaches in each participant in a similar, single-blind study,” she concluded. It is worth noting that Coors, another popular beer, is made by Anheuser-Busch’s rival, Molson-Coors.

When asked what this study means for the future of alcohol research, Dr. Woolworth sounded excited. “We are already planning a follow-up study, where we intend to give participants hangovers, and then see if drinking again helps to reduce their symptoms. We’re optimistic it may lead to further insights.”