How Much Alcohol Causes a Hangover?

Science says it’s not about counting drinks — it’s about how you feel.

Over the past two decades, researchers have learned a surprising amount about hangovers. We now know that some types of alcohol cause worse hangovers than others, dehydration isn’t the main culprit, and hangovers tend to peak when your blood alcohol concentration (BAC) returns to zero.

In the early 2010s, scientists suggested that reaching a BAC of around 0.11% almost guaranteed a hangover the next day — leading many to believe there was a universal “hangover threshold.”

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According to a recent study led by Toast!’s scientific advisor, Dr. Joris Verster, early hangover research relied heavily on university students — a group that drinks more frequently and develops higher tolerance than the general population.

When researchers studied non-students, they found that much lower BACs could still cause hangovers. In other words, that 0.11% “rule” isn’t very reliable.

The Real Predictor: How Drunk You Feel

Dr. Verster and his colleagues found that subjective intoxication — how drunk you feel — is a better predictor of hangovers than BAC.

Everyone’s alcohol tolerance is different. Age, weight, genetics, and drinking habits all play a role. You can usually drink within your tolerance without consequences, but once you exceed it, hangovers become far more likely.