You know that friend, the one who only smokes when she drinks? Or that guy, the one who says he’d quit cigarettes if they just didn’t pair so nicely with a cold beer?

New science is helping explain what exactly is happening in our brains that makes us crave nicotine and alcohol together.

The University of Missouri School of Medicine gave the drugs to rats to study how it affected their sleep. Normally, drinking alcohol will make you sleepy, which will eventually cause you to stop drinking. But if you take nicotine at the same time, it acts as a stimulant, counteracting the sleepiness and allowing you to keep drinking.

“If an individual smokes, then he or she is much more likely to consume more alcohol, and vice-versa. They feed off one another,” said lead author Mahesh Thakkar in a statement.

This turns out to be a big problem. Previous research has suggested that up to 90 percent of people with a drinking problem also smoke, and the vast majority smoke at least at a pack a day. According to the World Health Organization, alcohol and tobacco cause close to 15 percent of deaths worldwide.

Despite the fact that a tobacco addiction can spur alcoholism, few drug and alcohol treatment programs treat nicotine dependence.

The researchers hope that understanding the neural link between booze and cigarettes will one day lead to better treatments. Will we one day ingest nicotine-eating bacteria to curb cravings? Or perhaps it’s hallucinogenic mushrooms that will one day cure our addictions.