I rarely mix weed and alcohol—otherwise, I become more silent than a hermit crab floating in space.
But pursuing the high that results from combining the two drugs—known as a "crossfade"—isn't uncommon. Researchers, however, are still delving into the science behind this blissed-out state of mind—and why so many people seek it out.
Let's start with what you probably already know: Alcohol is a depressant, but in low doses it causes emotional release and lowers inhibitions. Marijuana is also known for its relaxing qualities, but can produce very different results depending on how much and what strain of it you smoke. So what happens when you mix them together?
The first thing to know: "Not everyone responds to alcohol and marijuana the same [way]," says Scott Lukas, a professor of psychiatry and pharmacology at Harvard Medical School. Lukas would know: He's now done two studies in which he got people high and observed their reactions.
One study looked at how smoking weed affects the absorption of alcohol, and the other looked at how drinking alcohol affects the absorption of THC. Smoking cannabis, he found, activates your body's cannabinoid 2 receptors (CB2), which can affect how quickly your body absorbs alcohol.
"Marijuana does a unique thing to your small intestine that alters the motility [the way things move through your intestines] of your GI tract in such a way that it causes your blood alcohol levels to actually be lower than…if you had just consumed alcohol by itself," Lukas says.
But in the second study, Lukas found that alcohol actually has the inverse effect on THC: If you drink first and then smoke, it causes the levels of THC in your plasma to skyrocket, intensifying your high. That's because alcohol opens up blood vessels in your digestive system, which helps THC get absorbed—a finding confirmed in a more recent study done in 2015.
As most recreational marijuana users can attest, however, there are limits to this feel-good effect: Drink too much before you smoke, and you run the risk of "greening out"—a nauseous sensation that kicks in when you feel sick and overwhelmed after getting too high. (Trust me, it's no fun.)
"Individuals may go pale and sweaty, feel dizzy with 'the spins,' nauseous, and may even start vomiting. This is often followed by the need or strong desire to lie down," wrote Constance Scharff, an addiction specialist in California, in a column for Psychology Today.
More modern methods of ingesting THC—like dabbing, vaping, or eating cannabis—could further exacerbate this risk, but Lukas hasn't had a chance to study them yet. He notes, however, that the THC levels now commonly found in cannabis and cannabis products greatly exceed the amounts he used in his studies.
Using common sense will go a long way: Lukas says there aren't many side effects that come from mixing the two drugs that won't also be true if you do them independently. Just be careful not to overdo it, and always err on the side of caution.
"If you're sitting alone in your bedroom," he says, "and you've got pillows all around you, and you're well hydrated, and the bed's not too far off the ground, the risk is low."
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