When alcohol and marijuana are used together, each substance amplifies the other’s effects in ways that go beyond what either produces alone. The combination raises THC levels in your blood, impairs coordination and judgment more severely, and increases the risk of a sudden, intensely unpleasant reaction sometimes called “greening out.” This isn’t a niche behavior: millions of adults in the U.S. report using both substances on the same occasion, and many underestimate how differently the two interact compared to using them separately.
How Alcohol Changes the Way Your Body Absorbs THC
The most well-documented interaction is straightforward: drinking alcohol before smoking or consuming marijuana results in higher THC levels in your bloodstream than marijuana alone would produce. A study published in Clinical Pharmacology & Therapeutics found that volunteers who drank alcohol before smoking marijuana detected the effects more quickly, reported more episodes of euphoria, and had measurably higher plasma THC levels than those who drank a placebo before smoking the same amount of cannabis.
The likely reason involves how alcohol affects blood vessels and absorption in the lungs and gut. Alcohol increases blood flow and may open up the lining of the digestive tract and airways, allowing THC to pass into the bloodstream faster and in greater quantities. The practical result is that your usual amount of marijuana can hit significantly harder after a few drinks, even if you feel only mildly buzzed from the alcohol itself.
How Cannabis Slows Alcohol Processing
The interaction runs in both directions. THC slows gastric emptying, the rate at which your stomach pushes its contents into the small intestine. Research on the synthetic form of THC (dronabinol) has confirmed this effect, with one finding showing it was especially pronounced in women. When your stomach empties more slowly, alcohol sits there longer before being absorbed, which can flatten and delay its peak effects in unpredictable ways.
This might sound like it would make alcohol feel weaker, but the timing becomes erratic. You may feel relatively sober for longer, drink more as a result, and then experience a delayed surge of intoxication as the alcohol finally moves through. The mismatch between how intoxicated you feel and how much alcohol is actually in your system creates a real risk of overconsumption.
Why the Combination Hits Harder Than Either Alone
Both substances independently slow reaction time, cloud judgment, and impair coordination. Together, these effects don’t simply add up. Research on driving performance has found that combining even low doses of alcohol with low doses of cannabis causes substantially more impairment than either substance used alone. The effects are described as additive and potentially synergistic, meaning the total impairment can exceed what you’d predict by simply stacking the two.
One reason is that marijuana and alcohol impair different aspects of performance. Alcohol primarily affects inhibition and risk assessment: you make worse decisions about speed, following distance, and whether to attempt a maneuver. Cannabis primarily disrupts attention and the ability to handle unexpected events. A driver who has used only cannabis tends to compensate somewhat by driving more cautiously, slowing down and increasing following distance. Adding alcohol eliminates that compensatory strategy entirely. The result is someone who can’t respond well to surprises and also isn’t trying to.
This applies well beyond driving. Any activity requiring coordination, timing, or situational awareness becomes substantially riskier with the combination.
What “Greening Out” Feels Like
The acute adverse reaction most associated with combining these substances is commonly called greening out. Symptoms include turning pale, heavy sweating, dizziness, intense nausea, and the sensation of the room spinning. In more severe cases, a person may experience a panic attack layered on top of the physical symptoms, which can feel overwhelming and sometimes mimics the sensation of a medical emergency.
Greening out is far more common when alcohol is involved than with cannabis alone, precisely because alcohol pushes THC levels higher than expected. You smoke what feels like a normal amount, but your body is processing it as a much larger dose.
There’s an additional danger that is less widely known. Cannabis has antiemetic properties, meaning it suppresses the vomiting reflex. Vomiting is one of the body’s primary defenses against alcohol poisoning: when blood alcohol climbs dangerously high, the body tries to expel what’s still in the stomach. If cannabis is suppressing that reflex, more alcohol continues to be absorbed, and the risk of alcohol poisoning increases. This is one of the more serious medical concerns with co-use, and it’s not something most people are aware of when they combine the two.
The Liver Processes Both Through Overlapping Pathways
Your liver uses the same families of enzymes to break down both alcohol and cannabinoids. The enzymes most involved in THC metabolism are the same ones that process a wide range of substances, and alcohol’s byproducts also pass through overlapping pathways. When both substances are present simultaneously, they essentially compete for the same processing machinery.
This enzymatic competition is one reason each substance lingers longer and reaches higher concentrations when the other is also present. It also means that people who regularly use both substances may be placing a higher metabolic burden on the liver than they would from either substance alone, though the long-term organ-level consequences of this specific combination remain an active area of study.
Does the Order You Use Them Matter?
The common saying “beer before bong, you’re in the wrong; bong before beer, you’re in the clear” reflects a widespread belief that the sequence matters. The science is surprisingly thin on this point. Only one study has directly examined order effects at the daily level, and it found that using cannabis first on a co-use day was associated with drinking less alcohol overall but using more cannabis. The effects of order on how intoxicated people feel, or how severe the interaction becomes, have not been rigorously tested in controlled settings.
What is clear from the pharmacology is that drinking first and then using cannabis will reliably spike your THC levels higher than cannabis alone would. Whether reversing the order meaningfully reduces risk is something researchers have proposed studying but haven’t yet answered with strong evidence. The safest assumption is that combining them in any order produces a more intense and less predictable experience than either one solo.
Practical Risks to Keep in Mind
The CDC’s guidance on this combination is blunt: using alcohol with cannabis can produce effects that are stronger and more dangerous than using either one alone. Several practical risks stand out:
- Misjudging your level of intoxication. Because the two substances alter absorption timing for each other, you may feel less affected than you actually are, leading to more consumption of one or both.
- Impaired vomiting reflex. Cannabis can suppress your body’s ability to vomit, removing a key safety mechanism against alcohol poisoning.
- Amplified THC effects. Even your usual amount of cannabis can produce an unexpectedly intense high when alcohol is in your system.
- Severely impaired motor skills. The combination degrades coordination and reaction time more than either substance alone, with effects that may be multiplicative rather than simply additive.
If you do use both, the most actionable thing you can do is use significantly less of each than you normally would on its own. The combination changes the math on what counts as “a little,” and the margin between a manageable experience and a miserable one narrows considerably.