Alcohol and Cannabis – The Science Behind How They Interact

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Alcohol and cannabis are two of the world’s most popular recreational drugs. It is not surprising then that they are often consumed together.

Some people report that they feel pretty good after combining cannabis with a few drinks. There are also many cases of extreme dizziness, nausea, or blacking out. Many people know their limits for each drug individually, but things are always harder to get right in combination.

There is a saying I heard:

Weed before beer; you’re in the clear.
Beer before grass; you’re on your ass.

Could there be a scientific reason for this?

This combination of drugs has also been a popular topic of scientific study. There are dozens of experiments going back to the 1970’s. I delve into the research to see what science says about this combination.

Effect of Alcohol on THC Levels

Several studies have explored whether alcohol can change the pharmacokinetics (i.e. blood levels) of THC after either smoking or vaporizing cannabis. The results have been mixed, although 2 out of 4 studies showed that alcohol increases blood THC levels. These two studies showed over a 50% increase in blood THC levels after consuming alcohol.

One study showed a dose-dependent effect. In other words, the more alcohol that was consumed, the bigger the increase in THC levels. Since these studies used only low to moderate (about 3 shots worth) alcohol consumption, we don’t know what would happen if even more alcohol was consumed.

drug-interaction-alcohol-cannabis-thc-levelsThese scientists have offered several explanations for why THC levels are higher after alcohol consumption:

  • Vasodilation (the blood vessels are more relaxed) in lung capillaries from alcohol increases THC absorption
  • After drinking, people tend to take deeper hits

Either way, the effect seems to be related to the absorption of THC and thus, if you start drinking after you have already smoked, there should no effect of the alcohol on THC levels.

Effect of Cannabis on Alcohol Levels

Although alcohol appears to increase levels of THC, cannabis has quite the opposite effect on blood alcohol levels. Studies have shown that after consuming cannabis, blood alcohol levels do not rise as fast.

One study showed that when smoking a joint 30 minutes after taking a drink, the peak blood alcohol levels were 30% lower. Not only that, but it took twice as long to even reach the maximum blood alcohol level.

drug-interaction-alcohol-cannabis-alcohol-levelsThis effect could be related to how cannabis slows gastric emptying time (the time for the contents of your stomach to make it to your intestines, where things are better absorbed).

Cross-Tolerance Between Alcohol and Cannabis

The above sections describe what happens with a single dose of alcohol and cannabis. But what happens when you are a regular cannabis user? Science shows that even in the absence of recently consuming cannabis, being a regular cannabis user can affect how you react to alcohol.

Anyone who has been drunk knows that the symptoms include dizziness and lack of motor coordination. But people who drink regularly enough will notice that it takes more and more alcohol to produce these same effects. This is called tolerance.

In mice, motor coordination is tested with a device called a rotarod. Basically, they put a mouse on a rod that starts spinning and they see how long the mouse can stay on it before they fall off.

rota_2

Like a drunk lumberjack, alcohol decreases the performance of mice on the rotarod test. But given regular alcohol, they will develop tolerance and stay on the rod longer.

Here’s where things get interesting: If  mice are given daily cannabis, they retain their motor function better after they are given alcohol! When one drug produces tolerance to the effect of another drug, it is called cross-tolerance.

But does this cross-tolerance between alcohol and cannabis happen in humans? Yes!

One study has shown that after being given an amount of alcohol which makes infrequent cannabis users dizzy, there was no increase in dizziness for regular cannabis users. Similarly, on a computerized tracking task that measures driving performance, alcohol made infrequent cannabis users score worse, but not regular cannabis users.

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[Flickr/huggs2]

Don’t go thinking that because you are a regular cannabis user you can now drive drunk. There was a similar worsening in reaction time for both infrequent and regular cannabis users.

In fact, you may wish to be more cautious of driving after imbibing if you are a regular cannabis user. You may not feel uncoordinated, leading you to think that you are ok to drive, but other key driving skills are still impaired.

Still, how cool is it that being a cannabis user reduces some of the unpleasant effects of alcohol!

[Featured Image Credit: Flickr/ Elvert Barnes]

Last modified: June 2, 2017

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