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Was your memory different on 4/20?

Let's weed out what we do and don't know about weed and memory.

Hey, it was 4/20 recently, so I HAVE to ask, do you smoke weed? Do you ingest THC or CBD separately through other means? Well, each of these likely have different effects on your memory…and you should know that. You should also know, it may or may not actually work out the way I say, depending on you, the person who consumes weed.

Let me start with the findings (citation at the end of the article).

All the findings are from a small review of studies done to understand possible ways that cannabis may affect memory. This was broken down into 3 main sections: smoking cannabis, THC, and CBD.

Smoking Cannabis:

There is a lot we still don’t know, but as weed becomes more and more legal, we’ll find out more about the actual effects, both good and bad (yes, of course there is likely both). Nothing I say here is an explicit endorsement of or criticism of weed. It’s literally just letting you know that these are things you can expect, according to science.

What we generally know, however, is that even after smoking weed even for a short period (e.g., a few days), we are worse at holding information in our heads. We also have a harder time manipulating that information that we are thinking about and remembering it later.

These effects can last EVEN AFTER the weed has been fully processed by your body. That is, researchers have tested memory function even 24 hours after smoking, and there were still memory deficits.

The memory issues only get worse when people are heavily using cannabis.

So, what might be happening. Well, we can take a look into the brain of people who smoke weed and see what is different compared to those that don’t. There are 2 brain regions that seem to relate to weed use: the anterior cingulate cortex and the thalamus.

What are those? Good question.

I’ll say a couple things. No brain region is really just for one function and what happens in a person’s brain may differ depending on their development. Just because in general there is less activation and functioning of a part of the brain doesn’t mean we know exactly what is happening. I’m going to try to explain this idea, but I will put it in parentheses and feel free to skip this next part if it is confusing.

(The main thing I want to say is that, just because, on average, there is less brain functioning, that alone doesn’t really mean much of anything. This is because, for each individual, this may not be the case. Maybe out of 100 people, 70 have less brain functioning and 30 have more brain functioning. What do we do with that information? Maybe for 35 there is more brain functioning in certain parts, and for the other 35 there is less brain functioning in other parts. Maybe that pattern is completely reversed. That is part of it that we don’t know with enough specificity what is happening. The other part that is highly related to this idea is that even if we did know with specificity the areas that are impacted, we definitely still don’t know the functions of each part of the brain. This is mainly because there is no single function for any given part of the brain. And what that set of functions is will definitely differ in strength, capacity, and how it connects to other parts of the brain. There are generally around 100 trillion connections in the brain. That is 100 TIMES 1,000,000,000,000. Do we really think the brain is going to make all the same connection when we have such wide varieties in experiences, hormones, health, stress, etc.? Anyway, I’ll go back to the main point of this article again).

People that regularly smoke weed will still have less activation in the anterior cingulate cortex and the thalamus EVEN AFTER they haven’t been smoking for some time. So, what does that mean? Some functions of the anterior cingulate include decision making, attention, and error detection. The thalamus generally does things involving consciousness and alertness. If your attention is low and you aren’t alert, do you think you’ll be able to remember anything? If you are literally on the borderline between being conscious or not, you are probably more concerned about other things! There are even functions dealing with heart rate within these areas of the brain. If our blood is increasing or decreasing in circulation, then that also will affect how much blood gets to the brain, which would affect memory. Without blood (which carries oxygen) the brain cannot function properly.

The last thing I will say here is that, we don’t know if weed CAUSES less brain activation or if people with less brain activation smoke weed more often. It very well could be the other way around and people that already have worse memory (and other anterior cingulate and thalamus functions) may use weed more.

I’ll keep these next 2 sections short (mainly because there isn’t too much research on it yet.

THC use:

When it comes to cannabis, there are 2 main ingredients: Tetrahydrocannabinol (THC; generally related to the hallucination/visual aspects of weed) and cannabidiol (CBD; generally for more relaxant functions of weed).

THC may be the reason why memory tends to be worse for weed users. When people are injected with a dose of THC, they have worse learning outcomes and are unable to understand what is a novel or new thing compared to something they already know. When you don’t know if something is novel, your brain won’t spend the extra resources or pay extra attention to it, so it won’t get encoded into memory, and it is harder to remember it.

CBD use:

Just like you can have THC alone, you can also have CBD alone. However, unlike THC, CBD actually may have some benefits to memory.

But! The improvement to memory may only happen if you already have a memory deficit of some sort. If you have good memory already, it likely does nothing.

Another thing is…this research was done on rats. I don’t know of any human studies looking at CBD and memory.

Outstanding questions:

1. What about other ways of ingesting weed? We don’t know. We literally don’t know. Hopefully there is more research soon because people are using weed regardless.

2. Does weed actually do anything to memory. We don’t know. As far as I know, there are no, what I would call, “good” studies on this. Everything deals with rather unimportant memory. If you see 10 random pictures and are asked to recall what the 5th picture is, people in general won’t care, let alone if you are high.

What about the important stuff? What about what Clarice said while you were having a personal and emotional discussion during a smoke session? What about what you and Karan discussed about the cure to cancer? Do we remember these details about ourselves and others any better or worse? What about working through problems—does that get impaired when it is something actually consequential and we are motivated to remember?

3. Is weed good or bad? Stop asking this. It depends. It depends on what you are talking about. Is it good for memory? Sometimes. Is it good for relaxing? Sometimes. Is it good for reducing anxiety? Sometimes. Is it good to help socializing? Sometimes. Is it good for me? Sometimes. Is it good for you? Sometimes. Like, stop it.

To be blunt, I think we can roll up this discussion at this point. The whole thing is pretty half-baked, but in time we’ll see how high we can take our memory systems.

Until next time.


Citation: Morie, K. P., & Potenza, M. N. (2021). A mini-review of relationships between cannabis use and neural foundations of reward processing, inhibitory control and working memory. Frontiers in psychiatry, 12, 546.

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