How does Marijuana affect memory?


By David Joel Miller.

Does Marijuana use result in State Dependent Learning?

In a previous post, I wrote about the concept of State Dependent Learning (SDL), how things learned while you have a drug in your bloodstream may be better remembered when you have that same drug in your body. Readers have asked if Marijuana use results in SDL and what other effects does marijuana have on memory?

If Marijuana causes state Dependent Learning then we should advise people who learn things while smoking Weed to also smoke weed while or shortly before needing to use that information.

Will smoking marijuana just before a test help students who smoke while studying remember the facts better for the test?

Clearly, a great many things, mood states, drugs in the system, even the general health of the individual can affect memory. Unbiased information about the precise effects of Marijuana on memory and learning has been difficult to find.

There are a number of reasons for the contradictory reports of health benefits and harms of Marijuana we read in the media. I have been reading the research since my last post on SDL and here are some of the things that I have found.

Marijuana is more like a stew than a vegetable.

Marijuana contains over 600 chemicals including 60 to 70 Cannabinoids (another article listed 116). Two of the Cannabinoids have some research data but a lot of the other chemicals are poorly understood and have little research. All of the possible combinations of these 600 chemicals create unlimited possibilities for effects. That is not the only reason we know so very little about the effects of marijuana on memory.

How does it work?

For a long time, we knew that marijuana was doing something, we just could not find any receptors for the Cannabinoids in the nervous system so we did not know exactly what Marijuana was doing to the nervous system. Starting in the late 1980’s and the early 1990’s receptors for Cannabinoids were found. But there are multiple kinds of receptors and they are located in some parts of the body and not others.

Many of the nerve cells that make up our “brain” are not in the head. When you are hungry the nerve cells in your stomach tell your brain that the stomach wants food. The same thing happens with Cannabinoids. Many of the Cannabinoid receptors are located in places like the spleen and the tonsils. So marijuana might affect memory for pain in the throat differently than memory for the history test.

Worse yet as we study the various Cannabinoids they don’t all do the same things. The two most widely studied Cannabinoids delta-9-tetrahydrocannabinol (THC) and Cannabidiol (CBD) appear to do opposite things. THC seems to produce thinking distortions. The younger you start using THC the more likely you are to develop psychosis. CBD, however, has been proposed and tested as a treatment for psychosis.

One theory, on this contradiction, postulates that young marijuana plants have more CBD and less THC. As the plants mature they form more THC and the CBD is reduced. So if there is high THC, which is the Cannabinoid that gets you high, then it has low medicinal properties. Plants with lots of CBD and that might be more medicinal don’t get you high. But most medical marijuana users want the kind that gets them high. What the other Cannabinoids are doing we are not really sure.

It depends on who makes the stew and how long you cook it.

One other problem with the research on Marijuana is that the concentrations of all the chemicals change depending on how the Marijuana is grown and how it is processed or dried after harvest. Various studies on Marijuana may really be studies of all sort of different chemicals, not just the Cannabinoid.

Recent research has tackled this problem by using pure synthetic Cannabinoids so when testing THC or CBD that is the only chemical being tested.

There are different types of memory and memory operations.

Short term memory is info that is held in memory for a minute or less. Drugs, emotions even attention can interfere with the ability to take in information. Ever read something in a book and a second later realize you don’t remember what you read? This is a failure to encode information into short-term memory.

Marijuana, particularly THC, has been implicated in the failure to encode the information.

Working memory is information being processed. Some information can be distorted while in processing by the drugs in the system. Alcohol especially can make the drunken person think things are happening that in fact did not happen.

I have not found studies that suggest that marijuana (THC) is altering information processing but it is altering some other memory events.

Long term memory is information held in storage.

Inability to find, access and retrieve information is what State Dependent Learning is all about. With SDL it is easier to retrieve previously stored information when the drug that was present during storage is again present.

Marijuana use has not been shown to affect memories formed prior to the use of the Marijuana. It is not likely to help reduce PTSD symptoms or unpleasant memories of the past for more than a short time period.

So far no studies I have found indicate that THC improves the ability to locate material that was previously stored.

Retrieval is the ability to find and pull up information.

If the information that you retrieve is inaccurate or incomplete this is a retrieval error.

THC appears to reduce the encoding of information so less gets into short-term memory and less is stored away.

THC is also reported to interfere with retrieval of information.

Smoking marijuana while studying results in learning less. Smoking marijuana just before taking the test interferes with remembering what was learned.

Marijuana use (THC) does not create State Dependent Learning and further use will not help recover memories of information learned while under the influence of marijuana.

There are plenty of people who smoke a lot of Marijuana and remember things just fine and there are people who do not smoke weed and have a poor memory, clearly smoking or not is not the whole answer.  But smoking weed has not been shown to improve memory or help retrieve previously learned information. It has been shown to interfere with encoding and decoding of information.

Under the influence of THC, you will learn and remember less than you would without the weed.

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For more about David Joel Miller and my work in the areas of mental health, substance abuse and Co-occurring disorders see the about the author page. For information about my other writing work beyond this blog check out my Google+ page or the Facebook author’s page, up under David Joel Miller. Posts to the “books, trainings and classes” category will tell you about those activities. If you are in the Fresno California area, information about my private practice is at counselorfresno.com. A list of books I have read and can recommend is over at Recommended Books

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2 thoughts on “How does Marijuana affect memory?

  1. Pingback: High Free Marijuana? | counselorssoapbox

  2. Pingback: How much does marijuana effect memory? | counselorssoapbox

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