The Effects of Marijuana on Cognitive Functioning

Psychology 20, Spring 2000

April 19, 2000

By: Stephanie Nunley, Brooke Alexander, Rachel Corns and John Geer

 

The Effects of Marijuana on Cognitive Functioning

It may not seem like much of a question to ask whether or not smoking marijuana has an affect on a userís cognitive functioning. However, with the recent debate over the possible medical applications and benefits of smoking marijuana to relieve pain and discomfort stemming from various impairments, this question proves to be a very logical and useful topic to research. The following information will seek to understand what marijuana is and how it affects the brain and various cognitive functions.

General Information: What are the general facts about marijuana?

Myths: What are the untruths about marijuana use?

Fact: Research by Dr. Alan Searleman of St. Lawrence University has shown that people who smoked marijuana in their past forget just as much information as people who have never smoked

Fact: Less than one percent of users consume marijuana on a daily basis and an even smaller percentage actually develop a dependence on marijuana

Fact: Research shows that there is no possibility of a fatal overdose resulting from marijuana usage no matter what the amount of THC may be

Physiology: How does marijuana affects the brain?

A Study on the Cognitive Impairments of Heavy Marijuana Users

Conducted by Dr. Pope and Dr. Block of the NIDA

According to an NIDA-funded study, students who smoke marijuana heavily may be limiting their ability to learn. College students who used marijuana regularly had impaired skills to attention, memory, and learning 24 hours after they had last used the drug.

-65 heavy cannabis users, most of whom had smoked marijuana at least 27 out of the previous 30 days (18-24 years of age)

-64 light cannabis users, most of whom had smoked marijuana on no more than 3 of the previous 30 days (18-28 years of age)

-Subjects of both groups had smoked marijuana for at least 2 years, but none for a decade

To ensure that the subjects did not smoke marijuana or use other illicit drugs or alcohol during the study, the researchers monitored them for 19 to 24 hours. Then the subjects performed an array of standard test designed to assess their ability to pay attention, learn, and recall new information. Some of the tests included learning lists of words and sorting cards by different characteristics such as color and shape.

The tests indicated that heavy users had more difficulty than light users in sustaining and shifting attention and hence in registering, organizing, and using information. Heavy users exhibited these cognitive deficits by being less able to learn the word lists and also making a large number of errors when sorting the cards.

The diminished ability to pay attention and decreased mental flexibility exhibited in these tests may cause chronic marijuana users important difficulties in adapting to intellectual and interpersonal tasks. However, it remains unclear whether marijuanaís short-term residual cognitive impairments are due to either a residue of the drug that remains after use or to a neurotoxic effect of the drug on the brain structure or function.

"This is a fairly definitive study because it was methodologically sound and controlled for a wide number of factors, including the possible confounding effects of alcohol and other drug use," says Dr. Jagjitsing Khalsa of NIDAís Division of Clinical and Services Research.

"Now we know that for students who smoke marijuana heavily, the ability to learn is affected not just while they are high, but for at least a day after," says NIDA Director Dr. Alan I. Leshner.

 

The Effects of Marijuana on Long and Short Term Memory

An experiment conducted by Charles T. Tart, Ph.D.

The following statements were asked of marijuana users with the following responses:

"My memory for otherwise forgotten events is much better than when straight when I consciously try to remember."

Results: fairly frequent which begins to occur at moderate to strong levels of intoxication

"My memory for otherwise forgotten events is much worse than when straight when I try to remember."

Results: Also occurs at moderate to strong levels of intoxication

"I spontaneously remember things I hadnít thought of in years, more so than straight (does not apply to consciously trying to remember things)."

Results: More frequent among young users, begins to occur at strong levels of intoxication

The following statements were asked of marijuana users with the following responses:

"My memory span for conversations is somewhat shortened, so that I may forget what the conversation is about even before it has ended (Even though I may be able to recall it if I make a special effort)."

Results: Begins to occur at strong to very strong levels of intoxication. Heavy users need to be more intoxicated to forget the start of the conversation.

"My memory span for conversations is very shortened, so that I may forget what the start of a sentence was about even before the sentence is finished (although I may be able to recall it if I make a special effort)."

Results: This drastic shortening of memory span begins to occur at the strong and very strong levels of intoxication

"I can continue to carry on an intelligent conversation even when my memory span is so short that I forget the beginnings of what I started to say; e.g., I may logically complete a sentence even as I realize I have forgotten how it started."

Result: This effect begins to occur at the strong and very strong levels of intoxication. The weekly users responded with higher levels of agreement to this statement than the daily users.

There is often an increasing shortening of intermediate- and short-term memory span with increasing levels of intoxication, as much as forgetting the start of a sentence when one is speaking at strong and very strong levels. But it is commonly felt that this does not necessarily have any affect on the intelligibility of the users conversation. These experiments show that marijuana does in fact have an impact on the memory depending on the amount of usage and level of intoxication.

Group Conclusion

After doing research to determine whether or not marijuana affects cognitive processes, we conclude that in fact marijuana does have detrimental affects on the brain and cognitive functioning. Specifically it affects short-term memory, long-term memory, and the ability to learn. Studies have helped to provide evidence that chronic use of marijuana can permanently damage regions of the brain, especially the hippocampus and cerebellum.