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Addiction and Substance Abuse




Does cannabis kill or affect brain cells even after cessation of use?


This is an interesting question, and there is emerging research to suggest that this may be a possibility. But let me preface my answer with several comments.

We have only been studying the long-term effects of marijuana use for the past 30 years, as prior to that there was not a large group of people who had used marijuana to study. We have animal studies but we need to make sure these same results occur with humans. Bear in mind that results are for the group as a whole and vary by individuals. Research outcomes vary by the amount used, length of time used, and strength of the dose.

What we do know is that marijuana reduces learning ability. Increasingly, research indicates that marijuana limits the capacity to absorb and retain information. A 1995 study of college students discovered that the inability of heavy marijuana users to focus, sustain attention, and organize data persists for as long as 24 hours after their last use of the drug. Now here is the part you are questioning. In another study comparing cognitive ability of adult marijuana users with non-using adults, they found that users have decreased memory as well as math and verbal skills. We do not as yet have conclusive evidence that heavy marijuana use can cause irreversible loss of intellectual capacity; animal studies have shown marijuana-induced structural damage to portions of the brain essential to memory. So there is a possibility that we will find that marijuana use does have long term effects on the brain, especially related to thinking and memory.

Below are several good websites that will keep you up-to-date on what we are learning in this area. Remember to separate opinion from scientific research.

Marijuana: Brown University Health Education

Health Concerns: What are the Medical Dangers of Marijuana Use?

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Response by:

Janice Dyehouse, PhD, RN
Adjunct Professor
College of Nursing
University of Cincinnati