Study links cannabis strains with memory impairment

October 1, 2010, University College London

Study links cannabis strains with memory impairment
(PhysOrg.com) -- People who smoke potent strains of cannabis that are low in cannabidiol (such as skunk) are putting themselves at far greater risk of acute memory loss than people who smoke other types of the drug, according to new research published in the October issue of the British Journal of Psychiatry.

Now the study’s authors are calling for cannabis users to be made aware of the risks associated with using some strains of cannabis - and encouraged to use strains with higher levels of cannabidiol instead.

Two major constituents of cannabis are Δ9-tetrahydrocannabinol (THC) and cannabidiol. THC is the main psychoactive ingredient which makes users feel ‘stoned’, and produces psychotic-like symptoms such as delusions and paranoia. In contrast, cannabidiol does not induce these symptoms and may counteract the effects of THC. Levels of cannabidiol in cannabis can range from virtually none, to up to 40 per cent.

The UCL researchers tested 134 cannabis users aged between 16 and 23 years. The participants were invited to take a series of memory tests on two separate occasions - once while they were smoking their own preferred type of cannabis and were intoxicated, and once when they had not smoked for the last 24 hours and were sober.

A sample of the cannabis each participant smoked was taken on the intoxicated day and analysed for levels of THC and cannabidiol. Saliva samples were also taken from each participant, and analysed for levels of THC and cannabidiol.

The researchers found that people smoking cannabis containing a low percentage of cannabidiol performed much worse on the memory tests when they were intoxicated than when they were sober. In contrast, those smoking cannabis high in cannabidiol performed just as well on the tests when they were intoxicated as when they were sober. There were no differences in the THC content of the cannabis smoked by any of the participants.

Professor Valerie Curran, UCL Psychology, said: “We asked the participants to recall a short passage of prose, immediately after hearing it and again after a short delay. We found that people who were smoking cannabis low in cannabidiol experienced memory impairment and remembered less of the prose that they could when sober. However, people who were smoking high cannabidiol strains were still good at these tests. Indeed, their performance when intoxicated was virtually indistinguishable from when they were drug-free.

“Over the last 20 years, the constituents of street have changed, with low-cannabidiol strains like skunk now dominating the market. But our study suggests that these strains can increase the risk of cognitive harm. On the back of this study, we believe users should be made aware of the risk of from smoking low-cannabidiol strains. They should be encouraged to use strains containing higher levels of cannabidiol instead.”

More information: bjp.rcpsych.org/

Related Stories

Recommended for you

Study shows how bias can influence people estimating the ages of other people

October 17, 2018
A trio of researchers from the University of New South Wales and Western Sydney University has discovered some of the factors involved when people make errors in estimating the ages of other people. In their paper published ...

Infants are more likely to learn when with a peer

October 16, 2018
Infants are more likely to learn from on-screen instruction when paired with another infant as opposed to viewing the lesson alone, according to a new study.

Researchers use brain cells in a dish to study genetic origins of schizophrenia

October 16, 2018
A study in Biological Psychiatry has established a new analytical method for investigating the complex genetic origins of mental illnesses using brain cells that are grown in a dish from human embryonic stem cells. Researchers ...

Income and wealth affect the mental health of Australians, study shows

October 16, 2018
Australians who have higher incomes and greater wealth are more likely to experience better mental health throughout their lives, new research led by the Bankwest Curtin Economics Centre has found.

Study suggests biological basis for depression, anxiety, sleep disturbances in older adults

October 15, 2018
UC San Francisco researchers, in collaboration with the unique Brazilian Biobank for Aging Studies (BBAS) at the University of São Paulo, have shown that the earliest stages of the brain degeneration associated with Alzheimer's ...

Linguistic red flags from Facebook posts can predict future depression diagnoses

October 15, 2018
In any given year, depression affects more than 6 percent of the adult population in the United States—some 16 million people—but fewer than half receive the treatment they need. What if an algorithm could scan social ...

4 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

jerryd
not rated yet Oct 02, 2010

The study does not indicate harm, just short term memory loss which in under 24hrs, likely under 4 hrs, goes away.

For some it is the reason to smoke, to forget about how hard one's day has been and just relax.
JamesThomas
5 / 5 (3) Oct 02, 2010
I was going to comment, but don't recall what I was going to say...
Skeptic_Heretic
3 / 5 (2) Oct 02, 2010
once while they were smoking their own preferred type of cannabis and were intoxicated, and once when they had not smoked for the last 24 hours and were sober.

Their readings were rather horridly skewed if this was the case. Your body doesn't metabolize THC entirely in that short a period of time while other cannabinoids not named in the article are metabolized within hours. There's too much noise in this study, especially with a "bring your own" basis for it.
TAz00
not rated yet Oct 08, 2010
I would like to buy the test they used, so I can test my own strains and improve :)

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.