Marijuana use may hurt intellectual skills in MS patients

March 28, 2011

Any possible pain relief that marijuana has for people with multiple sclerosis (MS) may be outweighed by the drug's apparent negative effect on thinking skills, according to research published in the March 29, 2011, print issue of Neurology, the medical journal of the American Academy of Neurology.

Some clinical trials have reported a mild benefit of on pain, bladder dysfunction and spasticity in MS, an auto-immune disease that affects the brain and spinal cord.

The researchers studied two groups of 25 people each between the ages of 18 and 65 with MS. One group used marijuana and the other reported no marijuana use for many years. Urine tests were used to confirm use or non-use of the drug. The groups were matched so there would not be significant differences due to age, gender, level of education, IQ before diagnosis, level of disability and duration of time with MS.

On average, the duration of marijuana use was 26 years. A total of 72 percent of users reported on a daily basis while 24 percent reported weekly use and one person reported bi-weekly use.

Participants' were tested. The research found that people who used marijuana performed significantly worse with respect to attention, speed of thinking, executive function and of spatial relationships between objects. For example, on a sensitive test of information processing speed, those using marijuana scored approximately one third lower than non-users. Those who used marijuana were also twice as likely as non-users to be classified as globally cognitively impaired, defined as impairment on two or more aspects of intellectual functioning.

"Given that about 40 to 60 percent of have problems with cognitive function to begin with, any drug that may add to this burden is cause for concern," said study author Anthony Feinstein, MPhil, MD, PhD, with Sunnybrook Health Services Center and the University of Toronto in Ontario, Canada. "This study provides empirical evidence that prolonged use of inhaled or ingested marijuana in MS patients is associated with poorer cognitive performance, and these effects have to be weighed against any possible benefit of using marijuana for medicinal purposes."

Explore further: Conservative county OKs medical pot

Related Stories

Conservative county OKs medical pot

July 18, 2007

Conservative Orange County, Calif., will license the use of medical marijuana and issue ID cards to patients entitled to use it.

Smoking marijuana impairs cognitive function in MS patients

February 13, 2008

People with multiple sclerosis (MS) who smoke marijuana are more likely to have emotional and memory problems, according to research published February 13, 2008, in the online edition of Neurology, the medical journal of ...

Recommended for you

How the finch changes its tune

August 3, 2015

Like top musicians, songbirds train from a young age to weed out errors and trim variability from their songs, ultimately becoming consistent and reliable performers. But as with human musicians, even the best are not machines. ...

Shaving time to test antidotes for nerve agents

February 29, 2016

Imagine you wanted to know how much energy it took to bike up a mountain, but couldn't finish the ride to the peak yourself. So, to get the total energy required, you and a team of friends strap energy meters to your bikes ...

Machine Translates Thoughts into Speech in Real Time

December 21, 2009

( -- By implanting an electrode into the brain of a person with locked-in syndrome, scientists have demonstrated how to wirelessly transmit neural signals to a speech synthesizer. The "thought-to-speech" process ...


Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (4) Mar 28, 2011
Were they testing these people while the subjects were under the influence and then later when they were not?

For those with chronic use, did they test them again after a week of abstinence to measure any change in perceived intellect? One more incomplete study to toss on the pile.
2 / 5 (4) Mar 28, 2011
Who would have thought that marijuana use hurt cognitive skills?
4 / 5 (3) Mar 28, 2011
Apples to oranges. Pain decreases cognition, also.
5 / 5 (2) Mar 28, 2011
Simonsez: to answer your Qs, another article on this (on reuter i think) answered this. the patients in the study were off the stuff for at least 12 hours (so sort of a next-day effect kind of thing). which is what's relevant to patients anyway since that's their day to day functioning. if they quit for a long time, the results might be different - but less important for patients, who don't want to have to stop using it (for fear of symptoms coming back) just to get their thinking back the way it was.
also, every study is incomplete. no one study can look at every possible thing involved. things are complicated with humans. other studies should look at the longer term effects though in non-MSers, for those of us (non-MSers) who don't HAVE to keep using like MS patients.
5 / 5 (1) Mar 28, 2011
Pot use affects the thinking skills of any user. The issue is balancing the benefit vs the perceived cost.
3 / 5 (1) Mar 29, 2011
Pot use affects the thinking skills of any user. The issue is balancing the benefit vs the perceived cost.

This is correct, as current studies have shown that cannabis use will increase brain activity, cognition, and retention. It also staves off the effects of Alzheimers, and has been show to help stimulate the growth of new brain neurons with synapses (not just dormant neurons).

3 / 5 (1) Mar 29, 2011
Do you have the refs for these studies? or are these your personal opinions?
I ask cause most people come up with random views based on whatever works for them and then try to pass them on as evidence by saying studies have shown... without actually saying which studies; personal opinion is NOT evidence, so I was just wondering which studies these were, where were they published and who the authors are; if you're mentioning info based on EVIDENCE then we should all be able to locate the studies.
I'm not as interested in synaptic studies since those are at early stages and can't be translated into human function. But "staves off the effects of Alzheimers" and "increase brain activity, cognition, and retention"? Please provide refs (unless you personally decided to believe these things and spread them as facts)
btw increased brain activity can be detrimental-depends on where/when.brain hyperactivity does not always equal better function(check any neuro text-NOT random blogs)
5 / 5 (1) Mar 30, 2011
Who would have thought that marijuana use hurt cognitive skills?

So do some of the various non-narcotic medications for MS.

Would you rather repeatedly and uncontrollably wet your pants during a back spasm in public, or would you rather it took you an extra few seconds to remember where you left your keys?

I'd pick the latter, but to each their own.

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.