Marijuana unfairly blamed for effects of ‘use’

MarijuanaOur love-hate relationship with this seven-pointed leaf has been going on for decades. In fact, marijuana was in the top five most controversial topics of 2014. And while it continues making headline, behind laboratory doors scientists are changing the way they study the effect of this popular ingredient on our brains, which in turn might change the way we view this ‘weed’.

Until a few months ago, researchers generally avoided recruiting tobacco users for their participant pool, but in a recent study, scientists at the Center for Brain Health at the University of Texas in Dallas, observed significant differences between the brains of individuals who use both tobacco and marijuana and the brains of those who only use marijuana. These results are prompting them to question the correlation, and move away from the current practice.


Details of the study can be found in the online version of the journal Behavioral Brain Research.

For the study, the participants were selected based on their marijuana and tobacco usage and divided into these four groups:

1) Nonusers – people who have not touched marijuana or tobacco in the past 90 days
2) Chronic marijuana users – people who use marijuana at least four times per week
3) Frequent nicotine users – those who smoke 10 or more times daily
4) Chronic marijuana and frequent nicotine users

The researchers used MRI screening to examine the hippocampus, which is an area in brain linked to learning and memory and is known to alter in shape and size with chronic marijuana use.

In their study the scientists found that the size of the hippocampus decreases in both the marijuana only group and the marijuana and tobacco group when compared to the non-user group and tobacco only group. However, in regards to memory, the relationship between the groups was quite unique.

  • The non-user group – the smaller the hippocampus, the poorer the memory function
  • The marijuana and tobacco group – the smaller the hippocampus, the greater the memory
  • The tobacco only group and the marijuana only group – the size of the hippocampus did not affect the memory

The team also observed that the more cigarettes the marijuana and tobacco group smoked, the smaller the hippocampus became and the more memory performance improved.

According to the lead researcher, Francesca Filbey, Ph.D., who is also the Director of Cognitive Neuroscience of Addictive Behaviors at the Center for Brain Health, most studies trying to find the effects of marijuana do not take tobacco use into consideration. However, at least 70 percent of marijuana users are also tobacco users – a ‘blunt’ is wrapped in tobacco leaf while a ‘spliff’ is a joint rolled with tobacco – so the findings of these studies do not reveal the true effect of marijuana on the majority of the marijuana using population.


The study by Filbey’s team is the first of its kind to analyze both the unique effects of each substance on the brain and their combined effects.

The results of the study confirm that the interaction between marijuana and nicotine is much more complex, due to the various mechanisms at play. To get a clear picture of the effect of marijuana on memory function and behavior, more studies need to be done to address the compounding effects of substances.


Author Bio

Mohan Garikiparithi got his degree in medicine from Osmania University (University of Health Sciences). He practiced clinical medicine for over a decade before he shifted his focus to the field of health communications. During his active practice he served as the head of the Dept. of Microbiology in a diagnostic centre in India. On a three-year communications program in Germany, Mohan developed a keen interest in German Medicine (Homoeopathy), and other alternative systems of medicine. He now advocates treating different medical conditions without the use of traditional drugs. An ardent squash player, Mohan believes in the importance of fitness and wellness.