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Nicotine changes marijuana's effect on the brain

  1. RoboCodeine7610
    How scientists study the effects of marijuana on the brain is changing. Until recently marijuana research largely excluded tobacco users from its participant pool, but scientists at the Center for BrainHealth at The University of Texas at Dallas have found reason to abandon this practice, uncovering significant differences in the brains of individuals who use both tobacco and marijuana and the brains of those who only use marijuana.

    In a study that appears online in the journal Behavioural Brain Research, scientists report an association between smaller hippocampal brain volume and marijuana use. Although the size of the hippocampus, an area of the brain associated with memory and learning, is significantly smaller in both the marijuana group and marijuana plus tobacco group compared to non-using controls and individuals who use tobacco exclusively, the relationship to memory performance is unique.

    Hippocampal size of nonusers reflects a direct relationship to memory function; the smaller the hippocampus, the poorer the memory function. Individuals who use marijuana and tobacco show an inverse relationship, i.e., the smaller the hippocampus size, the greater memory the function. Furthermore the number of nicotine cigarettes smoked per day in the marijuana and nicotine using group appears to be related to the severity of hippocampal shrinkage. The greater the number of cigarettes smoked per day, the smaller the hippocampal volume and the greater the memory performance. There were no significant associations between hippocampal size and memory performance in individuals who only use tobacco or only use marijuana.

    "Approximately 70% of individuals who use marijuana also use tobacco," explained Francesca Filbey, Ph.D., the study's principal investigator and Director of Cognitive Neuroscience of Addictive Behaviors at the Center for BrainHealth. "Our findings exemplify why the effects of marijuana on the brain may not generalize to the vast majority of the marijuana using population, because most studies do not account for tobacco use. This study is one of the first to tease apart the unique effects of each substance on the brain as well as their combined effects."

    Dr. Filbey's research team used magnetic resonance imaging (MRI) to examine the hippocampus; an area of the brain that is know to have altered size and shape in association with chronic marijuana use. Participants completed a substance use history assessment and neuropsychological tests three days prior to an MRI head scan. The team compared four groups: nonusers (individuals who have not had any marijuana or tobacco in the past three months), chronic marijuana users (individuals who use marijuana at least four times per week), frequent nicotine users (10 or more times daily) and chronic marijuana plus frequent nicotine users (at least four marijuana uses per week and 10 or more nicotine uses per day).

    "We have always known that each substance is associated with effects on the brain and hypothesized that their interaction may not simply be a linear relationship. Our findings confirm that the interaction between marijuana and nicotine is indeed much more complicated due to the different mechanisms at play," said Filbey. "Future studies need to address these compounding effects of substances."

    She continued, "The combined use of marijuana and tobacco is highly prevalent. For instance, a 'blunt' is wrapped in tobacco leaf. A 'spliff' is a joint rolled with tobacco. We really need to understand how the combined use changes the brain to really understand its effects on memory function and behavior."

    Center for BrainHealth.
    ScienceDaily, 18 August 2015.


  1. 5-HT2A
    How Tobacco Seems To Block Memory Loss For Pot Smokers

    [IMGR="WHITE"]https://drugs-forum.com/forum/attachment.php?attachmentid=45742&stc=1&d=1440592378[/IMGR]About 70% of pot smokers also use tobacco, and that sizeable population has typically been excluded from marijuana studies because researchers are, well, studying marijuana—not tobacco, and not marijuana and tobacco.

    But a new study from the University of Texas looks at pot smokers who also smoke cigarettes and it finds significant differences between those who smoke both and those who only smoke pot.

    Researchers at the university's Center for Brain Health were looking specifically at the size of the hippocampus—a brain region responsible for memory and learning—and found that while both cigarette smokers and pot smokers had smaller hippocampal brain volumes than non-smokers, people who smoked both showed signs of improved functioning.

    In people who use only one of the drugs, there was "no significant associations between hippocampal size and memory performance." In non-marijuana and -tobacco users, the size of the hippocampus has a direct relationship to memory function—the smaller the hippocampus, the poorer the memory function. But in people who use both substances, that relationship was flipped: The more cigarettes they smoked each day, the greater the hippocampal shrinkage, but also, and paradoxically, the greater the memory performance.

    "We would anticipate that an individual with small hippocampal volume would perform more poorly on a memory function task, but instead individuals in our study who use marijuana as well as tobacco demonstrated the reverse. The smaller the hippocampus size, the greater the memory performance," Francesca Filbey, the study's lead investigator, told ATTN.

    "Because existing studies have noted that nicotine's cognitive enhancing effects are observable only in those with the reduced memory performance, we speculate that we may be observing short-term cognitive enhancement as a result of nicotine use, that is especially greater in those with smaller hippocampal volumes," she added.

    "Our findings exemplify why the effects of marijuana on the brain may not generalize to the vast majority of the marijuana-using population, because most studies do not account for tobacco use," Filbey continued. "This study is one of the first to tease apart the unique effects of each substance on the brain as well as their combined effects."

    The study divided subjects into four groups: non-users, chronic marijuana users, frequent cigarette smokers, and chronic marijuana users who were also frequent cigarette smokers. They were given history assessments and neuropsychological tests and subjected to magnetic resonance imaging scans of their brains.

    It's not just the findings but the range of subjects that makes the study fairly unusual in the marijuana literature. And it could lead the way to more studies that try to assess the impacts of poly-substance use.

    "Research has primarily been dedicated towards determining unique effects of substances, which results in either excluding combined users or controlling for their effects through statistical means. But I think that it is equally important to determine combined effects of substances, particularly when it is so prevalent," Filbey explained.

    "This study is one of the first to provide evidence that the confounding effect of tobacco on marijuana use is significant. As the prevalence of marijuana use and its potency is rapidly increasing, so is the knowledge in the scientific community that individuals are very rarely using only one substance. We hope that our findings will really influence the way future studies on the effects of marijuana on the brain are conducted," she said.

    In the meantime, smoke 'em if you've got 'em. It may help you remember that you've got 'em in the first place.

    by Phillip Smith

    August 24, 2015

  2. detoxin momma
    Re: How Tobacco Seems To Block Memory Loss For Pot Smokers

    this is an interesting read.
    I smoke cigarettes and marijuana on a daily basis.
    and I've got one hell of a memory!
    I'd almost say photographic,once I see it,its etched in.

    in fact,i'd prefer to forget more often! some things don't need to be remembered.
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