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Nicotine changes marijuana’s effect on the brain

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.”

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 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.

What Happens If You Smoke Marijuana?

Reactions with pot can vary widely

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Steven Gans, MD is board-certified in psychiatry and is an active supervisor, teacher, and mentor at Massachusetts General Hospital.

Sean Gallup Collection / Getty Images News

The reaction you may have when trying marijuana can vary dramatically based on many factors.   Some people report not feeling anything at all when they smoke marijuana. In other cases, people report feeling relaxed or “high.”

Some people who use marijuana report having sudden feelings of anxiety and paranoid thoughts and that might be caused by trying a higher potency marijuana, according to the National Institute on Drug Abuse.  

Research also shows that regular use of marijuana is linked to an increased risk of depression, anxiety and a loss of motivation or drive.   You may feel “dopey” on the drug, which is when you begin to lose interest in activities that you might have previously enjoyed or you may lose the ability to grasp concepts easily.

Short-Term Discomforts of Using Weed

The effects of using marijuana can be unpredictable, especially when it is mixed with other drugs, research shows. You may feel relaxed on the drug, but other things you might not be expecting with pot use can include rapid heart rate and other unpleasantries.  

  • Dry mouth
  • Swollen eyelids
  • Bloodshot eyes
  • Loss of coordination
  • Accelerated heart rate

Short-Term Hazards

As with any drug or substance that can alter perception, logic and usual behavior, there are several short-term hazards of using marijuana from impairing driving abilities to memory loss.  

  • Learning difficulties
  • Lack of attention and focus
  • Poor driving skills
  • Anxiety and paranoia
  • Impaired memory
  • Difficulty in thinking

Long-Term Hazards

Any drug that is taken over a prolonged period of time can have an effect on your health. Several of the physical barriers that can occur range from infertility problems to overall brain functions.  

  • An increased risk of developing lung, head, and neck cancers
  • Lack of motivation
  • Decreased sperm count in men
  • Irregular menstruation in women
  • Respiratory problems
  • Heightened risk of infections, especially the lungs
  • Poor short-term memory recall
  • Inability to shift attention normally
  • Inability to understand complex information​

Unpredictable Reactions

The National Institute on Drug Abuse reports that marijuana can affect each person differently according to their own body chemistry and the type of pot used.   Some people can use weed and never have any negative reactions while others may try it and get entirely freaked out by the experience.

  • Your biology (genetic makeup)
  • Marijuana’s strength (amount of active ingredient THC)
  • Previous experience with the drug
  • How it’s taken (smoked versus ingested)
  • Whether alcohol or other drugs are taken too​

Not Your Grandfather’s Pot

Studies have found that the marijuana available today is much different in terms of potency compared to what was generally available in the 1960s when the use of the drug became widespread in the United States.  

Today’s strains of the plant contain much more of the active ingredient in marijuana: tetrahydrocannabinol or THC, researchers say.   That makes today’s weed much more potent than that smoked by the hippies and flower children of the Woodstock generation.

How marijuana affects the individual user depends on many different factors, including body chemistry and the potency of the drug.