As recreational marijuana use becomes legalized throughout the US, many people now wonder how marijuana affects the brain and whether or not it kills brain cells. Just as years of heavy alcohol, meth, and heroin use can cause some irreversible brain damage, prolonged marijuana abuse can affect the ability of brain cells to convey messages (also known as brain activity). Using marijuana can cause damage to brain cells that results in a number of concurrent symptoms throughout the body.

Like other drugs, components of marijuana bind with specific receptors in the brain. Tetrahydrocannabinol (THC) is marijuana’s primary psychoactive ingredient, and it attaches to the brain’s cannabinoid receptors (officially known as cannabinoid receptor type 1 or CB1). These receptors connect to nerves in the brain function which govern memory, appetite, pain regulation, and mood.

When a person smokes marijuana, they may notice they struggle with staying focused or recalling important details. This can worsen with prolonged marijuana use, resulting in problems like poor memory and concentration. Motor skills can also be affected by the drug. If someone decides to drive while high, they can endanger their lives and the lives of others.

At this time, scientists are not fully aware of the long-term effects of marijuana use and the brain. They have, however, found a correlation between children and adolescence who use marijuana regularly who grow up to have lower IQs due to their marijuana use. Therefore, exposure to THC as a child can cause changes in cognition and memory later on in life. Less research has been done or has found much on adults who begin using marijuana after the adolescent stage.

Is it possible?

does weed kill brain cells

We don’t know for sure if using marijuana can kill your brain cells.

More research is also needed to determine whether each form of use — including smoking, vaping, and ingesting edibles — has a different effect on your brain’s overall health.

Studies evaluating the cognitive effects of long-term marijuana use are ongoing.

Here’s what we currently know about how weed affects the brain.

What about that infamous IQ study?

A well-known 2012 study from New Zealand evaluated marijuana use and cognitive ability in more than 1,000 individuals over a 38-year period.

The researchers reported an association between ongoing marijuana use and cognitive decline.

In particular, they found that:

  • People who started using marijuana heavily as adolescents and continued as adults lost an average of six to eight IQ points by the time they reached midlife.
  • Among the group above, people who stopped using marijuana as adults didn’t regain lost IQ points.
  • People who started using marijuana heavily as adults didn’t experience any IQ loss.

This study had a significant impact for a few reasons.

First, it was among the first large, longitudinal (long-term) studies to assess marijuana use and cognitive functioning.

Next, the results suggest that marijuana use during adolescence may have an irreversible effect on adolescent brain development. Some additional research supports this conclusion.

However, the New Zealand study also has significant limitations.

For one, it isn’t possible to conclude that marijuana use causes lower intelligence based on this study alone.

While the researchers controlled for differences in participant education levels, they didn’t rule out additional factors that may have contributed to cognitive decline.

A 2013 reply to the New Zealand study suggests that personality factors may play a role in both marijuana use and cognitive decline.

The author cited conscientiousness as an example. Low conscientiousness might explain both drug use and poor performance on tests of cognition.

Genetic factors may also contribute to cognitive decline, as suggested by a longitudinal twin study from 2016.

In this case, the researchers compared changes in IQ between twins who used marijuana and their abstinent siblings. They didn’t find any significant differences in IQ decline between the two groups.

The key takeaway? More research needs to be done to understand how marijuana use affects intelligence over time.

Synthetic Marijuana’s Effect On The Brain

does weed kill brain cells

Synthetic marijuana, a man-made hallucinogenic substance typically sprayed onto plant material, is not safe for human consumption but has become popular in recent years. Also known as “fake weed,” it produces mind-altering affects and can cause the individual to act in an odd manner. Synthetic marijuana is illegal and may have toxic ingredients that can cause increased heart rate, unexplained bleeding, and vomiting.

Similar to marijuana, synthetic marijuana affects the brain by attaching itself to the cannabinoid receptor type 1 (CB1) found in both the central and peripheral nervous systems. Synthetic weed binds more strongly to CB1 receptors than THC, making it at least 100 times more potent in the brain. Because CB1 receptors have multiple locations in the brain, side effects can be intense and harmful.

Synthetic marijuana may cause the brain and body to experience:

  • Memory loss
  • Seizures
  • Psychosis
  • Cardiac and respiratory problems
  • Stroke
  • Paranoia
  • Hallucinations
  • Altered perception or euphoria
  • Violent behavior
  • Kidney and brain damage

In addition to the above symptoms, synthetic marijuana can be addictive to individuals who take it. Addiction, a chronic disease, can result in drug abuse that directly damages the brain, as well as risky behaviors that can cause further damage. After prolonged use of synthetic marijuana, brain cell activity is likely to decline with a concurrent increase in negative physiological symptoms like the ones above.

Short- and Long-Term Effects of Marijuana Use on The Brain

The immediate, short-term effects of marijuana use on the brain include:

  • Difficulty judging distances
  • Difficulty remembering
  • Fatigue
  • Confusion
  • Paranoia
  • Anxiety

Long-term effects include but are not limited to:

  • Some cognitive impairment
  • Some memory loss
  • Increased likelihood to use other drugs
  • Increasing marijuana tolerance
  • Marijuana dependence

‘Highly Effective Medicine’

“I just re-published a paper of the first survey for marijuana toxicity done in 1863 by the British government in India that was the most exhaustive medical study of its time in regards to possible difficulties and toxicity of cannabis. And it reached the same conclusion as Grant,” Mikuriya tells WebMD.

“This is merely confirming what was known over 100 years ago, as well as what was learned by various government findings doing similar research — marijuana is not toxic, but it is a highly effective medicine.”

In fact, marijuana was available as a medicinal treatment in the U.S. until the 1930s.

Lester Grinspoon, MD, a retired Harvard Medical School psychiatrist who studied medicinal marijuana use since the 1960s and wrote two books on the topic, says that while Grant’s finding provides more evidence on its safety, “it’s nothing that those of us who have been studying this haven’t known for a very long time.

“Marijuana is a remarkably safe and non-toxic drug that can effectively treat about 30 different conditions,” he tells WebMD. “I predict it will become the aspirin of the 21st century, as more people recognize this.”

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