Does Weed Kill Brain Cells? And 5 Other Things to Know
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.
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.
Researchers haven't determined whether smoking weed kills brain cells, but that hasn't stopped some groups from comparing the substance to nicotine and alcohol, two established brain cell killers. Here's what the science actually says about marijuana's effects on the brain, which users are most at risk, and more.
The key takeaway? More research needs to be done to understand how marijuana use affects intelligence over time.
CBD May Protect Against and Relieve Brain Injury Symptoms
During the past several years, public awareness about brain injuries has increased — thanks in part to several former professional athletes, military veterans, and accident survivors who are speaking out about effects of brain injuries, as well as a variety of brain injury awareness campaigns conducted by athletic and government organizations. 
Researchers also have been conducting studies to learn more about brain injuries, so they can understand the causes and develop new, more effective treatments. One brain injury treatment that is showing promise is cannabidiol, or CBD, which is a non-intoxicating cannabinoid molecule produced by cannabis.
What is a brain injury?
Traumatic brain injury (TBI) is a condition that occurs when a head injury, such as a bump, blow, or jolt, causes your brain to slam into the inside of your skull, which results in brain damage.
When your brain is injured, it releases neurotransmitters and chemicals that cause inflammation, blood vessel injury, chemical imbalances, tissue damage, and cell death. These brain responses are called a “secondary injury cascade” and are responsible for many of the neurological problems associated with TBI.
Although a severe TBI can be deadly or cause lifelong complications, even a mild TBI — which is commonly called a concussion — can cause symptoms that can last for days or weeks.
Repeated TBIs can cause a buildup of Tau protein, which can lead to a degenerative neurological condition called chronic traumatic encephalopathy (CTE). CTE can have a devastating impact on individuals and their families because it can cause a variety of symptoms that affect memory, emotions, behavior, movement, and mental functioning.
CBD May Offer Neuroprotective Benefits
In 1998, researchers published the results of a study on rats that demonstrated the neuroprotective benefits of CBD and tetrahydrocannabinol (THC), which are two of the cannabinoids found in cannabis.  Although more research is required to fully understand the neuroprotective effects of CBD, recent studies have shown that CBD activates the cannabinoid receptors in your brain that are part of your body’s natural endocannabinoid system.
A 2011 study of mice found that endocannabinoid levels are elevated during and after a TBI, which suggests that the endocannabinoid system plays an important neuroprotective role. 
Other animal studies also have shown that activating the cannabinoid receptors in your brain may help to limit nerve cell damage and promote healing by enhancing blood flow to the brain.  In a 2002 study, researchers found that mice that were genetically engineered to lack CB1, a cannabinoid receptor found in the brain, had more severe brain damage and cognitive deficits after a TBI when compared to mice that had the CB1 receptor.
Activating another cannabinoid receptor in the brain, called CB2, has been shown to promote the creation of new brain cells, as well as regulate inflammation after brain injury. A 2014 animal study found that mice that were genetically engineered to lack a CB2 receptor had worse outcomes after TBI when compared to mice that had a CB2 receptor. The study also found that the lack of a CB2 receptor impaired the creation of new brain cells.
And, CBD may also affect your glial cells, which insulate your neurons and facilitate your brain’s immune response after injury. Research shows that CBD seems to have the strongest effect on two types of glial cells: astrocytes and microglia. A 2017 animal study showed that CBD suppressed the activity and swelling caused by astrocytes;  another 2017 study showed that stimulating cannabinoid receptors in the brain suppressed inflammation caused by microglia in rats.
The Benefits of the “Entourage Effect”
Because full-spectrum CBD contains a variety of phytocannabinoids, it produces an “entourage effect” that engages both the CB1 and CB2 receptors in the brain — as well as other cannabinoid and non-cannabinoid receptors throughout your body — for maximum neuroprotective and overall health benefits.
Although further research is needed, some studies suggest that when CBD is used shortly before or within 12 hours of a brain injury, it may help to prevent or limit the damage that occurs after a TBI during the secondary injury cascade.
Anecdotal Evidence and Research Support CBD Use for TBI and CTE
Although CBD has shown promise for brain injury treatment in the research lab, anecdotal evidence also is strong — especially among some former professional athletes in sports with a high risk of head injuries, such as boxing and football.
Many professional athletes have spoken out about the benefits of CBD for the treatment of TBI and CTE symptoms, saying that it helped to regulate their mood, improve physical function, and reduce or eliminate their use of prescription painkillers and other medications.
Unlike many prescription pain medications, CBD is non-addictive and will not lead to overdose. CBD does not cause side effects and will not result in increased tolerance that requires higher doses to achieve the same effect. CBD also can be used to treat other health conditions that are common in athletes, such as chronic pain, anxiety, and insomnia.
But although anecdotal evidence suggests that CBD may be safe and effective for professional athletes, it also may show promise for the treatment of TBIs caused by youth sports, falls, car accidents and military combat injuries. And, researchers are investigating CBD as a potential treatment for other conditions that affect the brain, including Alzheimer’s disease, Parkinson’s disease, stroke, and HIV-associated dementia.
Researchers are hoping to conduct further studies on CBD and how it can be used to treat TBI and CTE, as well as develop dosing and safety recommendations for CBD use. But in the meantime, many people who have experienced TBI or have been diagnosed with CTE are using CBD to treat the symptoms of their condition — often with life-changing results.During the past several years, public awareness about brain injuries has increased — thanks in part to several former professional athletes, military veterans, and accident survivors who are speaking out about effects of brain injuries, as well as a variety of brain injury awareness campaigns conducted by athletic and ]]>