Dr. David Pompei, PharmD, MS
As a cannabis user, you've undoubtedly heard the rumors that weed kills brain cells. But is there any truth to this claim? Or is it just another urban legend? We'll take a look at the evidence – both scientific and anecdotal – to find out whether or not weed damages our brains. Spoiler alert: the answer isn't entirely clear-cut, but it seems that weed probably doesn't have a major impact on overall brain health. However, it's always important to be aware of the potential risks, so read on for more information about whether weed kills brain cells.
While there's evidence suggesting that cannabinoids could have neuroprotective effects, it's essential to consider the potential risks as well, especially for developing brains. In adolescents, whose brains are still in crucial stages of development, regular cannabis use has been associated with alterations in brain structures involved in memory and attention, and might even affect the timing and efficiency of brain development. It's vital for young people, their parents, and educators to be aware of these risks.
Many heavy cannabis users have short-term memory impairment. Is this because weed is bad for your brain? We will explore short-term memory impairment in heavy cannabis users below, but first let’s go over how cannabis affects your brain at a basic level.
Upon smoking or ingesting cannabis, THC attaches to cannabinoid receptors in the brain (particularly the CB1 receptor), which affects neurotransmitter transmission throughout the brain. For a deep dive on how cannabis affects your brain, check out our article on the endocannabinoid system.
Cannabis intoxication may make it difficult to concentrate and impair short term memory. Additionally, basic motor skills can be impaired, which is why driving while high is dangerous.
However, despite the cognitive impairment associated with cannabis consumption, scientists still disagree about marijuana's long-term effects on the human brain as many cannabinoids (notably CBD and CBG, but also THC) may have some neuroprotective effects.
According to 2020 research published in the journal Molecular Neurobiology, cannabinoids can activate healthy cellular processes like antioxidation instead of stimulating the cellular processes which cause cell death. For degenerative brain disorders like Parkinson's and Alzheimer's, cannabis and its derivatives are attractive therapeutic targets as they may have some positive effects on neurodegenerative diseases.
Additionally, an analysis published in Neurobiology of Aging in 2018 found that injections of THC at very low doses temporarily reversed the cognitive impairments associated with aging in older mice. During the seven-week period, the positive effects persisted. So cannabinoids can have varying effects on brain health and function, depending on your age and various other factors.
The process of neurogenesis involves the formation of new neurons in the brain. The development of an embryo relies heavily on neurogenesis, but it continues throughout thelifespan in specific regions of the brain.
For a long time, scientists thought that the central nervous system (the brain and spinal cord) could not regenerate or undergo neurogenesis. Adult neurogenesis is now accepted as a natural occurrence that occurs in healthy brains since the discovery of stem cells in adult brains in the 1990s.
Consequently, there is evidence to suggest that cannabis consumption could be beneficial in the aging process by generating new neurons for the brain and potentially slowing the onset of Alzheimer's, dementia, and other diseases of the brain.
Research by The University of Saskatchewan's Dr. Xia Zhang showed in 2005 that cannabinoids promote neurogenesis. After carefully examining the data, Dr. Zhang concluded, "most' drugs of abuse' suppress neurogenesis. Only marijuana promotes neurogenesis."
In 2013, Brazilian scientists expanded on this research, showing that CBD, another chemical in cannabis, also stimulates the growth of new brain cells. Furthermore, another 2013 study conducted by Italian researchers in the peer-reviewed journal Neurochemistry International produced the same result with cannabichromene (CBC), another neuroprotective cannabinoid present in cannabis resin.
Is there any truth to the idea that weed kills brain cells? It turns out that there are some studies that indicate that THC can induce apoptosis in neuronal cell cultures - which means that scientists have found that cannabinoids can induce cell death with in vitro experiments. Scientists have not found this pattern in experiments conducted on living animals.
In fact, researchers have found that “cannabinoid neuroprotection is more evident in whole-animal than in cultured-neuron models.” In short, the evidence suggests cannabis does not cause neuronal cell death in humans.
However, THC does affect neurons in the brain in some surprising ways. For example, the reason THC impairs short term memory seems to be that THC impairs the ability of neurons to convert nutrients into energy.
As Jointly discussed in our article on cannabis and memory loss:
Researchers discovered that there are CB1 receptors on the mitochondria of nerve cells, including on the mitochondria of nerve cells in the hippocampus. Mitochondria are organelles that exist in every complex cell, and serve a variety of purposes from turning sugar, fat, and protein into chemical energy, to recycling waste products, to playing a role in cell death (apoptosis).
The researchers determined that when you consume cannabis, THC activates CB1 receptors on the mitochondria in the hippocampus. This interaction alters mitochondrial activity and reduces cellular respiration, which is the process by which nutrients are converted to energy. Mice genetically engineered to lack CB1 receptors in the hippocampus did not experience memory loss from cannabis, confirming that this side effect is due to the presence of CB1 receptors in this region of the brain.
In conclusion, the idea that weed kills brain cells is a common misconception. While the effects of THC on the brain have been shown to impair short-term memory and concentration, there is evidence to suggest that marijuana consumption may not have a massive impact on brain health overall.
In fact, some research has shown that cannabinoids can have positive effects on the aging process and potentially slow the onset of neurodegenerative diseases. THC has been shown to induce cell death in neuronal cell cultures in vitro experiments, but no evidence has been found of this pattern in experiments conducted on living animals. In light of this, it is safe to say that cannabis does not kill brain cells.
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