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Is it true that marijuana is bad for the brain?

marijuana bad for the brain

Much has been speculated about the effects of cannabis on the brain. Perhaps previously the approach was a bit biased because, at the time, when tetrahydrocannabinol (THC) was first isolated, it was not always possible to isolate the tetrahydrocannabinol (THC) was first isolated, there were high hopes for its therapeutic was isolated, there were high hopes for its therapeutic power.

Nowadays, due to the boom in genetic selection and the improvement of cannabis cultivation, marijuana has so much THC that its consumption may no longer be so beneficial for the organism. As we commented in a previous post, marijuana has gone from 4% to 35% THC in less than 30 years. . This disproportionate increase in THC exacerbates the psychoactive properties and increases the possibility of unwanted effects with cannabis use.

On the other hand, cannabis strains such as hemp have been developed that offer low THC levels (less than 1%), freeing cannabis from its main controversial component.

We asked Masha Burelo, PhD in Neurosciences, if cannabis is bad for the brain. Here is his answer:

Is it true that cannabis is bad for the brain?

The answer to this question is not as simple as yes or no, there are different nuances.

Several studies suggest that marijuana high in THC can have negative effects on the brain, such as decreased memory, attention and learning ability, especially if used chronically and from an early age.

Other studies have found that certain components of cannabis, such as CBD or cannabidiol, may have neuroprotective and beneficial properties for certain neurological diseases.

Thus, the answer as to whether cannabis is bad for the brain or not depends on many variables and depends on several factors, especially the type of cannabis, the amount consumed, the frequency of use, the age at which use began, and the dose.

Below is more detailed information on the effects of cannabis on the brain.

The effects of cannabis on the brain: what the research tells us

Cannabis interacts in different ways with the endocannabinoid system. In recent years, it has been observed that the effects of cannabis on the brain can be negative, mostly due to the very high THC concentrations present in cannabis plants today.

The detrimental characteristics of THC’s effects of THC on the brains of of users have been documented through a large body of scientific evidence. These characteristics are linked to the interaction of marijuana THC with the cannabinoid CB1 receptor.

Different types of cannabis and their respective risks

Before delving into the effects of cannabis on the brain, it is important to know that there are different types of cannabis and their properties are different. Marijuana and hemp are both Cannabis sativa plants, but differ in their chemical composition and uses.

Marijuana is a variety of cannabis that contains high levels of THC, the narcotic compound responsible for the “high” effects associated with the consumption of this plant. Marijuana is commonly used as a recreational and medicinal drug, as it can have analgesic, anti-inflammatory, relaxing and psychoactive properties.

Hemp, on the other hand, is a variety of cannabis with no THC (in some cases, less than 0.2%) and high levels of CBD, a non-psychoactive compound that has certain medicinal and therapeutic properties. Hemp is used for a wide variety of industrial purposes, including the production of paper, textiles, food and cosmetics, among others.

In other words, the differences between marijuana and hemp are important in terms of composition. While THC is commonly used as a recreational and medicinal drug, hemp contains low levels of THC and is used for a wide variety of industrial and commercial purposes.

What are the negative effects of marijuana use on the brain?

Chronic marijuana use generates a constant interaction of THC with CB1 receptors, disrupting the natural communication (synapse) adjustment performed by endocannabinoids. Thus, in the long term, THC affects neuronal circuits (1) resulting in memory problems, development of anxiety, depression and even paranoia.

Memory and learning impairment

The consumption of compounds that produce CB1 activation can affect synaptic plasticity (1); this means that the constant activation exerted by THC does not allow neurons to establish new connections with other neurons, affecting processes such as memory and learning (2).

Marijuana can also predispose or produce psychiatric disturbances such as anxiety (3, 4) paranoia (5, 6, 7, 8, 9) and depression (10, 11, 12), which are actually due to the effects of THC. This is because THC can alter the activity of a brain structure called the amygdala, which is involved in the development of fear and anxiety.


Although cannabis does not produce an addictive effect as alcohol or tobacco do. Regular marijuana use builds tolerance to the effects of THC in the brain, leading to increases in cannabis use to produce the desired effect.

Effects of THC on the brains of young people

Before reaching adulthood, the brain presence of CB1 receptors is greater and, therefore, there is more potential for the effects of THC in the brain to affect exponentially (13, 14).

It has already been documented that cannabis use in adolescence leads to alterations in cognitive processes, resulting in poor academic performance (15), decreased IQ (IQ; 16) and memory impairment (17, 18, 19).

On the other hand, the result of its use at an early age can lead to a smaller size of the brain morphology, especially a smaller volume of white matter (14, 20).

Effects of THC on pregnancy and breastfeeding

THC, like many cannabinoids, is lipophilic in nature, so it can be excreted in breast milk (21) and can cross the placental barrier and reach the pregnant baby (22).

One research group reported that children of women who smoked cannabis during pregnancy, although they did not have lower IQ levels, had deficits in visual analysis and lower attention span (23).

The personal factor in the effect of marijuana

The effects of cannabis on the brain are affected by many factors. There is a study that postulates that variations in the THC response in the brain are due to the particular personality of each individual.

This finding was proposed by a group of researchers, who suggest that people who are more vulnerable to stress, and consequently to suffer from depression and anxiety, may have a tendency to exhibit negative behaviors as a result of the effect of THC on the brain (24).

An example of this is psychosis, manifested as delusions or hallucinations, which generally occurs in people prone to psychotic disorders (24) such as people with schizophrenia.

External factors may play a role in the effects on cannabis use. Society’s perception of cannabis use may vary depending on the cultural, legal and social context of each region. In some countries, cannabis use is considered taboo and associated with illegal behavior, while in others it is seen as a normal and accepted practice.

So, is it safe to consume cannabis?

As mentioned above, the negative effects associated with marijuana use are associated with THC, the psychoactive component. To this we must add the fact that, over the last decades, marijuana strains with very high THC levels, never seen before, have been developed.

While at the time of the Beatles, marijuana contained about 4% THC, today’s marijuana strains exceed 30% THC.

The disproportionate increase in THC exacerbates the psychoactive properties and increases the possibility of unwanted effects.

Strategies for minimizing the risks associated with cannabis use

The safe use of cannabis needs to be assessed by the user. Remember that all the negative effects mentioned here are not obvious to the naked eye, as the damage that is documented through research is generally observed in clinical studies.

For example, if marijuana has been consumed since adolescence or adulthood on a regular basis, the brain has probably already adapted to cover the functional difficulties resulting from chronic THC use. That is, the changes in the brain have already been made and probably, although evident with poor memory or inattention, the symptoms tend to be normalized and unnoticed by the THC user.

  • In general, according to the available scientific evidence, it is wise to avoid using cannabis while the brain is still developing. In this way, normal physiology and growth is not altered so that most of the fundamental brain connections can be formed.
  • Do not use cannabis if you are pregnant. Avoid the use of cannabis during pregnancy and breastfeeding, due to its possible undesirable effects on the baby. Cannabis, especially THC – perhaps even in very small doses – can alter the formation of neural connections.
  • Due to the long-term effects and tolerance that marijuana with high THC levels generates, it seems sensible not to consume it habitually. If you decide to consume cannabis, stay hydrated. Cannabis can cause dry mouth and eyes.
  • In adulthood, in case of consuming cannabis, choose wisely the variety, being the most appropriate those without THC.

In conclusion, it is important to make informed decisions and consult a health professional if you have any questions or concerns. Also, take into account the laws and regulations of the country where you live.

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  2. Chen, R., Zhang, J., Fan, N., Teng, Z. Q., Wu, Y., Yang, H., Tang, Y. P., Sun, H., Song, Y., & Chen, C. (2013). Δ9-THC-caused synaptic and memory impairments are mediated through COX-2 signaling. Cell, 155(5), 1154-1165.
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Masha Burelo
Investigadora en cannabinoides | Doctoranda en Neurociencia

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