Marijuana: science reveals its long-term effects on the brain

Marijuana: science reveals its long-term effects on the brain

The use of marijuana is a widespread practice nowadays , being one of the most consumed drugs.

Although socially has been seen as a soft drug comparable to alcohol and with relatively little risk in its use (in fact it has interesting properties that make it very useful at a medical level in different diseases and disorders), the frequent use of this drug can have relevant negative long-term effects, especially with regard to the brain and its structure.

Of course, that does not mean that it is a very dangerous drug comparable, for example, to heroin. However, the defence that has been made about the supposedly innocuous nature of its use is hardly defensible today, as we shall see.

What is marijuana?

Marijuana is one of the many forms in which cannabis is consumed, specifically using chopped and shredded leaves and stems of the plant. This substance has psychoactive properties that are known since ancient times, having been used in a medical and recreational way since then by different peoples. Nowadays its consumption is widely spread all over the world, especially for recreational purposes, and it is even legalized in some places under certain conditions.

It is a substance whose initial effects are slightly stimulating and euphoric, to go on to induce states of physical and mental relaxation. It causes a decrease in the level of tension and pain, increases the sensation of hunger and reduces and slows down motor movement. It is also effective as an antiemetic and anticonvulsant.

The effects of this product are well known when it comes to the short term. However, there is more discussion regarding the long-term effects of marijuana , with often conflicting results depending on the type of study conducted. Despite this, evidence today suggests that regular use of marijuana causes the health of the brain to be eroded more than it should be over time.

Long-term effects of marijuana

While cannabis, especially in its marijuana form, is a widely known substance, studies of its effects have always been surrounded by great controversy. A great deal of research has been conducted, in some cases with unclear results, on the outcomes of its use. However, several studies have shown that its use can cause long-term effects on the brain and behaviour.

It is important to bear in mind that we are talking about cases where consumption is frequent over time. The effects in question depend on the age and the moment of neurodevelopment in which the consumption begins , as well as the time during which the consumption has taken place.

1. Orbitofrontal cortex reduction

One of the results that research has shown is that the continued use of marijuana causes a clear reduction of the grey substance, especially in the orbitofrontal cortex . This also implies a lower long-term capacity for carrying out tasks that depend on this area, such as impulse control or planning.

2. Increases neuronal connectivity

Despite this, many habitual users of this substance show apparently normal behaviour after many years of using marijuana. The reason for this is that, as reflected in other studies, despite the reduction of brain gray matter , the connectivity between the remaining neurons is increased , so that this loss is somewhat compensated for.

That is, although under normal conditions an increase in the connectivity of the neurons would be good news, in this case it is the result of many neurons dying , making those that remain have to “work” more; it is a mechanism of the brain to try to replace the loss of thickness of the cortex. Furthermore, this increase in connections is smaller and smaller as the time of consumption increases.

3. Decreased performance and memory capacity

Different studies reflect that regular cannabis use may eventually lead to a decline in the intellectual capacity of subjects, performing less well and having lower test scores than a non-user. However, many contradictory results have been found in this type of cognitive skills, which means that this phenomenon may not be significant.

What there is solid evidence of is that marijuana use produces long-term problems in various types of memory .For example, these alterations result in greater difficulty in passing on the contents of short-term memory to long-term memory.

It is important to note that these effects are especially noticeable in people who consume throughout their developmental process, i.e. adolescents, due to the structural modification of the brain that cannabis use can entail. In educated adults who start consuming this decrease is less.

4. Does it promote hippocampal neurogenesis?

One of the most widely reported positive effects of cannabis is the ability to promote the formation of new neurons in the hippocampus , the region of the brain involved in the processing of memories. In fact, one of the medicinal applications of cannabis takes advantage of this factor and the fact that it enables the formation of beta-amyloid protein to be reduced in order to help combat certain disorders that cause progressive degeneration of the hippocampus.

However, recently it has been seen that this occurs in laboratory rats used for experiments, but not in humans: in our case, the birth of new hippocampal neurons is practically non-existent in adults.

5. Can produce psychotic outbreaks

While this is not always the case, some variants of cannabis can facilitate the development of psychotic breaks in people who are genetically predisposed to them, especially when they begin to use in adolescence. This is because early use hinders the correct neuronal maturation of the connection between the prefrontal and limbic systems, which facilitates the appearance of hallucinations and makes behavioural control and inhibition difficult. In some cases it can potentiate the expression of schizophrenia.

6. Decreased impulse control

Another of the effects observed and directly linked to the decrease in grey matter in the frontal cortex is the decrease in impulse control . The capacity to inhibit behaviour is linked to specific parts of this lobe, which is responsible for counteracting the power of the limbic system, which is related to emotions and the appearance of desires.

Bibliographic references:

  • Colizzi, M., Iyegbe, C., Powell, J., Blasi, G., Bertolino, A., Murray, R. M. y Di Forti M. (2015). Interaction between DRD2 and AKT1 genetic variations on risk of psychosis in cannabis users: a case-control study. npj Schizophrenia 1, 15025 doi:10.1038/npjschz.2015.25.
  • Dennis, C. V., Suh, L. S., Rodriguez, M. L., Kril, J. J. y Sutherland, G. T. (2016).Neurogénesis de adultos humanos a través de las edades: Un estudio inmunohistoquímico. Neurophatology and Applied Neurobiology, 42(7); pp. 621 – 638.
  • Filbey, F. M.; Aslan, S.; Calhoun,V.D.; Spence, Jeffrey S.; Damaraju, E.; Caprihan, A. & Segall, J. (2014). Efectos a largo plazo del uso de la marihuana en el cerebro. PNAS. vol. 11;47. Centro de BrainHealth. Universidad de Texas.
  • Jiang, W.; Zhang, Y.; Xiao, L.; Van Cleemput, J. M.; Ji, S.P.; Bai, G. & Zhang, X. (2005). J.Clin.Invest. 115 (11); págs. 3104 a 3116.
  • Volkow, N. D., Baler, R. D., Compton, W. M., Weiss, S. R. B. (2014). Adverse Health Effects of Marijuana Use. The New England Journal of Medicine, 370, pp. 2219 – 2227.

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