Smoking cannabis does not worsen the cognitive decline experienced with aging. Indeed, perhaps it could have a protective effect. This is what emerges from a study recently published in the journal Brain and Behaviour, which analyzed the changes in the results of an intelligence test to which over 5 thousand Danish men underwent twice after several decades, relating them to the use, or not, of the substance during this time period.
The work was carried out by researchers at the University of Copenhagen using data from the mandatory tests that all Danish men between the ages of 18 and 26 must undergo by law, as part of the country’s compulsory military service. The researchers managed to recontact over five thousand citizens who had taken the test at least three decades earlier, and who agreed to undergo the same assessment again at an average age of 64 years.
After taking the test, the volunteers were asked if they had ever used cannabis. About 40 percent gave a positive response, 10 percent said they had used the substance frequently (at least two joints a week) for a period of less than 10 years, and another 12 percent said they had used cannabis frequently for over a decade. However, 92 percent of cannabis smokers also said they had stopped using the substance for at least a year at the time of participating in the study.
By comparing the results of the intelligence test carried out in youth with those obtained at the age of 70, the researchers were therefore able to evaluate the impact of cannabis consumption on the decline in cognitive abilities that occurs physiologically with ageing. And according to the results, the substance does not seem to contribute negatively to this physiological decline, on the contrary: on average smokers showed a worsening of the test results by 1.3 points.
The differences are too small to claim that they have any clinical validity, but they are present nonetheless. And this makes the authors of the study say that they could at least demonstrate that the substance does not damage cognitive abilities, even in the case of prolonged use. In the past, other research has given results in line with those of the Danish study, revealing for example that THC (the active ingredient of cannabis) seems to protect the brain functions of elderly mice, or that it can reduce the risk of suffering from neurodegenerative diseases, such as Alzheimer’s.
However, there is also research going in the opposite direction, and therefore it is too early to be able to give a definitive answer on the topic. Also because in the Danish study it was not possible to verify how many and which of the participants were using the substance when they underwent the test for the first time. And this leaves open the possibility that the differences that emerged at the time of the second test did not derive from a protective effect, but rather (on the contrary) from the fact that for cannabis smokers the results obtained in youth were negatively influenced by having consumed the substance , while during the study 92 percent of them had stopped for more than a year.
Even if it were, the new study would confirm, if nothing else, that any negative effects of cannabis consumption are completely reversible even after smoking it regularly for decades. “Several research suggests that the negative effects of cannabis on cognitive functions may disappear after prolonged abstinence,” the authors write in the conclusions of the study. “The negative effects are no longer evident after three months of sustained abstinence, even in heavy users, and this indicates that in most cases the use of cannabis does not produce irreversible damage.”