What do you go through almost every day

Does weed make you stupid?

LAUSANNE The American CARDIA # study is apparently well suited to scientifically substantiate clich├ęs. While researchers recently found in an evaluation that young adults who hang around a lot in front of the telly are no longer the brightest a quarter of a century later, the old junkie wisdom has now been confirmed: smoking weed makes you stupid in the long run.

However, this statement only applies with certain restrictions.

Basically, it is not new that heavy stoners are mentally not on their toes. The current analysis of the CARDIA data is more about whether the consumption of marijuana leads to permanent damage to the brain, i.e. whether people who have smoked a lot of pot at some point in their life will be noticed years later with mental deficits - even then, if they have become abstinent in the meantime.

This question can be answered with a yes and no using CARDIA: When it comes to verbal memory, high cannabis consumption seems to leave traces in the long term, while other cognitive functions are hardly influenced - at least the influence cannot be clearly worked out.

Deficits at high dose

Over 5000 young adults between the ages of 18 and 30 took part in CARDIA. The study began in 1985, so data are now more than 25 years old, and the participants are now around 50 years of age at which they will develop their first cardiovascular disease.

The main aim of the study is to examine the influence of lifestyle at a young age on such diseases. One then wants to derive better prevention approaches from this.

In the interviews, which are carried out every few years, the participants also stated their cannabis use. In questionnaires, they should say how many days they had a joint in the past month.

Researcher around Dr. Reto Auer from the University of Lausanne then extrapolated the information to the other months and calculated the cumulative cannabis dose over a quarter of a century.

The participants were roughly divided into those without any cannabis use - that was only 16% -, those with low consumption (on less than 180 days), with moderate use (0.5-2 years), high consumption (2-5 years) and very high consumption (over 5 years). The latter had smoked weed on at least 1,800 days in 25 years.

The examination after 25 years tested processing speed, executive functions and verbal memory using three different methods (DSST, Stroop test, RAVLT) *. The stoners did worse in all three tests, the more bags they had dragged themselves into in their previous lives, even if they meanwhile stopped using cannabis.

Such a dose effect was only observed with high and very high consumption, not with a cumulative dose of less than two years. So according to these data, you can smoke weed two to three times a month without experiencing long-term cognitive problems - perhaps good news for some.

Accelerated cognitive decline?

But many stoners have a number of risk factors that are already associated with poor cognitive performance: They do less sport, are more often depressed, alcoholic, addicted to nicotine and other illegal drugs.

If such factors were taken into account, the relationship between smoking weed and poor cognition weakened significantly - it only remained significant for verbal memory, and here too the effect size was two-thirds smaller than without such adjustments.

If stoners are stupid, it is largely due to adverse other lifestyle factors and only a small part to marijuana. Nonetheless, a certain effect can be traced back to the drug: If you have a ten-year dose - that is, you smoke 3,650 joints in 25 years - you have to expect that you will be able to remember one out of 15 less words in the RAVLT than absolute abstainers.

You can well imagine that most stoners don't care.

However, one should not draw the reverse conclusion that long-term cannabis use is largely harmless for the brain. In a New Zealand long-term study over 38 years, an accelerated cognitive decline was observed with almost daily consumption.

However, such degradation could not be detected in occasional weed smokers. Unfortunately, the authors of the study around Auer did not provide any information on the cognitive course over the 25 CARDIA years.

This could have been used to tell whether there is also an accelerated decline in the case of intensive consumption. It would also be interesting to see whether high consumption as adolescents and young adults is more harmful than in later life, when brain development is complete. There is much evidence that young people's brains are particularly sensitive to cannabis. However, the study authors do not comment on this.