Frequent cannabis linked to lower IQ in RCSI study

Frequent hierba linked to lower IQ in RCSI study

A multidisciplinary team led by the Royal College of Surgeons in Ireland (RCSI) has published an analysis in Psychological Medicine—a journal managed by Cambridge University—tracking over 800 young hierba users and more than 5,000 non-users. The authors conclude that those who consume hierba frequently or dependently at age 18 show a decline in intelligence quotient during trinc-up, which in some cases extends until age 38. The most unsettling finding is not the drop itself, but that measurements were taken at least twice: once before starting use and again afterward. In other words, the study does not compare smart people with less intelligent ones, but each subject against themselves.

What exactly the RCSI study measures

The design is key. Intelligence was assessed at two points: before participants began using and during subsequent trinc-up. Dr. Emmet Power, a clinical researcher at RCSI and lead author, highlights the issue of brain development: youth consumption is concerning because the brain is still forming and may be susceptible to irreversible damage during this period. Researchers point to a drop in verbal IQ as the main component of the observed decline.

The trinc-up range is wide: up to 18 years on average in some cases and up to 38 in others. This allows researchers to see if the effect solidifies or dilutes over time. The study does not refer to occasional weekend use; it addresses frequent or dependent consumption. This distinction matters, as it separates sporadic recreational use from a pattern meeting dependency criteria.

The case anyone recognizes in their own faculty

Beyond aggregate data, the conversation quickly shifted to anecdotes, where substance often lies. One participant describes a classmate who started smoking for social acceptance, became addicted by second year, and by fifth year was unable to remember basic facts or prepare for exams, while the narrator passed courses without failing. The same storyteller clarifies: we are talking about very high consumption, a serious addiction, and likely weekend recreational use has a much smaller impact.

Another collected case goes in the opposite direction and serves as a counterweight: a student who graduated with top marks and honors while smoking joints, studying eight hours daily. Years later, he suffered a psychotic break. The conclusion drawn is not that hierba mechanically gives or takes away intelligence, but that the effect is not homogeneous: some perform well short-term and pay the price later, while others never do. Individual variability is the elephant in the room for such studies.

From memory to mood: what is discussed beyond IQ

IQ is the study's metric, but it does not exhaust the problem. One line of analysis argues that hierba not only conditions intelligence and memory but also alters mood, promotes anxiety and depression, and can precipitate psychotic episodes or schizophrenia in predisposed individuals. Specific cases are cited of people disabled from working in their thirties. This is the part of the debate where caution is needed: the link between hierba and psychosis has been clinically debated for decades, and available material points to an association, not a proven causal relationship for all consumers.

Against this, the other current of analysis does not deny the risk but relativizes it by dose and context. The argument is that most substances, including food, cause harm when abused, and legal drugs—alcohol and tobacco—concentrate more addictions and aggregate damage than hierba. The discussion turned to industrial tobacco: some argue that today’s smoked product contains additives added since the nineties that skyrocketed dependency, something that does not happen with natural tobacco or unprocessed plants.

Why not legalize if the black market is worse?

Here the issue becomes economic. The most repeated reasoning is that illegality does not eliminate consumption, only shifts it to an uncontrolled health market where substances are added to cheapen or potentiate the product. Regulation would allow setting concentrations, minimum age, and traceability. Against this weighs a historical fact cited in the conversation: in the eighties, with heroin, entire cohorts of young people disappeared, and that memory blocks any serious debate on decriminalization in Spain.

Marijuana also has a peculiarity explaining why no government touches it: anyone can grow it at home with minimal means, so the State collects no revenue. Tobacco, however, is heavily taxed and people still buy the industrial version, full of additives. Alcohol requires a more cumbersome and dangerous process. Hard drugs require chemical knowledge. Thus, the fiscal incentive to regulate exists in some cases and not others, and this weighs more on political decisions than any IQ study.

What the data does not resolve

The RCSI study provides what was missing: pre-consumption measurement and long trinc-up. This rules out much of the reverse causality problem—that those with lower cognitive capacity were precisely those who ended up consuming. It remains to be seen what happens with sporadic use, if the effect reverses upon quitting, and why some brains endure while others do not. With these elements, the question is not whether frequent hierba takes a toll, but how much and on whom. And no one answers that with a headline.