Scientists in Australia used magnetic resonance imaging (MRI) equipment to test 15 volunteers who admitted to smoking more than five 'joints' a day for over 10 years.

The results were compared to 16 individuals who did not use the drug.

The researchers found that, on average, the smoker's hippocampus – which is thought to govern emotion and memory – was 12 per cent smaller.

They also discovered that the amygdala, which has a part in controlling fear and aggression, was seven per cent smaller in the drug-takers.

The users also performed worse in verbal memory tests and were more likely to have symptoms of schizophrenia and mania.

Neuropsychologist Dr Murat Yucel, of the University of Melbourne, led the research assisted by staff from the University of Wollongong.

His report noted: "Although modest use may not lead to significant neurotoxic effects, these results suggest that heavy daily use might indeed be toxic to human brain tissue."

In May, scientists at New York University tested the brains of a group of 17- to 30-year-old cannabis smokers who used the drug twice a week for a year.

They found no difference between the users' brains and those of non-users.

In 2004, Professor Cyril D'Souza, of Yale University, said the active ingredient of cannabis, abbreviated to THC, caused schizophrenia-like symptoms in users, which ranged from suspiciousness and delusions to poor attention span and memory.

Erik Spandmand

Jeg har svært ved at forholde mig til resultaterne:

Forsøg 1.
Hippocampus: emotion and memory – was 12 per cent smaller.
Amygdala: controlling fear and aggression, was seven per cent smaller in the drug-takers.

Forsøg 2.
They found no difference between the users' brains and those of non-users.

Det kan sku ikke passe at forskere ikke kan komme til enighed her. At 2 individuelle studier, skulle have så stor en difference i folks hjerneskade er sku uacceptabelt og lægger ihøjeste grad op til, er der er en fordrejning af sandheden.

Hvad siger biologerne til det?

Regional brain abnormalities associated with long-term heavy cannabis use.Yücel M, Solowij N, Respondek C, Whittle S, Fornito A, Pantelis C, Lubman DI.
MAPS, ORYGEN Research Centre, 35 Poplar Rd, Melbourne, Victoria, Australia. murat@unimelb.edu.au

CONTEXT: Cannabis is the most widely used illicit drug in the developed world. Despite this, there is a paucity of research examining its long-term effect on the human brain. OBJECTIVE: To determine whether long-term heavy cannabis use is associated with gross anatomical abnormalities in 2 cannabinoid receptor-rich regions of the brain, the hippocampus and the amygdala. DESIGN: Cross-sectional design using high-resolution (3-T) structural magnetic resonance imaging. SETTING: Participants were recruited from the general community and underwent imaging at a hospital research facility. PARTICIPANTS: Fifteen carefully selected long-term (>10 years) and heavy (>5 joints daily) cannabis-using men (mean age, 39.8 years; mean duration of regular use, 19.7 years) with no history of polydrug abuse or neurologic/mental disorder and 16 matched nonusing control subjects (mean age, 36.4 years). MAIN OUTCOME MEASURES: Volumetric measures of the hippocampus and the amygdala combined with measures of cannabis use. Subthreshold psychotic symptoms and verbal learning ability were also measured. RESULTS: Cannabis users had bilaterally reduced hippocampal and amygdala volumes (P = .001), with a relatively (and significantly [P = .02]) greater magnitude of reduction in the former (12.0% vs 7.1%). Left hemisphere hippocampal volume was inversely associated with cumulative exposure to cannabis during the previous 10 years (P = .01) and subthreshold positive psychotic symptoms (P < .001). Positive symptom scores were also associated with cumulative exposure to cannabis (P = .048). Although cannabis users performed significantly worse than controls on verbal learning (P < .001), this did not correlate with regional brain volumes in either group. CONCLUSIONS: These results provide new evidence of exposure-related structural abnormalities in the hippocampus and amygdala in long-term heavy cannabis users and corroborate similar findings in the animal literature. These findings indicate that heavy daily cannabis use across protracted periods exerts harmful effects on brain tissue and mental health.

Scientists in Australia used magnetic resonance imaging (MRI) equipment to test 15 volunteers who admitted to smoking more than five 'joints' a day for over 10 years.

They also discovered that the amygdala, which has a part in controlling fear and aggression, was seven per cent smaller in the drug-takers.

The users also performed worse in verbal memory tests and were more likely to have symptoms of schizophrenia and mania.

Relativt lille antal personer, de har testet. Gad nok vide om deres resultater var statistisk signifikante og med hvilken styrke og hvilken spredning. Når man har så små samples kan det være svært at udelukke tilfældighed.