Cannabis is the most popularly used proscribed drug in our society, particularly so amongst young people, including young pregnant women. Yet we still know very little about the consequences of smoking hash and marijuana for the immature brain.

Several epidemiological studies support the gateway hypothesis, which states that cannabis smoking at a young age is a gateway to other kinds of drug abuse later in life. However, it has not been ascertained whether it is cannabis per se that increases the risk of other drug abuse or whether common underlying social or hereditary risk factors make cannabis users more prone to it.

“We wanted to empirically test the gateway hypothesis in the absence of social and moral factors,” says scientist Maria Ellgren at the Department of Clinical Neuroscience. “All addictive drugs affect the brain’s reward system, and our question was therefore whether cannabis exposure causes molecular and neurochemical changes that give a greater reward effect from other narcotics.”

The study was conducted on rats at an age corresponding to the teenage years in humans. The animals were given either cannabis or cooking salt at regular intervals for their entire adolescence. When the rats had reached adulthood, those that had been given cannabis showed changes in the brain centres that are strongly associated with feelings of reward and well-being. They also had a higher intake of heroin when given free access to the drug in experiments where they could determine themselves the amount of drug received. Such changes were not noted, however, in the control population of salt-fed rats.

“We did similar studies at the foetal stage, with similar results to those we obtained with adolescent rats,” says Ms Ellgren. “However, we also found that early use of cannabis had no observable effect on sensitivity to a CNS-stimulating drug like amphetamine, which is also interesting.”

Thesis: “Neurobiological effects of early life cannabis exposure in relation to the gateway hypothesis” by Maria Ellgren at the Department of Clinical Neuroscience, Karolinska Institutet. The public defence will take place on February 9, 2007.

For further information, please contact:

Maria Ellgren
Phone: +46-8-5177 24 79
Mobile: +46-70-680 06 28

Press Officer Katarina Sternudd
Phone: +46-8-524 838 94