The question of the long-term effects of cannabis – including potential addiction – has become more important than ever as various jurisdictions move forward with the legalisation of medical and recreational cannabis. Although solid evidence remains scarce, a new study assessing cannabis-seeking behaviour in rats may offer some insight.

The study, carried out by researchers at Washington State University’s (WSU) Integrative Physiology and Neuroscience, claims to demonstrate that cannabis causes addiction. They discovered that rats, given the ability to self-administer cannabis vapour, consistently did so.

The Study

Animal studies involving cannabis are not often considered to be hugely representative of in comparison to the effects on humans. However, the researchers stress that rats involved in the study responded to cannabis vapour in much the same way as humans.

Ryan J. McLaughlin, a professor in WSU’s Integrative Physiology and Neuroscience unit, and the study’s senior author said:

“It’s always difficult to establish reliable cannabis-seeking behavior using animal models. In this study, we have a clear and reliable response for cannabis by utilizing the very first self-administration model involving on-demand delivery of whole-plant cannabis vapor.”

In the study, rats were sorted into three groups and given access to a nose-poke system that would release one of three formulations. Either THC-rich cannabis vapour, CBD-rich cannabis vapour, or a puff of air would be given to the rats. The rats were then observed over a number of days.

By the end of the study, it was discovered that the group receiving high-THC cannabis were seeking out the vapour more often than rats in the two other groups. The researchers note that on some days, these rats were doing so more than twice as often.

After three weeks, the researchers removed the cannabis vapour from the delivery systems. Interestingly, it was observed that the rats would administer far more nose-pokes than they had previously. The researchers believe that this shows cannabis-seeking behaviour.

“It went from 17–18 nose pokes up to 70–80 on average. They were trying to figure out why it wasn’t working.”

Although this study provides an interesting insight into the possible drug-seeking effect of cannabis, it represents an early stage of research when considering its relation to human behaviour. However, previous research has led to the expectation that 1 in 10 cannabis users will become addicted to the drug.

Despite this, cannabis has often been considered as an effective harm reduction strategy in addiction to other, more harmful drugs.