Marijuana is generally considered not to be an addictive drug in the traditional sense—even heavy marijuana users who stop smoking rarely experience withdrawal symptoms. However, a new study suggests that marijuana smokers can still experience difficulties quitting. Researchers at the University of Mexico and University of Colorado used functional magnetic resonance imaging (fMRI) to see that even marijuana users who had not smoked for three days still respond with cravings for marijuana when presented with visual or auditory cues.

The study's participants were 38 regular marijuana users who had abstained from lighting up for 72 hours. The researchers used fMRI to observe if and when cravings were stimulated by auditory and visual cues. When the abstaining marijuana smokers had scripts read to them that evoked imagery of marijuana smoking, were presented with smoking paraphernalia, or both, areas of their brains were activated that suggested they were craving a toke.

Their desire to smoke varied directly with the amount of marijuana-related content—the more the speakers in the script spoke of marijuana, the more the listeners craved it.

The areas of the brain that had the most blood oxygen level dependent signals were the dorsal anterior singular cortex, which processes reward-based cognition, and the amygdala, indicating that emotional processing was also taking place. The researchers found these responses to be similar to those seen when alcohol and drug users or gamblers are presented with the corresponding stimuli.

The study also found that the exact form of stimulus was less important than its general relation to the drug. So, for example, when users were shown a pipe, even the participants who did not use one would still show indications of a craving in the appropriate areas of the brain. Combining visual and auditory cues or, as previously mentioned, increasing the number of references to marijuana, made the cravings stronger.

The results of this study suggest in a broad way that certain kinds of therapy may not actually be so effective for marijuana users. For example, a heavy marijuana user attempting to quit may join a support group or enroll in a treatment center in which he does nothing but talk about marijuana, which may serve to significantly ramp up his cravings. However, another study cited in the report found that users that have been abstinent for a while no longer respond to these cues.

Neither study looked at the effects of negative stimuli, such as seeing a joint pulled out of the pocket of a dealer being searched by a police officer. Nonetheless, the existence of these neural responses suggest that a user who cannot remove himself from a stimulus-ridden environment may find it very hard to quit in the short term.