Cannabis use may increase the likelihood of becoming addicted to nicotine, suggests a study in rats funded by the National Institute on Drug Abuse.
Data from previous epidemiologic studies have suggested that people who smoke marijuana are more likely to become addicted to cigarettes, but the reason why was unclear.
To probe whether biological factors may be involved, the researchers injected rats with tetrahydrocannabinol (THC), the main psychoactive component of cannabis, for 3 days (Panlilio LV et al. Neuropsychopharmacology. doi: 10.1038/npp.2013.16 [published online January 10, 2013]). A week later the investigators implanted catheters in the animals to give them an intravenous dose of nicotine or a placebo when they completed a task. Of rats in the nicotine group, 94% learned to complete the task to get their dose, compared with 65% of the placebo group. When the rats had to work harder to obtain the dose, those in the nicotine group were more likely to persist.