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People who smoke marijuana are more likely to develop nicotine addiction, a new study reveals.

A new study by the National Institute on Drug Abuse (NIDA) found that exposure to the primary psychoactive chemical compound in marijuana, THC, triggers stronger nicotine addiction in laboratory rats.

The findings published Feb. 6 in the journal Neuropsychopharmacology suggest that individuals whose "gateway drug" was marijuana may have a greater risk for nicotine addiction when they try cigarettes later on.

In the study, researchers exposed rats to THC or a placebo for three days.  Afterwards, they tried to train the rats to self-administer nicotine intravenously by pocking their noses through a hole in the cage.

Not all of the rats in the study learned how to do this.  However, researchers assumed that rats that successfully learned how to self-administer nicotine were more motivated to get a fix and were therefore more "addicted".

Researchers found that previous THC exposure increased the laboratory rats' likelihood of learning how to self-administer nicotine.

While only 65 percent of rats who'd been exposed to the placebo learned how to successfully self-administer nicotine, an overwhelming 94 percent of rats previously exposed to THC acquired the nicotine self-administration response.

Furthermore, when researchers manipulated the price of nicotine by increasing the response requirement, THC-exposed rats still maintained higher levels of intake than control rats, suggesting that THC exposure increased the value of nicotine reward, according to researchers.

"Although it is more common for drug abuse to progress from tobacco to cannabis, in many cases cannabis use develops before tobacco use," researchers wrote in the study. "Epidemiological evidence indicates that prior cannabis use increases the likelihood of becoming dependent on tobacco."

However, it should be noted that because the study was conducted on rats, the findings might not actually translate to humans.  

Researchers noted that previous studies on THC-exposure found that it did not increase animals' risk of acquiring an addiction to heroin or cocaine.  In light of the recent findings, Researchers suspect that the brain systems responsible for feelings of reward in nicotine and marijuana users interact in some way.

"These results contrast sharply with our earlier findings that prior THC exposure did not increase the likelihood of rats acquiring either heroin or cocaine self-administration, nor did it increase the reward value of these drugs," researchers wrote.

"The findings obtained here suggest that a history of cannabis exposure might have lasting effects that increase the risk of becoming addicted to nicotine," they concluded.