The researchers found that non-smokers who used cannabis were more likely to start smoking, while those who already smoked tobacco were more likely to continue.

Former smokers who use cannabis also had a higher chance of picking up the habit again.

The increased odds were also found even in those that didn’t have a cannabis use disorder, which is when the drug impairs in functioning or users have difficulty quitting or cutting down on use.

The researchers added that as cannabis use is much more common than cannabis use disorder, the impact of the drug on cigarette use could be greater than previous estimates have suggested, which were based on studies of cannabis use disorder alone.

“Developing a better understanding of the relationship between marijuana use and cigarette use transitions is critical and timely as cigarette smoking remains the leading preventable cause of premature death and disease, and use of cannabis is on the rise in the US,” said senior author Renee Goodwin.

Although cigarette smoking is declining, marijuana use is increasing. Previous research by Goodwin and colleagues also showed that the number of smokers who use cannabis has also risen sharply in the last two decades, with smokers more than 5 times as likely as nonsmokers to use marijuana daily.

Goodwin also added that understanding the links between cannabis use and starting to also smoke cigarettes is particularly important among younger users, with recent research suggesting that cannabis use is more common among adolescents than cigarette use.

The results can be found published online in the Journal of Clinical Psychiatry.