Marijuana use is four times as likely among American young adults who are already tobacco smokers than those who are non-smokers, according to a recent Facebook-based survey conducted by researchers at the University of California, San Francisco (UCSF).

The survey findings show a much greater prevalence of marijuana and tobacco co-use among smokers age 18 to 25 than previously reported, said the research team. Past studies have shown that roughly 35 percent of young adult tobacco users also used marijuana within the past 30 days.

"We were curious whether rates would be different in our study where we reached out through social media and the Web," said Danielle Ramo, PhD, a post-doctoral scholar in the UCSF Department of Psychiatry, and lead author of the study. "And rates were much higher, which shows the problem might be larger than we realize."

The research, published in BioMed Central's open-access journal Addiction Science and Clinical Practice, provides a detailed analysis of the survey results, which shows that smoking cessation campaigns need to factor in cannabis in treatment plans.

The survey recruited participants online, which is a much different approach than traditional surveys that rely on in-person or over-the-phone interviews. The researchers primarily used Facebook by placing a series of paid ads, but also used Craigslist and a survey sampling firm.

The research team said Internet surveying can have more benefits over traditional surveys, as young adults may be more inclined to answer honestly via anonymous online sampling.

The first phase of the two-part study was used to identify only tobacco smoking patterns. The second phase asked participants to answer a tobacco/marijuana use survey, which utilized data encryption to ensure anonymity and prevent multiple entries.

Of the 3,500 individuals who completed the marijuana and tobacco co-use survey, the team found usage was highest among white people, people from the Northeast, people in rural areas and those who were non-students. Of the 68 percent who said they were daily smokers, 53 percent also said they had used marijuana in the last month.

Judith Prochaska, PhD, MPH, associate professor of psychiatry at UCSF and senior author of the study, said: "Residence in a medical marijuana state was unrelated to the prevalence of marijuana use as well as the co-use of marijuana and tobacco in this young adult sample." She added that prevalence of marijuana use also "did not differ by respondents' age, income or gender."

"Adapting the social media aspect into intervention and incorporating the social environment are new ways to approach finding the most effective means for treatment," said Prochaska.

The team plans to continue use of social media surveys to see what treatment plans work best, in which participants will be able to not only contact clinicians for support, but to also contact other smokers within the online community. Motivational Facebook messages and formal moderated groups online also will be integrated into treatment.

"This format allows them to remain anonymous as much as they want, but have ease to access interventions when they are at the age when they are less likely to enter a treatment center, research lab or clinic," said Ramo.

The study was supported by an institutional training grant, a center grant from the National Institute on Drug Abuse and an individual Postdoctoral Fellowship Award from the California Tobacco-Related Diseases Research Program.