Teens used to try alcohol first, then tobacco, and then marijuana. Now, marijuana is increasingly the first “gateway” substance for adolescents, according to new research.

This trend is not because teens are smoking cannabis more than ever. Rather, the change is because teens are smoking cigarettes and drinking less while the numbers for marijuana have held steady, according to Katherine M. Keyes, a professor of epidemiology at Columbia University and co-author of the new study, published this week in the journal Drug and Alcohol Dependence.

“As we’ve seen the dramatic declines in alcohol and tobacco, we haven’t seen dramatic declines in marijuana, so now every year it’s more and more likely that kids are starting their drug-use careers with marijuana,” says Keyes. She adds that rates of teen drinking and smoking started to fall — thanks largely to widespread public health campaigns — long before the recent wave of pro-marijuana lobbying.

Gateway sequences are malleable

The authors found this by analyzing 40 years of surveys from American high school seniors. For example, in 1995, three-fourths of seniors who used both marijuana and cigarettes had tried cigarettes first. By 2016, only 40 percent had tried cigarettes first. Today, less than half of teens try alcohol and cigarettes before trying cannabis. (The researchers didn’t look specifically at whether alcohol or tobacco came next.) Other studies have found that, in general, teens are doing fewer drugs than ever, except for marijuana.

Most likely, this trend will continue as marijuana becomes less stigmatized and more and more states vote to legalize the drug. Though teens aren’t supposed to smoke marijuana even in the states that have fully legalized it, “it’s not going out on a huge limb to suggest that marijuana is going to be more available at a lower cost to adolescents,” says Keyes. “If you make a substance more available at a lower cost and easier to access, you’re gonna see increases.” After all, it’s also illegal for kids to drink or smoke, but many easily find both alcohol and cigarettes in their own homes.

One important caveat is that the tobacco information only refers to traditional combustible cigarettes and doesn’t take into account the spike in underage vaping (though vaping alone doesn’t account for the lower levels of smoking). “If anything, what this paper shows is that gateway sequences are malleable and very context-specific,” says Keyes. “When you think about substance use in adolescents, you kind of have to keep your eye on the whole picture and not do it substance by substance. The next product that comes onto the scene and delivers nicotine in a way young people like could create a different sequence.”