UNIDENTIFIED MAN: A new victim is being lured into the trap of addiction. High - high, as a kite - the marijuana has done its job well. She can be led now, ready to go along. Casually, he introduces the idea of something stronger, real kicks.
ARUN RATH, HOST:
The idea that marijuana is dangerous because it's a stepping stone to harder drugs, like cocaine or heroin, is pretty old. And it's always been controversial. Dr. Denise Kandel is a professor of sociomedical sciences at Columbia University, and she's been studying drug use and addiction for decades. In the early 1970s, the National Institute on Drug Abuse gave Dr. Kandel money to study marijuana as a possible gateway drug.
DENISE KANDEL: And in those days, you know, you were funded to do marijuana and you were not even supposed to ask about anything else.
RATH: But Dr. Kandel thought it made sense to look at other factors aside from marijuana. Even though she wasn't supposed to, Dr. Kandel went ahead and asked about tobacco and alcohol use. Her instinct paid off.
KANDEL: When I did the analysis, I found that there was a certain sequence that young people seem to be following when they got involved in drugs. They did not start with marijuana, but they started with drugs that are legal for adults in the society, such as beer and wine and cigarettes, other forms of alcohol.
RATH: And tobacco - nicotine - appeared to be the most effective gateway of all. To reinforce her behavioral findings, Dr. Kandel wanted to conduct a biological study. And since you can't really confine kids to a lab and dose them with alcohol or tobacco - or heroin for that matter - science turns to rodents.
KANDEL: When you have an animal model, you can change the order of presentation. You can present an animal with, you know, drug A, see how he reacts to drug B and do the reverse - B versus A.
RATH: Now, Dr. Kandel is not a neurologist. But conveniently, she happens to be married to one and not just any - Nobel Prize-winner Dr. Eric Kandel. Nearly 40 years after Dr. Denise Kandel's paper on the gateway hypothesis was published, she and her husband published a molecular basis for nicotine as a gateway drug in the New England Journal of Medicine.
KANDEL: What we found is that when an animal was primed by nicotine and then was exposed to cocaine, the effect of cocaine was amplified many times.
RATH: Dr. Kandel wants people to pay attention to their results. She says that given how well nicotine primes the brain for addiction, she's concerned about reports showing e-cigarette use among young people on the rise.
KANDEL: Because as we said, you know, nicotine is nicotine, whether it comes from an e-cigarette or from a combustible cigarette, you end up with nicotine in the brain.
RATH: Dr. Denise Kandel. Her original findings on nicotine as a gateway drug came out 40 years ago this year. Her follow-up with her husband was published last fall. Transcript provided by NPR, Copyright NPR.