A new study from Columbia University highlights the role of tobacco in cocaine addiction. The research indicates that nicotine may be a key "gateway" drug in a biological as well as a social context.
Dr. Amir Levine says there is some support for the gateway hypothesis, that adolescents begin drug use with alcohol and nicotine, then advance to marijuana and more serious drugs.
"And then we were wondering whether that sequence, apart from having cigarettes more available and alcohol more available, whether there was also a biological effect of these drugs on other drugs later on down the line."
To find an answer, Levine and his colleagues used laboratory mice, and added nicotine to their water. Then they injected the mice with cocaine and compared their behaviors with drugged mice that had not gotten the nicotine.
"And what we found was, that when they were treated with nicotine first, the effect - their behavioral effects - were much more pronounced when they were given cocaine."
And Levine says researchers saw that effect even with very small amounts of nicotine.
Co-author and Nobel laureate Dr. Eric Kandel, adds that nicotine dramatically increases the effect of cocaine.
"And it sort of makes a little bit of sense, why people start with nicotine and then go on to cocaine. Because if they're smoking nicotine and they begin with cocaine, they get a wow!"
Nicotine has a direct effect on DNA, Amir Levine explains, essentially exposing genes that are linked to addiction.
"So then, when you give cocaine, certain genes that are involved in addiction are greatly expressed, much more than if you give cocaine by itself."
For real-world confirmation, another co-author, Denise Kandel, - Eric Kandel's wife - reviewed a 1992 study of cocaine users. "And she saw that if you started smoking before you started cocaine, you are much more likely to become addicted to cocaine."
On the other hand, those who used cocaine but hadn't smoked before were less likely to become addicted.
Co-author Eric Kandel says a deeper understanding of the biological process of addiction may lead to more effective treatments.
"The molecular insights that we're getting - and we plan to refine - should allow us to think about new approaches to therapy."
Writing in Science Translational Medicine, the authors also say their research emphasizes the need for more effective anti-smoking programs, especially targeted toward young people.