Younger people more susceptible to nicotine addiction than middle-aged adults

People in their late teens and early 20s may be more sensitive to nicotine and more susceptible to nicotine addiction than middle-aged adults, according to a new study in mice from researchers in the Penn State Department of Biobehavioral Health. The results provide evidence that the effects of drugs on the body - both medication and misused substances - change over the lifespan in ways that clinicians and researchers need to consider when developing and prescribing treatments, the researchers said.

Doctoral student Carlos Novoa and his adviser, Thomas Gould, Jean Phillips Shibley Professor of Biobehavioral Health and head of the department, led the study. The researchers demonstrated that nicotine lowers the body temperature of young-adult mice more quickly and reduces their movement more significantly than middle-aged mice. These results indicate how the effects of nicotine change as people age, according to the research team.

Results of the study were published in Behavioral Pharmacology.

Gould's prior research has illustrated the differential effects of nicotine in children, adolescents and young adults. The current study demonstrated that those effects differ even among those considered adults: young adult mice - aged two months - respond more acutely to a nicotine dose of the same strength relative to their body size than middle aged mice - aged eight months.

Sometimes, people think of development as something that occurs until we reach a certain age - like 18 or 25 - and then stops. But people continue to develop and change across their entire lifespan, and this affects how our bodies respond to medications and other chemicals, including nicotine. This research adds one piece to the puzzle of all the factors - age, biological sex, genetics and many others - needed to create effective medical treatments and policies for all people."

Thomas Gould, Jean Phillips Shibley Professor of Biobehavioral Health

In this study, both young adult and middle-aged study subjects displayed decreased movement after receiving nicotine, but young adults reduced their movements more than middle-aged subjects. This indicates that the young adult subjects experienced the effects of nicotine more intensely, according to the researchers.

"Since we know that young adults are more likely to smoke or vape for the hedonic sensation - as opposed to older nicotine users who are more likely to use because they are addicted or to manage stress - this larger response matters," said Novoa, the first author of the study. "The younger you are, the more acute your response to nicotine. This has implications both for prevention messages and for supporting young nicotine users who want to quit."

Nicotine also had a hypothermic effect on the mice, meaning it reduced their body temperatures. Both young adults and middle-aged subjects experienced similar levels of body temperature reduction, but young adults experienced the temperature drop more quickly.

The physiological manifestations of the pharmacological effects of nicotine - decreased movement and body temperature - demonstrate activation of the cholinergic system, one of the dominant neurotransmission systems in the brain and body, the researchers said. Despite differences between mice and humans, these pharmacological effects provide relevant information about the impact of nicotine on people because of shared biological and genetic substrates, Gould said.

"A human's body temperature may not drop like a mouse's, but the activation of the cholinergic system is consistent across mammals," Gould said. "The differential activation among younger and older research subjects illustrates the point of the study: We should not automatically approach smoking prevention or cessation for young adults and middle-aged adults in the same way."

This study and others like it are needed to design interventions that make quitting more successful, the researchers said. Currently, fewer than 10% of attempts to quit smoking succeed, according to the Centers for Disease Control and Prevention.

"The results demonstrate that young adults are more susceptible to the impact of nicotine," Novoa said. "This puts them at greater risk for developing addiction to the drug, which has implications for both prevention programs and treatments. The legal age to buy tobacco products is 21, but the risk for a 21-year-old individual is higher than it is for a 45-year-old. We need to understand how nicotine affects people based on their individual characteristics so that we can better prevent smoking and help people quit."

Prescilla Garcia-Trevizo, who earned her master's degree in biobehavioral health from Penn State, also contributed to this research.

The National Institute on Drug Abuse, Fulbright Minciencias Colombia Scholarship, the Jean Phillips Shibley Endowment and Penn State supported this research.