The Science of Nicotine Addiction
First published 2007. To view the latest Heads Up content, click here.
The news made headlines in 2006: Smokers today get more nicotine from inhaling cigarette smoke than they did in 1998. The news is alarming because nicotine is the chemical in cigarette smoke that causes addiction to tobacco. The Massachusetts Department of Public Health (DPH) reported its discovery that the nicotine yield in cigarettes—meaning the amount of nicotine a smoker gets from a cigarette—had increased steadily between 1998 and 2004. The DPH used information provided by tobacco companies themselves. (Massachusetts is one of only three states in the country to require tobacco companies to report this information each year.)
One deadly consequence of more nicotine yield in cigarettes is that the average smoker will find it harder to quit. Not only is there more nicotine in cigarettes, but nicotine itself is a powerfully addictive drug. In the words of a NIDA-funded researcher, Dr. Daniel McGehee: “It would be difficult to design a better drug [than nicotine] to promote addiction.”
Why Nicotine Is So Addictive
In investigating the addictive power of nicotine, NIDA-funded researchers at the University of Chicago found that nicotine’s effect on the brain is doubly dangerous. It directly stimulates the feelings of pleasure and indirectly keeps those pleasurable feelings going strong.
Pleasure and desire drive the process of addiction. Nicotine, like other addictive drugs, attaches to the core neurons (impulse-conducting cells) of the brain’s reward system. These neurons flood the brain with a neurotransmitter (a chemical messenger) called dopamine. Dopamine is the source of both feelings of pleasure and the desire to repeat behaviors that led to pleasure—in this case, smoking. But nicotine directly stimulates dopamine-producing neurons for only a few minutes at most.
To explain why dopamine levels remain high after direct nicotine stimulus ends, researchers looked at two other neurotransmitters in the brain, glutamate and GABA. Glutamate is a neurotransmitter that speeds up the activity of neurons. GABA is a neurotransmitter that slows down neuron activity.
The researchers discovered that nicotine’s effects on glutamate and GABA cause the pleasurable effects of nicotine to last longer. Nicotine causes glutamate to speed up dopamine release. Nicotine prevents GABA from slowing down dopamine release. The result is a high level of dopamine that lasts more than an hour.
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Massachusetts Department of Public Health, “Changes in Nicotine Yield: 1998-2004,” Massachusetts Tobacco Control Program. Accessed at www.mass.gov/Eeohhs2/docs/dph/tobacco_control/nicotine_yields_1998_2004_factsheet.pdf.
Zickler, “Nicotine’s Multiple Effects on the Brain’s Reward System Drive Addiction,” NIDA Notes, Vol. 17, No. 6 (March 2003). Accessed at http://archives.drugabuse.gov/NIDA_notes/NNVol17N6/Nicotine.html.