Why nicotine is as addictive as heroin

SCIENTISTS reckon they have solved a puzzle about nicotine addiction: why, if it gives the brain less of a buzz than drugs like cocaine or heroin, does it generate comparable withdrawal symptoms?

Now, experiments with rats have shown that nicotine, the active drug in tobacco, depresses the brain's ability to experience pleasure and respond to chemical "rewards".

Researchers from the Scripps Research Institute in La Jolla, California, found that rats suddenly deprived of nicotine had to be given much more of a pleasurable reward stimulus to get the same buzz they had before.

Using electrodes implanted in the rats' brains, the researchers measured the levels of "reward" experienced by chemical receptors. Drugs such as cocaine, heroin, alcohol and nicotine all produce their "high" when parts of their molecules latch on to chemical receptors in particular nerves in the brain. Addiction is a reflection of a physical demand by those receptors for more of the chemical. Getting used to the absence of the "high" produced by those molecules is part of the process of withdrawal, and varies in severity for different drugs.

In the experiment, nicotine withdrawal produced a decrease in brain reward function - meaning that for the same stimulation, the nerve centres experienced a smaller buzz. The effects lasted four days, during which the rats showed the classic signs of withdrawal such as anxiety, irritability and craving.

The scientists wrote in the journal Nature: "The decreased function in brain reward systems during nicotine withdrawal is comparable in magnitude and duration to that of other major drugs of abuse and may constitute an important motivational factor that contributes to craving, relapse and continued tobacco consumption in humans."