Nicotine also attaches to neurons (brain cells) that release a neurotransmitter called dopamine.
Nicotine stimulates neurons to release unusually large amounts of dopamine. Dopamine stimulates the brain's pleasure and reward circuit, a group of brain structures called the limbic system involved in appetite, learning memory, and feelings of pleasure.28
In 40 minutes, half the effects of nicotine are gone.
So smokers get the urge to light up for another dose of the drug. After repeated doses of nicotine, the brain changes. To adjust to too much dopamine, the brain cuts production of the neurotransmitter and reduces the number of some receptors. Now, the smoker needs nicotine just to create normal levels of dopamine in his or her brain. Without nicotine, the smoker feels irritable and depressed. The smoker has trained the limbic system to crave tobacco. Think about how you long for a cold drink on a hot day. Or how you want a sandwich when you are hungry. Craving for tobacco is much28 stronger.
