Nicotine: From plants to people

Facts about nicotine

Nicotine is addictive and not risk free, but the harmful effects associated with the use of cigarettes and other combustible tobacco products are primarily attributed to the smoke produced during the burning of tobacco and not nicotine itself. Cigarette smoke contains thousands of chemical compounds, approximately 100 of which are categorized as harmful and potentially harmful constituents (HPHCs) by public health authorities.

Quitting tobacco and nicotine altogether is the best way to reduce the risk of smoking-related diseases, like lung cancer, cardiovascular diseases, and emphysema. Cigarette smoke also stains the teeth and causes bad breath.

Nicotine can be absorbed into the body in various ways: through the lungs (e.g., cigarettes, heat-not-burn, or e-cigarettes), the mouth (e.g., Swedish snus or nicotine pouches), or the skin (e.g., nicotine patches). The route of uptake affects the rate and amount of nicotine taken up into the body. Once absorbed, nicotine enters the bloodstream and binds to receptors in the human nervous system, including the brain, triggering an array of reversible physiological responses (e.g., a transient increased heart rate and blood pressure). 

It takes time after starting to use a nicotine-containing product for nicotine to reach the brain in sufficient concentration to cause an effect. That time ranges from approximately 10 seconds, as with smoking, to up to an hour with the nicotine patch. Nicotine is also constantly being cleared from the body. It’s metabolized mainly by the liver and the metabolites are excreted via the kidneys. 

 

Where does nicotine come from? 

The simple answer to this question is: plants. More specifically, plants in the Solanaceae family, commonly known as nightshade. This family includes tomatoes (~332 ng of nicotine each on average), potatoes (~675 ng), and eggplants/aubergines (~525 ng). Because nicotine is present in many common food plants, it is in our diet in small doses. Research estimates that people eat about 1,400 ng of nicotine every day in ordinary food. To put that into perspective, a single cigarette contains ~12 mg of nicotine—around 18,000 times more nicotine than a potato, by mass. But only a fraction (<2 mg) of that nicotine is transferred into the smoke of a cigarette. 

Nicotine is created in the plant’s roots when two chemical compounds—pyridine and pyrrolidine—are joined together before being transported to the leaves. The genes behind this combination exist in many plants, but genetic duplications in the nightshade family are believed to have led to higher nicotine production in tobacco plants. 

Wild tobacco plants of the Nicotiana genus with higher concentrations of nicotine survived longer than sibling plants with lower concentrations. In other words, some plants evolved higher levels of nicotine because it benefited them. Although the primary purpose of the chemical in plants isn’t definitively known, studies have shown that at least one of its functions is to defend against attacking insects. 

However, nicotine’s effects in people are different from its role in plants. Since prehistoric times, people have recognized the stimulating effects of the smoke created by burning dried tobacco leaves. This effect comes from the way nicotine affects the brain.  

 

Nicotinic receptors and nicotine’s effect on the brain

Commercially available products, including cigarettes, nicotine replacement therapies (NRTs), smoke-free products, and others, contain levels of nicotine high enough to temporarily affect brain function in a reversible way.

Once inside the brain, nicotine binds to nicotinic acetylcholine receptors (nAChRs), such as those located on the brain’s nerve cells. These nAChRs are crucial receptors, involved in most communications between neurons in the brain but also outside the nervous system, such as between neurons and muscle cells.

The natural signaling molecule for nAChRs is acetylcholine, which nicotine can imitate as it binds to these receptors. When it does, it causes the release of neurotransmitters and hormones such as dopamine, GABA, glutamate, and noradrenaline. As a result, nicotine may stimulate and ultimately affect short-term brain functions regulated by these substances, such as emotion, learning, and memory. 

The action of nicotine in the brain can also trigger physiological effects outside the brain. For example, nicotine stimulates the release of the hormones epinephrine and norepinephrine into the bloodstream, leading to temporary narrowing of blood vessels, higher blood pressure, and increased heart rate. 

After repeated stimulation, the brain adapts to the presence of nicotine, a process that is reversible when a person stops using nicotine-containing products. This process of nicotine stimulation can ultimately lead to difficulty quitting.  

Continue learning about nicotine and addiction here.