Nicotine is the central psychoactive compound found in tobacco, without which cigarettes would be little more than an expensive a stick of hay. Nicotine is the plant‘s natural protection against insects, but it is also the reason we reach for a cigarette when we are in a bad mood, or feeling stressed out - it is because this substance has the ability to both relax and stimulate our mind at the same time.
Once inhaled, nicotine quickly makes its way through the blood stream, reaching the brain in as little as 7 seconds. Once there, it activates the adrenal glands, causing the body to create extra epinephrine, also known more commonly as adrenaline. This causes the heart rate and blood pressure to increase, whilst perking up our central nervous system - making us feel more alert and active. Nicotine also stimulates the production of dopamine, a neurotransmitter that activates the pleasure pathways of the brain, making the experience more rewarding.
Depending on the individual constitution and the dosage, nicotine can also have sedative effects. Some research suggests that the calming effect is of psychological origin - it‘s the satisfaction of getting a nicotine fix that creates a sense of relaxation, but it‘s not actually the nicotine itself that directly causes it. In that sense, the relaxation is a secondary effect.
Additionally, nicotine raises blood sugar levels, which is thought to be a result of the extra adrenaline released. This extra glucose has been associated with increased learning ability, improved memory and higher levels of alertness. As commonly known, nicotine is also the substance that creates the addiction in cigarettes.
It is important to understand that cigarette smoke and nicotine are not the same things. Nicotine is a substance contained in cigarettes and the smoke they produce, but the smoke is filled with thousands of other chemicals and toxins. It is quite possible to obtain nicotine through other methods, such as e-cigarettes or nicotine patches, that avoid all of the other toxins, such as tar and carbon-monoxide, that come with smoking tobacco. Also, lung disease and other serious illnesses are primarily related to tobacco smoke, not the actual nicotine itself.