Nicotine Dependence: How it Happens
What Is Nicotine?
Nicotine is the drug in tobacco that causes dependence. Nicotine addiction, or dependence, is the most common form of chemical dependency in the nation. Research has suggested that nicotine is equally as addictive as heroin, cocaine, and alcohol. 
Every smoker is addicted to a different combination of the “stimulants” in cigarettes, making their personal experience with smoking and nicotine dependence unique. A stimulant is the addictive property in a cigarette that makes you crave more. 
Physical Effects of Nicotine
When you first start smoking you may experience nausea, dizziness, headache, or upset stomach, but over time, as your smoking becomes more of a habit, you build up a tolerance to these effects until they become unnoticeable. Tolerance means that it takes more nicotine to get the same effect that we used to get from fewer cigarettes. 
Routine smoking causes our bodies to adapt to having a certain level of nicotine; without realizing it, we regulate the number of cigarettes we smoke in order to maintain our bodies’ familiarized nicotine level. Our bodies’ tolerance to the unpleasant effects of nicotine allows us to focus on the pleasurable effects nicotine delivers. What most don’t realize, is that the pleasurable effects experienced from smoking, is the body’s reaction to the nicotine, which disrupts the body’s natural balance. 
After the habit of smoking is established, we feel as though we need to smoke to feel “normal”, like our daily tasks cannot be completed until we’ve had our smoke. We begin to connect our smoking routines with many of our daily and social activities, creating triggers, making it hard to do those activities without smoking. An example is associating a cigarette with a cup of coffee or talking on the phone. We usually aren’t aware of the psychological effects of smoking. The triggers, the feelings of relaxation, stress reduction, focus etc. become automatic. This is defined as psychological dependence. 
When you don’t smoke for a period of time, and no nicotine is entering the body, you can experience unpleasant physical and psychological side-effects such as intense cravings for nicotine, anxiety, depression, weight gain, headaches, problems concentrating, drowsiness or trouble sleeping, and feeling tense, restless, or frustrated. These symptoms are called withdrawal effects. [9, 11]
Whether or not you have these side effects, or to what degree, depends on how long, how much and how often you’ve smoked, and varies from person to person. Symptoms of nicotine withdrawal can begin anywhere from 2 hours to 2-3 days after your last cigarette. 
These side effects are a sign of physical dependence on nicotine. To relieve these withdrawal symptoms, it helps to gradually lessen the amount of nicotine you absorb during the quitting process by using pharmacological aids. These are prescription or over-the counter products that contain small amounts of nicotine to lessen withdrawal symptoms that may occur during the quitting process. (link OTC drug section). 
Psychological and physical dependence, as well as withdrawal, are defining characteristics of a drug addiction. More often than not, society treats smoking as an optional activity, when in reality, most smokers continue to smoke because they are dependent upon nicotine, and are not smoking out of choice, but out of habit and need for the drug. Every single person who smokes shows signs of physical and psychological dependence on nicotine. [11, 12]
How Does the Body Become Dependent on Nicotine?
Every time we light up, nicotine and other chemicals from cigarette smoke are absorbed in the body. Nicotine enters the bloodstream and reaches the brain faster than drugs that enter the body through our veins. Nicotine affects many parts of the body; it changes how the body uses food (metabolism), causes our heart to beat faster, our pulse to quicken, it increases our blood pressure, and our veins begin to tighten causing blood flow throughout the body to become more difficult. 
Nicotine works by stimulating our nervous system to release specific chemical messengers (hormones and neurotransmitters) that affect different parts of our brain and body. One hormone that nicotine affects is epinephrine, also known as adrenaline. When nicotine is inhaled, the buzz you feel is the release of epinephrine which stimulates the body and causes your blood pressure and heart rate to increase, and makes you breathe harder. Nicotine also activates a specific part of your brain that makes you feel happy by stimulating the release of the hormone dopamine. The release of dopamine when nicotine is inhaled is thought to be the source of the pleasurable sensations you experience when smoking, which can include relaxation, a buzz, and relief of tension.
Once inhaled, nicotine is rapidly distributed throughout the brain within 10 seconds. The enjoyable feelings you experience from smoking occur very quickly, but after you’ve smoked a few times nicotine begins to weaken your ability to feel pleasure, causing you to need more nicotine in order to sustain the good feelings. This is the cycle of the smoking habit; in order to continue feeling pleasure from smoking, you must continue to smoke more cigarettes, more frequently. [13-16]