There is no question that smoking is addictive. However not everyone is affected the same way. Some people are never able to kick the habit while others seem to be able to quit on a whim.
It is the nicotine in the tobacco that is addictive. This chemical is absorbed by the brain where it changes the brain chemistry and affects your mood. The interior of your lungs contains a very large surface area designed to absorb oxygen into the blood stream. This same area also absorbs nicotine very well giving the smoker a sudden rush of nicotine. The nicotine is carried directly to the brain with each puff.
The mid-brain is the area of your brain that controls your moods and emotions; it is this area of the brain that nicotine targets. The presence of nicotine causes a relaxing pleasant feeling, however the absence of nicotine causes mood swings including irritability, anxiety and cravings. A nicotine replacement system such as nicotine gum can help alleviate these feelings.
Every time a smoker smokes the rush of nicotine immediately affects the brain, this helps to reinforce the smoking habit. When a person is trying to quit smoking they have to deal with the physical nicotine addiction as well as the psychological addiction to the act of smoking. For most people it is the habit of smoking that is harder to break than the physical addiction to nicotine.
Most smokers have many psychological triggers linked to smoking. Some of the more common ones are driving, talking on the phone and right after a meal. These are so strong that people have been known to reach for a cigarette during these times up to several years after they have quit. Stressful situations will frequently trigger strong cravings as well.
Despite the fact that nicotine is always addictive the level of physical addiction can vary dramatically from one person to the next. There seems to be a genetic link to this. Some people metabolize nicotine far faster than others; these people will have a much stronger physical addiction than someone whose body metabolizes it slower. There is an enzyme created in the liver that breaks down the nicotine. People with lower amounts of this enzyme are less likely to smoke and if they do smoke they are more likely to be light smokers.
It is possible that there is even a genetic link to the psychological addiction. There is evidence that how you handle stress is at least partially controlled by genetics. Since smoking is often used to help people handle stress your genes could influence this side of the smoking habit.
Despite all of this it is possible to quit smoking, more and more people are kicking the habit every day. For some people it is fairly easy to quit where as others will find it very difficult and will probably try and fail several times before they are able to quit for good. There are medical treatments as well as counseling and therapy to help with all aspects of quitting.
Just like any other habit the longer you have been doing it the harder it is to quit. Young smokers may find it easier to quit since the habit is not as ingrained as in some one that has been smoking for twenty or more years. People who have been smoking longer though are frequently more aware of the cost of smoking and can be far more motivated to quit.