NICOTINE ADDICTION

Nicotine Addiction
Addiction is defined as a situation in which a drug unreasonably controls behavior. The primary criteria for drug dependence are highly controlled or compulsive use of a drug with psychoactive effects and the presence of drug-reinforced behavior. Additional criteria are stereotypic patterns of use, use despite harmful consequences, relapse following abstinence, and recurrent drug cravings.

What are the symptoms of nicotine addiction?
•    irritability
•    impatience
•    hostility
•    anxiety
•    depressed mood
•    difficulty concentrating
•    restlessness
•    decreased heart rate
•    increased appetite or weight gain

Complications of Nicotine addiction?

Nicotine dependence can affect several parts of your body. Common complications of nicotine dependence are:

•    Lung cancer

•    Dry skin

•    Emphysema

•    Chronic bronchitis

•    Increased risk of heart disease.

•    Esophageal cancer

•    Larynx cancer

•    Throat cancer

•    Oral cancer

•    Infertility

•    Pregnancy and newborn complications

•    Dull senses

Dependence-producing drugs often produce “tolerance,” physical dependence, and pleasant effects. Smoking fits these definitions of an addictive behavior.  Approximately 40 percent of smokers attempt to quit annually, yet less than 5 percent do. Most smoking cessation tempts fail within the first two weeks; on average, four or more attempts are necessary before long-term cessation is achieved.

Even in patients with cardiovascular disease, cancer, or chronic obstructive pulmonary disease where stopping smoking is critical to halt further deterioration of their medical condition, fewer than 50 percent quit.

The agent largely responsible for maintaining smoking addiction is nicotine. Animal models demonstrate nicotine’s addictive potential, and several lines of evidence suggest that nicotine is addictive in humans as well. In addition to the difficulty in quitting, research shows that smokers adjust their smoking habits to maintain relatively stable concentrations of nicotine, that the reinforcing effects of nicotine are blocked by pretreatment with the nicotine receptor antagonist mecamylamine, and that quitting smoking is associated with cravings and a characteristic withdrawal syndrome. Nicotine’s neurobiological effects are complex and not entirely understood. Nicotine binds to nicotinic acetylcholine receptors located in the brain, autonomic ganglia, and neuromuscular junctions.

Such binding leads to the release of a number of neurotransmitters and hormones including dopamine, serotonin, norepinephrine, acetylcholine, vasopressin, and beta-endorphin. The release of these substances modulates many of the subjective, cognitive, and behavioral effects associated with smoking, such as increase in pleasure, improved mood, increased attention, enhanced cognition and motor performance, and weight loss.

Chronic use of nicotine results in the development of “tolerance,” which decreases the effect of a given dose of the drug. Tolerance is the result of morphological changes in the brain, such as receptor desensitization and inactivation as well as upregulation of receptor number. As a result of this neuroadaptation, cessation of tobacco use results in a withdrawal syndrome, characterized by depressed mood, insomnia, irritability, frustration or anger, anxiety, difficulty concentrating, restlessness, decreased heart rate, and increased appetite or weight gain. These symptoms generally peak at one week and gradually decrease over time, sometimes eventually reaching lower levels than were experienced while smoking. Thus, nicotine addiction is maintained not only by the subjective positive effects that smokers experience, but also by the desire to avoid the negative symptoms associated with nicotine withdrawal.

The potential for abuse or addiction to a drug is generally determined by the magnitude of the positive reinforcing effects and the speed of drug delivery to the brain. Typically, the relationship between drug dose and the reinforcing effect of the drug is characterized by an inverted U-shaped curve. Administration of an addictive drug will increase until its toxicity reduces the overall desirable effects and therefore decreases its reinforcing effects.

Generally, the more quickly the drug is delivered to the brain, the greater the potential for abuse. Nicotine from a smoked cigarette reaches the brain in ten to twenty seconds, with initial arterial nicotine concentrations far surpassing venous concentration.

Such rapid delivery contributes to its high abuse potential. Smokeless tobacco and nicotine gum, which take longer to reach the brain, have somewhat less abuse potential, and the nicotine patch, which is very slowly absorbed, has minimal abuse potential

Current and future pharmacological treatments aim to reduce tobacco use by targeting the mechanisms that reinforce tobacco use. Some treatments use agents that mimic the reinforcing effect of nicotine or reduce the negative effects (such as craving or withdrawal symptoms) associated with abstinence. Strategies being considered for future therapies include using agents that block the reinforcing effects of nicotine, prevent nicotine from crossing the blood brain barrier, and alter the metabolism of nicotine.

References

1. http://www.americanheart.org/presenter.jhtml?identifier=4753

2. http://www.mamashealth.com/substance/nicotine.asp