Effects of nicotine on the brain
As any smoker can tell you, nicotine is a remarkably addictive drug; only about seven percent of people who try to quit smoking on their own last at least one year. Nicotine is among the most heavily used addictive drugs in the country, in spite of the long-known facts regarding smoking’s potential to cause lung cancer and many other health problems.
Nicotine is one of the most heavily used addictive drugs in the U.S., and the leading preventable cause of disease, disability, and death. Cigarette smoking accounts for 90 percent of lung cancer cases in the U.S., and about 38,000 deaths per year can be attributed to secondhand smoke. Most cigarettes in the U.S. market today contain 10 milligrams (mg) or more of nicotine. The average smoker takes in 1 to 2 mg nicotine per cigarette when inhaling.
In 1989, the Surgeon General issued a report indicating that cigarettes and other forms of tobacco which contain nicotine (such as cigars, pipe tobacco, and chewing tobacco) are addictive. The report also determined that smoking was a major cause of stroke as well as the third leading cause of death in the U.S.
What Is Nicotine?
Nicotine is one of more than 4,000 chemicals found in the smoke from tobacco products; it is the primary component that acts on the brain. Smokeless tobacco products (for example, snuff and chewing tobacco) also contain many toxins as well as high levels of nicotine. Nicotine is a naturally occurring, colourless liquid that turns brown when burned and takes on the odour of tobacco when exposed to air. There are many species of tobacco plants, the tabacum species serving as the major source of today’s tobacco products. An extensive study shows it to have a number of complex and sometimes unpredictable effects on the brain and body.
Nicotine is absorbed through the skin and mucosal lining of the nose and mouth or in the lungs (through inhalation). Nicotine can reach peak levels in the bloodstream and brain rapidly, depending on how it is taken. Cigarette smoking results in nicotine reaching the brain within just 10 seconds of inhalation. Cigar and pipe smokers, on the other hand, typically do not inhale the smoke, so nicotine is absorbed more slowly through the mucosal membranes of their mouths (as is nicotine from smokeless tobacco).
Nicotine is addictive, which is why most smokers tend to do it regularly. Addiction is characterized by compulsive drug seeking and use, even at the risk of negative health consequences. Most smokers know that tobacco is harmful and express a desire to decrease or end use of it, with nearly 35 million people seriously attempting to quit each year. Unfortunately, most relapses within just a few days and less than seven percent of those who try to quit on their own achieve about a year of abstinence.
Besides nicotine’s addictive properties, other factors to consider include its easy availability, the small number of legal and social consequences of tobacco use and the sophisticated marketing and advertising methods of tobacco companies. These combined with nicotine’s addictive properties often lead to first use and, ultimately, addiction.
Recent research has shown how nicotine acts on the brain. Nicotine activates the circuitry that regulates feelings of pleasure, the so-called reward pathways. Research has shown that nicotine increases the levels of dopamine (a key brain chemical involved in mediating the desire to consume drugs) in the reward circuits of the brain. Nicotine’s pharmacokinetic properties have been found to enhance its abuse potential. Smoking cigarettes produces a rapid distribution of nicotine to the brain, with drug levels peaking within 10 seconds of inhalation. The acute effects of nicotine dissipate within a few minutes, causing the need to continue repeated intake throughout the day.
A cigarette is a very efficient and highly engineered drug-delivery system. A smoker can get nicotine to the brain very rapidly with every inhalation. A typical smoker will take 10 puffs on a lit cigarette over a period of five minutes. Thus, a person who smokes about one-and-a-half packs (30 cigarettes) each day gets 300 nicotine hits to the brain daily. These factors contribute considerably to nicotine’s highly addictive nature.
Using advanced neuroimaging technology, research is beginning to show that nicotine may not be the only psychoactive ingredient in tobacco. Scientists can see the dramatic effect of cigarette smoking on the brain and are finding a marked decrease in the levels of monoamine oxidase (MAO), an enzyme responsible for breaking down dopamine. The change in MAO must be caused by some tobacco smoke ingredient other than nicotine since nicotine itself does not dramatically alter MAO levels. The decrease in two forms of MAO, A and B, results in higher dopamine levels. The need to sustain the high dopamine levels results in the desire for repeated drug use.
How Does Nicotine Deliver Its Effect?
Nicotine acts as both a stimulant and a sedative. Immediately after exposure to nicotine, there is a “kick” caused in part by the drug’s stimulation of the adrenal glands and resulting discharge of epinephrine (adrenaline). The rush of adrenaline stimulates the body, causing a sudden release of glucose as well as an increase in blood pressure, heart rate, and respiration. Nicotine also suppresses insulin output from the pancreas, causing smokers to be slightly hyperglycemic. In addition, nicotine indirectly causes a release of dopamine in the brain regions that control pleasure and motivation. This reaction is similar to that seen with other abused drugs—such as cocaine and heroin—and is thought to underlie the pleasurable sensations many smokers experience. In contrast, nicotine can also exert a sedative effect, depending on the level of the smoker’s nervous system arousal and the dose of nicotine taken.
Repeated exposure to nicotine results in the development of tolerance, the condition in which higher doses of a drug are required to produce the same initial effect. Nicotine is metabolized fairly rapidly, disappearing from the body in a few hours. Therefore some tolerance is lost overnight and smokers often report that the first cigarettes of the day are the strongest and/or the “best.” Tolerance progresses as the day develops, and later cigarettes have less effect.
Cessation of Nicotine
Cessation of nicotine use is followed by a withdrawal period that may last a month or more and includes symptoms that can quickly drive people back to tobacco use. Nicotine withdrawal symptoms may begin within a few hours after the last cigarette and include irritability, sleep disturbances, craving, cognitive and attentional deficits and increased appetite. Symptoms generally peak within the first few days and may subside within a few weeks, though for some people, they may persist for months or longer.
An important and poorly understood component of the nicotine withdrawal syndrome is craving, an urge for nicotine that has been described as a major obstacle to successful abstinence and may persist for six months or longer. While the withdrawal syndrome is related to the pharmacological effects of nicotine, the severity of withdrawal symptoms can also be affected by psychological experiences. For some people, the feel, smell, and sight of a cigarette and the ritual of obtaining, handling, lighting, and smoking it are all associated with the pleasurable effects of smoking and can make withdrawal or craving worse. While nicotine gum and patches may alleviate the pharmacological aspects of withdrawal, cravings often persist.
What Are the Medical Consequences?
The medical consequences of nicotine exposure result from effects of both the nicotine itself and how it is taken. Tobacco use accounts for one-third of all cancers. Foremost among the cancers caused by tobacco is lung cancer—the number one cancer killer of both men and women. In 90 percent of all lung cancer cases, there is a link to cigarette smoking. Nicotine exposure has also been shown to result in the following:
- Lung diseases such as chronic bronchitis and emphysema
- Exacerbation of asthma symptoms
- Associated with cancers of mouth, kidney, oesophagus, pharynx, larynx, stomach, pancreas, cervix, ureter, and bladder
- Risk of heart disease including stroke, vascular disease, heart attack, and aneurysm
- Passive or secondary smoke increases risk for many diseases including lung cancer and cardiovascular disease in nonsmokers as well as increasing the severity of asthma in children and incidence of sudden infant death syndrome
- Female smokers tend to have an earlier menopause
- Female smokers who take oral contraceptives are more prone to cardiovascular and cerebrovascular diseases
- Pregnant smokers: increased risk of stillborn, premature, or low-birth-weight infants
- Children of women who smoked while pregnant: increased risk for developing conduct disorders
DSM-V Criteria for Tobacco Use Disorder:
Tobacco Use Disorder is common among people who use cigarettes and smokeless tobacco daily and is not common among people who do not use tobacco daily or who use nicotine medications. The disorder refers to a pattern of tobacco use that leads to clinically significant impairment or distress within a 12-month period. In order to be diagnosed with tobacco use disorder, two of the following symptoms must be identified:
- Tobacco is taken in larger dosage and/or for a longer period of time than intended
- There is a persistent desire and failed effort/failed attempt to reduce tobacco use
- A large amount of time goes into the procuring or using tobacco
- An overwhelming desire, urge, or craving to use tobacco
- The inability, due to tobacco use, to maintain obligations for one’s job, school, or home life
- Continued tobacco use in the face of social/interpersonal problems that result from, or are made worse by, the use of the stimulant
- Tobacco use becomes prioritized to such an extent that social, occupational, and recreational activities are either given up on completely or are reduced drastically
- Tobacco use occurs even in situations where it becomes physically hazardous for the individual
- Use of tobacco continues even with knowing the physical and psychological risks and exacerbations associated with it
- The large increase in the amount of tobacco is needed to achieve the wanted effect, or the same use of tobacco no longer reaches desired effect
- Withdrawal symptoms characteristic of tobacco use are present, or tobacco is taken to relieve or avoid withdrawal symptoms
Nicotine is highly addictive. The ingestion of nicotine results in a discharge of epinephrine from the adrenal cortex, causing a sudden release of glucose. Stimulation is followed by depression and fatigue, leading the abuser to seek more nicotine.
In addition to nicotine, cigarette smoke is primarily composed of gases (mainly carbon monoxide) and tar. The tar in a cigarette leads to a high risk of emphysema, lung cancer, and bronchial disorders. The carbon monoxide in the smoke increases the chance of cardiovascular diseases.
Due to nicotine’s addictive nature, including the aforementioned release of dopamine, smoking tobacco may easily become a habit. You may develop a routine surrounding the act of smoking, for example, smoking after every meal or in certain locations or under certain levels of stress. If you are to overcome the addiction to nicotine, you may have to change behaviours you associate with smoking.
Research suggests that a person should quit smoking gradually to lessen the severity of withdrawal symptoms. Rates of relapse are highest in the first few weeks and months and diminish considerably after three months.
Studies have shown that pharmacological treatment combined with psychological treatment (such as psychological support and skills training to get through high-risk situations) results in some of the highest long-term abstinence rates.
Smoking cessation can have an immediate positive impact on a person’s health; for example, a 35-year-old man who quits smoking will, on average, increase his life expectancy by 5.1 years.
Nicotine replacement therapies (NRTs), such as nicotine gum and the nicotine patch, were the first pharmacological treatments approved by the Food and Drug Administration (FDA) for use in smoking cessation therapy. NRTs deliver a controlled dose of nicotine to a smoker to relieve withdrawal symptoms during the smoking cessation process. They are most successful when used in combination with behavioural treatments. FDA-approved NRT products include nicotine chewing gum, the nicotine transdermal patch, nasal sprays, inhalers, and lozenges.
Bupropion and varenicline are two FDA-approved non-nicotine medications that effectively increase rates of long-term abstinence from smoking. Bupropion, a medication that goes by the trade name Zyban, was approved by the FDA in 1997 for use in smoking cessation. Varenicline tartrate (Chantix) targets nicotine receptors in the brain, easing withdrawal symptoms and blocking the effects of nicotine if people resume smoking.
Several other non-nicotine medications are being investigated for the treatment of tobacco addiction, including other antidepressants and an antihypertensive medication. Scientists are also investigating the potential of a vaccine that targets nicotine for use in relapse prevention.
On the Horizon: A Nicotine Vaccine
By binding nicotine in the bloodstream and thereby blocking its entry into the brain, the resulting reduction of reinforcing effects is expected to prevent relapse. Studies to date have shown that a nicotine vaccine is safe and capable of inducing the production of long-lasting antibodies that help prevent smoking relapse.
Behavioural interventions can play an integral role in nicotine addiction treatment, either in conjunction with medication or alone. They employ a variety of methods to assist smokers in quitting, ranging from self-help materials to individual cognitive-behavioural therapy. These interventions teach individuals to recognize high-risk smoking situations, develop alternative coping strategies, manage stress, improve problem-solving skills, as well as increase social support.
Specifically, these include avoiding smoking environments (and smokers) and requesting and receiving support from family and friends. The single most important factor, however, may be the coping skills for both short- and long-term prevention of relapse. Smokers need to learn behavioural and cognitive tools for relapse prevention and be able to apply those skills in a crisis.
Quitting smoking can be difficult. People can be helped during the time an intervention is delivered; however, most intervention programs are short-term (one to three months). Within six months, 75-80 percent of people who try to quit smoking relapse. Research has now shown that extending treatment beyond the typical duration of a smoking cessation program can produce quit rates as high as 50 percent at one year.
Using pharmacological treatments can double the odds of their success. However, a combination of pharmacological and behavioural treatments, for example combining the nicotine patch with group therapy, further improves chances.
- National Institute on Drug Abuse
- Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition