There are approximately 976 million smokers in the world. Estimates are that half of smokers (and one-third of former smokers) are dependent based on DSM criteria, regardless of age, gender or country of origin, but this could be higher if different definitions of dependence were used. Recent data suggest that, in the United States, the rates of daily smoking and the number of cigarettes smoked per day are declining, suggesting a reduction in population-wide dependence among current smokers. However, there are different groups of people who are more likely to smoke than the average population, such as those with low education or low socio-economic status and those with mental illness. There is also evidence that among smokers, some subgroups may be more dependent than other groups. Men smoke at higher rates than do women and score higher on dependence indices; however, women may be less likely to be successful in quitting, suggesting that women may be more dependent by that criterion. Higher nicotine dependence has also been linked with mental illness, including anxiety and depression.

Traditional cigarettes are the most common delivery device for nicotine. However, electronic cigarettes are becoming more popular. Nicotine can also be delivered via other tobacco products such as chewing tobacco, snus, pipe tobacco, hookah, all of which can produce nicotine dependence. The risk for developing dependence is related to how much nicotine is in a product and how fast it can get to the user’s brain. Smoke from products like cigarettes and hookah is absorbed in the lungs and then nicotine gets to the brain in about 6 seconds. Cigarettes and hookah also have large amounts of nicotine in them, and therefore people who use them have a higher risk of developing dependence. Products where nicotine is absorbed into the blood through the mouth (e.g., snus, chewing tobacco), and therefore takes longer to get to the brain, have lower dependence risk. Nicotine replacement medications like the nicotine patch, nicotine lozenges, and nicotine gum have minimal to no dependence risk because they do not contain nearly as much nicotine as tobacco products and they don’t get into the brain very quickly. This is why nicotine replacement medications are safe.

Most daily cigarette smokers have at least one of the above withdrawal symptoms when they try to stop. Withdrawal can occur in less-frequent users, however heavier users and those with a past or current psychiatric disorder tend to have more severe withdrawal. Genetics also influence the severity of withdrawal.

Various causes have been proposed to explain the causes of nicotine withdrawal. Nicotine binds to nicotinic receptors in the brain that, in turn, cause an increase in dopamine. Dopamine is the major chemical that stimulates reward centers in the brain. The brain recruits an opposing force to dampen the effects of nicotine and this causes tolerance (the reduction in the effect of nicotine). The onset of this opposing force and the fact that the brain becomes used to and dependent on nicotine to function normally is known as physical dependence. When nicotine intake is decreased, the brain's opposing force is now unopposed and this causes withdrawal symptoms. It also appears that opiate, serotonergic, glutamic, cannabinoid, and corticotrophin receptors may play a role in nicotine withdrawal.

The symptoms of stimulant use disorder include failure to control usage and frequency of use, an intense craving for the drug, increased use over time to obtain the same effects, known as a developed tolerance, and a continued use despite negative repercussions and interference in one’s everyday life and functioning. Furthermore, a disorder is noted when withdrawal symptoms occur because of a decrease in the drug amount and frequency, as well as stopping the use of the drug entirely. These withdrawal symptoms can last for days, weeks, months, and on rare occasions, years, depending on the frequency and dosages used by the individual. These symptoms include, but are not limited to, increased appetite, decreased energy, depression, loss of motivation and interest in once pleasurable activities, anxiety, insomnia, agitation and an intense craving for the drug. Unless intensive medical and psychological treatment is sought after, there is a very high likelihood of relapse among the user.

The long-term abuse of stimulants ultimately causes very serious medical issues, including but not limited to, addiction. Addiction, which is a disease that causes high rates of relapse, can be defined as a chronic disease that is characterized as a compulsive drug seeking behavior in which the user will stop at nothing to obtain the drug. Long time users of stimulants have noted changes in the body such as brain function, chemistry and molecular or cellular adaptations.

A number of studies have shown that tobacco use is a significant factor in miscarriages among pregnant smokers, and that it contributes to a number of other threats to the health of the fetus. It slightly increases the risk of neural tube defects.

Environmental tobacco smoke exposure and maternal smoking during pregnancy have been shown to cause lower infant birth weights.

Studies have shown an association between prenatal exposure to environmental tobacco smoke and conduct disorder in children. As well, post-natal tobacco smoke exposure may cause similar behavioral problems in children.

Women who smoke have about a 50% higher chance of giving birth to a child with behavioral disorders, such as ADHD, but a recent study in a book called "Attention Deficit Disorder: A Different Perception" overturns this, saying that ADHD is a genetic trait. Proof of this comes from a study showing that the people with ADHD had higher levels of certain hormones, as Thom Hartman explains with the hunter vs. farmer hypothesis.

Smoking is known to increase levels of liver enzymes that break down drugs and toxins. That means that drugs cleared by these enzymes are cleared more quickly in smokers, which may result in the drugs not working. Specifically, levels of CYP1A2 and CYP2A6 are induced: substrates for 1A2 include caffeine and tricyclic antidepressants such as amitriptyline; substrates for 2A6 include the anticonvulsant, valproic acid.

Examples (and ICD-10 code) include:

- F10.0 alcohol intoxication

- F11.0 opioid intoxication

- F12.0 cannabinoid intoxication

- F13.0 sedative and hypnotic intoxication (see benzodiazepine overdose and barbiturate overdose)

- F14.0 cocaine intoxication

- F15.0 caffeine intoxication

- F16.0 hallucinogen intoxication (See for example Lysergic acid diethylamide effects)

- F17.0 tobacco intoxication

The term contact high is sometimes used to describe intoxication without direct administration, either by second-hand smoke as with cannabis, or by placebo in the presence of others who are high.

Substance intoxication is a type of substance use disorder which is potentially maladaptive and impairing, but reversible, and associated with recent use.

If the symptoms are severe, the term "substance intoxication delirium" may be used.

Generic slang terms include: getting high or being stoned or blazed (all usually in reference to cannabis), with many more specific slang terms for each particular type of intoxicant. Alcohol intoxication is even graded in intensity, from buzzed, to tipsy, all the way up to hammered, smashed, wasted, destroyed, and a number of other similar terms.

Sudden infant death syndrome (SIDS) is the sudden death of an infant that is unexplainable by the infant's history. The death also remains unexplainable upon autopsy. Infants exposed to smoke, both during pregnancy and after birth, are found to be more at risk of SIDS due to the increased levels of nicotine often found in SIDS cases. Infants exposed to smoke during pregnancy are up to three times more likely to die of SIDS that children born to non-smoking mothers.

Smoking can also cause other birth defects, reduced birth circumference, altered brainstem development, altered lung structure, and cerebral palsy. Recently the U.S. Public Health Service reported that if all pregnant women in the United States stopped smoking, there would be an estimated 11% reduction in stillbirths and a 5% reduction in newborn deaths.

"Moderate alcohol consumption was associated with a lower risk of renal cell cancer among both women and men in this pooled analysis" "This pooled analysis found an inverse association between alcohol drinking and RCC. Risks continued to decrease even above eight drinks per day (i.e. >100 g/day) of alcohol intake, with no apparent levelling in risk."

A study concluded, "Results from our prospective cohort study of middle-aged and elderly women indicate that moderate alcohol consumption may be associated with decreased risk of RCC." Researchers who conducted a study in Iowa reported that "In this population-based case-control investigation, we report further evidence that alcohol consumption decreases the risk of RCC among women but not among men. Our ability to show that the association remains after multivariate adjustment for several new confounding factors (i.e., diet, physical activity, and family history) strengthens support for a true association.

Another study found no relationship between alcohol consumption and risk of kidney cancer among either men or women.

A Finnish study concluded, "These data suggest that alcohol consumption is associated with decreased risk of RCC in male smokers. Because most of the risk reductions were seen at the highest quartile of alcohol intake and alcohol is a risk factor for a number of cancers particularly among smokers, these data should be interpreted with caution." "Our data suggest an inverse association between alcohol intake and risk of renal cell cancer…" Compared with nondrinkers, men who drank one or more drinks per day had a 31% lower risk of kidney cancer among 161,126 Hawaii-Los Angeles Multiethnic Cohort participants.

A few studies have indicated an increased risk of neuroblastoma with use of alcohol during pregnancy.

The of nicotine is 50 mg/kg for rats and 3 mg/kg for mice. 0.5-1.0 mg/kg can be a lethal dosage for adult humans, and 0.1 mg/kg for children. However the widely used human LD estimate of 0.5–1.0 mg/kg was questioned in a 2013 review, in light of several documented cases of humans surviving much higher doses; the 2013 review suggests that the lower limit causing fatal outcomes is 500–1000 mg of ingested nicotine, corresponding to 6.5–13 mg/kg orally. An accidental ingestion of only 6 mg may be lethal to children.

It is unlikely that a person would overdose on nicotine through smoking alone. The US Food and Drug Administration (FDA) stated in 2013: "There are no significant safety concerns associated with using more than one [over the counter] OTC [nicotine replacement therapy] NRT at the same time, or using an OTC NRT at the same time as another nicotine-containing product—including a cigarette." Ingestion of nicotine pharmaceuticals, tobacco products, or nicotine containing plants may also lead to poisoning. Smoking excessive amounts of tobacco has also led to poisoning; a case was reported where two brothers smoked 17 and 18 pipes of tobacco in succession and were both fatally poisoned. Spilling an extremely high concentration of nicotine onto the skin can result in intoxication or even death since nicotine readily passes into the bloodstream following skin contact.

The recent rise in the use of electronic cigarettes, many forms of which are designed to be refilled with nicotine-containing "e-liquid" supplied in small plastic bottles, has renewed interest in nicotine overdoses, especially in the possibility of young children ingesting the liquids. A 2015 report on e-cigarettes by Public Health England noted an "unconfirmed newspaper report of a fatal poisoning of a two-year old child" and two published case reports of children of similar age who had recovered after ingesting e-liquid and vomiting. They also noted case reports of suicides by nicotine. Where adults drank liquid containing up to 1,500 mg of nicotine they recovered (helped by vomiting), but an ingestion apparently of about 10,000 mg was fatal, as was an injection. They commented that "Serious nicotine poisoning seems normally prevented by the fact that relatively low doses of nicotine cause nausea and vomiting, which stops users from further intake." Four adults died in the US and Europe, after intentionally ingesting liquid. Two children, one in the US in 2014 and another in Israel in 2013, died after ingesting liquid nicotine.

Nicotine poisoning tends to produce symptoms that follow a biphasic pattern. The initial symptoms are mainly due to stimulatory effects and include nausea and vomiting, excessive salivation, abdominal pain, pallor, sweating, hypertension, tachycardia, ataxia, tremor, headache, dizziness, muscle fasciculations, and seizures. After the initial stimulatory phase, a later period of depressor effects can occur and may include symptoms of hypotension and bradycardia, central nervous system depression, coma, muscular weakness and/or paralysis, with difficulty breathing or respiratory failure.

From September 1, 2010 to December 31, 2014, there were at least 21,106 traditional cigarette calls to US poison control centers. During the same period, the ten most frequent adverse effects to traditional cigarettes reported to US poison control centers were vomiting (80.0%), nausea (9.2%), drowsiness (7.8%), cough (7.2%), agitation (6.6%), pallor (3.0%), tachycardia (2.5%), diaphoresis (1.5%), dizziness (1.5%), and diarrhea (1.4%). 95% of traditional cigarette calls were related to children 5 years old or less. Most of the traditional cigarette calls were a minor effect.

Calls to US poison control centers related to e-cigarette exposures involved inhalations, eye exposures, skin exposures, and ingestion, in both adults and young children. Minor, moderate, and serious adverse effects involved adults and young children. Minor effects correlated with e-cigarette liquid poisoning were tachycardia, tremor, chest pain and hypertension. More serious effects were bradycardia, hypotension, nausea, respiratory paralysis, atrial fibrillation and dyspnea. The exact correlation is not fully known between these effects and e-cigarettes. 58% of e-cigarette calls to US poison control centers were related to children 5 years old or less. E-cigarette calls had a greater chance to report an adverse effect and a greater chance to report a moderate or major adverse effect than traditional cigarette calls. Most of the e-cigarette calls were a minor effect.

From September 1, 2010 to December 31, 2014, there were at least 5,970 e-cigarette calls to US poison control centers. During the same period, the ten most frequent adverse effects to e-cigarettes and e-liquid reported to US poison control centers were vomiting (40.4%), eye irritation or pain (20.3%), nausea (16.8%), red eye or conjunctivitis (10.5%), dizziness (7.5%), tachycardia (7.1%), drowsiness (7.1%), agitation (6.3%), headache (4.8%), and cough (4.5%).

Diet and lifestyle are major factors thought to influence susceptibility to many diseases. Drug abuse, tobacco smoking, and alcohol drinking, as well as a lack of or too much exercise may also increase the risk of developing certain diseases, especially later in life. Between 1995 and 2005 813,000 Australians were hospitalised due to alcohol

In many Western countries, people began to consume more meat, dairy products, vegetable oils, tobacco, sugary foods, Coca-Cola, and alcoholic beverages during the latter half of the 20th century. People also developed sedentary lifestyles and greater rates of obesity. In 2014 11.2 million Australians were overweight or obese Rates of colorectal cancer, breast cancer, prostate cancer, endometrial cancer and lung cancer started increasing after this dietary change. People in developing countries, whose diets still depend largely on low-sugar starchy foods with little meat or fat have lower rates of these cancers. Causes are not just from smoking and alcohol abuse. Adults can develop lifestyle diseases through behavioural factors that impact on them. These can be unemployment, unsafe life, poor social environment, working conditions, stress and home life can change a person’s lifestyle to increase their risk of developing one of these diseases.

In 2013 there were 147,678 deaths within Australia mostly from lifestyle diseases including smoking of tobacco, alcohol use and other drugs, violence and unhealthy weight have impacted on Australians' death rate. The leading cause of death of Australian males was heart disease with 11,016 deaths, followed by lung cancer with 4,995 deaths, and chronic pulmonary disease killing 3,572. All these conditions were mainly attributed to smoking, alcohol abuse or unhealthy lifestyle. In 2013 coronary heart disease was the leading cause of death in 8,750 women, mainly as a result of their lifestyle. Dementia and Alzheimer disease came second, affecting 7,277 females and thirdly, cerebrovascular disease, killing 6,368. These top three causes of deaths could be minimized through lifestyle changes within the Australian population.

Table Shows that ages of people dying and the top five diseases of which they are dying.

Factors associated with the increase of these conditions and illnesses ironically appear to be things that are a direct result of technological advances. They include:

- Less strenuous physical exercise, often through increased use of motor vehicles

- Irregular exercise as a result of office jobs involving no physical labor.

- Easy accessibility in society to large amounts of low-cost food (relative to the much-lower caloric food availability in a subsistence economy)

- More food generally, with much less physical exertion expended to obtain a moderate amount of food

- More high fat and high sugar foods in the diet are common in the affluent developed economies of the late-twentieth century

- Higher consumption of meat and dairy products

- Higher consumption of refined flours and products made of such, like white bread or white noodles

- More foods which are processed, cooked, and commercially provided (rather than seasonal, fresh foods prepared locally at time of eating)

- Prolonged periods of little activity

- Greater use of alcohol and tobacco

- Longer life-spans

- Reduced exposure to infectious agents throughout life (this can result in a more idle and inexperienced immune system [as compared to an individual that experienced relatively frequent exposure to certain pathogens in their time of life])

- Increased cleanliness. The hygiene hypothesis postulates that children of affluent families are now exposed to fewer antigens than has been normal in the past, giving rise to autoimmune diseases.

The code F11.5 is reserved for opioid-induced psychosis, and F17.5 is reserved for tobacco-induced psychosis, but neither substance is traditionally associated with the induction of psychosis.

The code F15.5 also includes caffeine-induced psychosis, despite not being specifically listed in the DSM-IV. However, there is evidence that caffeine, in extreme acute doses or when severely abused for long periods of time, may induce psychosis.

Usually this lesion is reversible if the tobacco habit is stopped completely, even after many years of use. In one report, 98% of lesions disappeared within 2 weeks of stopping tobacco use. The risk of the lesion developing into oral cancer (generally squamous cell carcinoma and its variant verrucous carcinoma) is relatively low. Indeed, veruccous carcinoma is sometimes term snuff dipper's cancer. In most reported cases, malignant transformation has occurring in individuals with a very long history of chewing tobacco or who use dry snuff.

Smokeless tobacco use is also accompanied by increased risk of other oral conditions such as dental caries (tooth decay), periodontitis (gum disease), attrition (tooth wear) and staining.

Psychotic states may occur after using a variety of legal and illegal substances. Usually such states are temporary and reversible, with fluoroquinolone-induced psychosis being a notable exception. Drugs whose use, abuse, or withdrawal are implicated in psychosis include the following:

STK is extremely common among smokeless tobacco users. Given the association with smokeless tobacco use, this condition tends to occur in adults. A national USA survey estimated an overall prevalence of 1.5% of all types of smokeless tobacco lesions, with males affected more commonly than females.

While risk factors vary with age and gender, most of the common chronic diseases in the US are caused by dietary, lifestyle and metabolic risk factors that are also responsible for the resulting mortality. Therefore, these conditions might be prevented by behavioral changes, such as quitting smoking, adopting a healthy diet, and increasing physical activity. Social determinants are important risk factors for chronic diseases. Social factors, e.g., socioeconomic status, education level, and race/ethnicity, are a major cause for the disparities observed in the care of chronic disease. Lack of access and delay in receiving care result in worse outcomes for patients from minorities and underserved populations. Those barriers to medical care complicate patients monitoring and continuity in treatment.

In the US, Minorities and low-income populations are less likely to access and receive preventive services necessary to detect conditions at an early stage.

The majority of US health care and economic costs associated with medical conditions are for the costs of chronic diseases and conditions and associated health risk behaviors. Eighty-four percent of all health care spending in 2006 was for the 50% of the population who have one or more chronic medical conditions (CDC, 2014).

Green Tobacco Sickness (GTS) is a type of nicotine poisoning caused by the transdermal absorption of nicotine from the surface of wet tobacco plants. Tobacco harvesters, whose clothing becomes saturated from tobacco wet with rain or morning dew, are at high risk of developing GTS. Workers can avoid getting this sickness by waiting to harvest until the tobacco leaves are dry, or by wearing a rain suit. Wet clothing that has come in contact with tobacco leaves should be removed immediately and the skin washed with warm soapy water.

Nicotine from other sources, including nicotine gum, a nicotine patch or electronic cigarette, or other tobacco products like cigarettes or smokeless tobacco, appears to reduce the risk of GTS due to the body adapting to the intake of nicotine.

Symptoms of GTS include nausea, vomiting, headache, dizziness, and severe weakness. These symptoms may be accompanied by fluctuations in blood pressure or heart rate. Abdominal cramping, chills, increased sweating, salivation and difficulty breathing are also common. The illness will resolve on its own within one to two days, but symptoms may be so severe as to require emergency medical treatment.

Worldwide there are an estimated 33 million tobacco farm workers, with a substantial proportion living in developing countries. A recent international review reported that between 8-89% of tobacco harvesters may be affected in the course of a season (this wide variation probably being due to differences between study methodologies as well as a range of working conditions). The long-term health outcomes for individuals exposed to nicotine transdermally for extended periods of time are not known.