Long-term misuse of alcohol can cause a wide range of mental health problems. Severe cognitive problems are common; approximately 10 percent of all dementia cases are related to alcohol consumption, making it the second leading cause of dementia. Excessive alcohol use causes damage to brain function, and psychological health can be increasingly affected over time. Social skills are significantly impaired in people suffering from alcoholism due to the neurotoxic effects of alcohol on the brain, especially the prefrontal cortex area of the brain. The social skills that are impaired by alcohol abuse include impairments in perceiving facial emotions, prosody perception problems and theory of mind deficits; the ability to understand humour is also impaired in alcohol abusers. Psychiatric disorders are common in alcoholics, with as many as 25 percent suffering severe psychiatric disturbances. The most prevalent psychiatric symptoms are anxiety and depression disorders. Psychiatric symptoms usually initially worsen during alcohol withdrawal, but typically improve or disappear with continued abstinence. Psychosis, confusion, and organic brain syndrome may be caused by alcohol misuse, which can lead to a misdiagnosis such as schizophrenia. Panic disorder can develop or worsen as a direct result of long-term alcohol misuse.

The co-occurrence of major depressive disorder and alcoholism is well documented. Among those with comorbid occurrences, a distinction is commonly made between depressive episodes that remit with alcohol abstinence ("substance-induced"), and depressive episodes that are primary and do not remit with abstinence ("independent" episodes). Additional use of other drugs may increase the risk of depression. Psychiatric disorders differ depending on gender. Women who have alcohol-use disorders often have a co-occurring psychiatric diagnosis such as major depression, anxiety, panic disorder, bulimia, post-traumatic stress disorder (PTSD), or borderline personality disorder. Men with alcohol-use disorders more often have a co-occurring diagnosis of narcissistic or antisocial personality disorder, bipolar disorder, schizophrenia, impulse disorders or attention deficit/hyperactivity disorder (ADHD). Women with alcoholism are more likely to experience physical or sexual assault, abuse and domestic violence than women in the general population, which can lead to higher instances of psychiatric disorders and greater dependence on alcohol.

Warning signs of alcoholism include the consumption of increasing amounts of alcohol and frequent intoxication, preoccupation with drinking to the exclusion of other activities, promises to quit drinking and failure to keep those promises, the inability to remember what was said or done while drinking (colloquially known as "blackouts"), personality changes associated with drinking, denial or the making of excuses for drinking, the refusal to admit excessive drinking, dysfunction or other problems at work or school, the loss of interest in personal appearance or hygiene, marital and economic problems, and the complaint of poor health, with loss of appetite, respiratory infections, or increased anxiety.

Individuals with an alcohol use disorder will often complain of difficulty with interpersonal relationships, problems at work or school, and legal problems. Additionally, people may complain of irritability and insomnia. Alcohol abuse is also an important cause of chronic fatigue.

Signs of alcohol abuse are related to alcohol's effects on organ systems. However, while these findings are often present, they are not necessary to make a diagnosis of alcohol abuse. Signs of alcohol abuse show its drastic effects on the central nervous system, including inebriation and poor judgment; chronic anxiety, irritability, and insomnia. Alcohol's effects on the liver include elevated liver function tests (classically AST is at least twice as high as ALT). Prolonged use leads to cirrhosis and liver failure. With cirrhosis, patients develop an inability to process hormones and toxins. The skin of a patient with alcoholic cirrhosis can feature cherry angiomas, palmar erythema and — in acute liver failure — jaundice and ascites. The derangements of the endocrine system lead to the enlargement of the male breasts. The inability to process toxins leads to liver disease, such as hepatic encephalopathy.

Alcohol abuse can result in brain damage which causes impairments in executive functioning such as impairments to working memory, visuospatial skills, and can cause an abnormal personality as well as affective disorders to develop. Binge drinking is associated with individuals reporting fair to poor health compared to non-binge drinking individuals and which may progressively worsen over time. Alcohol also causes impairment in a person's critical thinking. A person's ability to reason in stressful situations is compromised, and they seem very inattentive to what is going on around them. Social skills are significantly impaired in people suffering from alcoholism due to the neurotoxic effects of alcohol on the brain, especially the prefrontal cortex area of the brain. The social skills that are impaired by alcohol abuse include impairments in perceiving facial emotions, difficulty with perceiving vocal emotions and theory of mind deficits; the ability to understand humour is also impaired in alcohol abusers. Adolescent binge drinkers are most sensitive to damaging neurocognitive functions especially executive functions and memory. People who abuse alcohol are less likely to survive critical illness with a higher risk for having sepsis and were more likely to die during hospitalization.

Alcohol abuse among pregnant women causes their baby to develop fetal alcohol syndrome. Fetal alcohol syndrome is the pattern of physical abnormalities and the impairment of mental development which is seen with increasing frequency among children with alcoholic mothers. Alcohol exposure in a developing fetus can result in slowed development of the fetal brain, resulting in severe retardation or death. Surviving infants may suffer severe abnormalities such as abnormal eyes, fissures, lips and incomplete cerebella. Some infants may develop lung disease. It is even possible that the baby throughout pregnancy will develop heart defects such as ventricular septal defect or atrial septal defect. Experts suggest that pregnant women take no more than one unit of alcohol per day. However, other organizations advise complete abstinence from alcohol while pregnant.

The long-term effects of alcohol (also known formally as ethanol) consumption range from cardioprotective health benefits for low to moderate alcohol consumption in industrialized societies with higher rates of cardiovascular disease to severe detrimental effects in cases of chronic alcohol abuse. Health effects associated with alcohol intake in large amounts include an increased risk of alcoholism, malnutrition, chronic pancreatitis, ], and cancer. In addition, damage to the central nervous system and peripheral nervous system can occur from chronic alcohol abuse. The long-term use of alcohol is capable of damaging nearly every organ and system in the body. The developing adolescent brain is particularly vulnerable to the toxic effects of alcohol. In addition, the developing fetal brain is also vulnerable, and fetal alcohol spectrum disorders (FASDs) may result if pregnant mothers consume alcohol.

The inverse relation in Western cultures between alcohol consumption and cardiovascular disease has been known for over 100 years. Many physicians do not promote alcohol consumption, however, given the many health concerns associated with it, some suggest that alcohol should be regarded as a recreational drug, and promote exercise and good nutrition to combat cardiovascular disease. Others have argued that the benefits of moderate alcohol consumption may be outweighed by other increased risks, including those of injuries, violence, fetal damage, liver disease, and certain forms of cancer. Alcohol liver disease (ALD) accounted for four fifths of all chronic diseases in Ireland in 2013.

Withdrawal effects and dependence are also almost identical. Alcohol at moderate levels has some positive and negative effects on health. The negative effects include increased risk of liver diseases, oropharyngeal cancer, esophageal cancer and pancreatitis. Conversely moderate intake of alcohol may have some beneficial effects on gastritis and cholelithiasis. Of the total number of deaths and diseases caused by alcohol, most happen to the majority of the population who are moderate drinkers, rather than the heavy drinker minority. Chronic alcohol misuse and abuse has serious effects on physical and mental health. Chronic excess alcohol intake, or alcohol dependence, can lead to a wide range of neuropsychiatric or neurological impairment, cardiovascular disease, liver disease, and malignant neoplasms. The psychiatric disorders which are associated with alcoholism include major depression, dysthymia, mania, hypomania, panic disorder, phobias, generalized anxiety disorder, personality disorders, schizophrenia, suicide, neurologic deficits (e.g. impairments of working memory, emotions, executive functions, visuospatial abilities and gait and balance) and brain damage. Alcohol dependence is associated with hypertension, coronary heart disease, and ischemic stroke, cancer of the respiratory system, and also cancers of the digestive system, liver, breast and ovaries. Heavy drinking is associated with liver disease, such as cirrhosis. Excessive alcohol consumption can have a negative impact on aging.

Recent studies have focused on understanding the mechanisms by which moderate alcohol consumption confers cardiovascular benefit.

Substance abuse, also known as drug abuse, is a patterned use of a drug in which the user consumes the substance in amounts or with methods which are harmful to themselves or others, and is a form of substance-related disorder. Widely differing definitions of drug abuse are used in public health, medical and criminal justice contexts. In some cases criminal or anti-social behavior occurs when the person is under the influence of a drug, and long term personality changes in individuals may occur as well. In addition to possible physical, social, and psychological harm, use of some drugs may also lead to criminal penalties, although these vary widely depending on the local jurisdiction.

Drugs most often associated with this term include: alcohol, cannabis, barbiturates, benzodiazepines, cocaine, methaqualone, opioids and some substituted amphetamines. The exact cause of substance abuse is not clear, with the two predominant theories being: either a genetic disposition which is learned from others, or a habit which if addiction develops, manifests itself as a chronic debilitating disease.

In 2010 about 5% of people (230 million) used an illicit substance. Of these 27 million have high-risk drug use otherwise known as recurrent drug use causing harm to their health, psychological problems, or social problems or puts them at risk of those dangers. In 2015 substance use disorders resulted in 307,400 deaths, up from 165,000 deaths in 1990. Of these, the highest numbers are from alcohol use disorders at 137,500, opioid use disorders at 122,100 deaths, amphetamine use disorders at 12,200 deaths, and cocaine use disorders at 11,100.

Chronic use of alcohol used to induce sleep can lead to insomnia: frequent moving between sleep stages occurs, with awakenings due to headaches and diaphoresis. Stopping chronic alcohol abuse can also lead to profound disturbances of sleep with vivid dreams. Chronic alcohol abuse is associated with NREM stage 3 and 4 sleep as well as suppression of REM sleep and REM sleep fragmentation. During withdrawal REM sleep is typically exaggerated as part of a rebound effect.

From the ICD-9 database:

- A chronic disease in which a person craves drinks that contain alcohol and is unable to control his or her drinking. A person with this disease also needs to drink greater amounts to get the same effect and has withdrawal symptoms after stopping alcohol use. Alcoholism affects physical and mental health, and can cause problems with family, friends, and work.

- A disorder characterized by a pathological pattern of alcohol use that causes a serious impairment in social or occupational functioning.

- A primary, chronic disease with genetic, psychosocial, and environmental factors influencing its development and manifestations. The disease is often progressive and fatal. It is characterized by impaired control over drinking, preoccupation with the drug alcohol, use of alcohol despite adverse consequences, and distortions in thinking, most notably denial. Each of these symptoms may be continuous or periodic. (morse & flavin for the joint commission of the national council on alcoholism and drug dependence and the american society of addiction medicine to study the definition and criteria for the diagnosis of alcoholism: in jama 1992;268:1012-4)

- For most adults, moderate alcohol use is probably not harmful. However, about 18 million adult Americans are alcoholics or have alcohol problems. Alcoholism is a disease with four main features:

- craving - a strong need to drink

- loss of control - not being able to stop drinking once you've started

- physical dependence - withdrawal symptoms, such as nausea, sweating, or shakiness when you don't drink

- tolerance - the need to drink greater amounts of alcohol to feel the same effect

- Temporary mental disturbance marked by muscle incoordination and paresis as the result of excessive alcohol ingestion.

According to the DSM-IV criteria for alcohol dependence, at least three out of seven of the following criteria must be manifest during a 12-month period:

- Tolerance

- Withdrawal symptoms or clinically defined alcohol withdrawal syndrome

- Use in larger amounts or for longer periods than intended

- Persistent desire or unsuccessful efforts to cut down on alcohol use

- Time is spent obtaining alcohol or recovering from effects

- Social, occupational and recreational pursuits are given up or reduced because of alcohol use

- Use is continued despite knowledge of alcohol-related harm (physical or psychological)

Binge drinking, or heavy episodic drinking, is a modern epithet for drinking alcoholic beverages with an intention of becoming intoxicated by heavy consumption of alcohol over a short period of time.

Binge drinking is a style of drinking that is popular in several countries worldwide, and overlaps somewhat with social drinking since it is often done in groups. The degree of intoxication, however, varies between and within various cultures that engage in this practice. A binge on alcohol can occur over hours, last up to several days, or in the event of extended abuse, even weeks. Due to the long-term effects of alcohol misuse, binge drinking is considered to be a major public health issue.

Binge drinking is associated with a profound social harm, economic costs as well as increased disease burden. Binge drinking is more common in males, during adolescence and young adulthood. Heavy regular binge drinking is associated with adverse effects on neurologic, cardiac, gastrointestinal, hematologic, immune, musculoskeletal organ systems as well as increasing the risk of alcohol induced psychiatric disorders. A US-based review of the literature found that up to one-third of adolescents binge-drink, with six percent reaching the threshold of having an alcohol-related substance use disorder. Approximately one in 25 women binge-drinks during pregnancy, which can lead to fetal alcohol syndrome and fetal alcohol spectrum disorders. Binge drinking during adolescence is associated with traffic accidents and other types of accidents, violent behavior as well as suicide. The more often a child or adolescent binge drinks and the younger they are the more likely that they will develop an alcohol use disorder including alcoholism. A large number of adolescents who binge-drink also consume other psychotropic substances.

Public health practitioners have attempted to look at substance use from a broader perspective than the individual, emphasizing the role of society, culture, and availability. Some health professionals choose to avoid the terms alcohol or drug "abuse" in favor of language they consider more objective, such as "substance and alcohol type problems" or "harmful/problematic use" of drugs. The Health Officers Council of British Columbia — in their 2005 policy discussion paper, "A Public Health Approach to Drug Control in Canada]" — has adopted a public health model of psychoactive substance use that challenges the simplistic black-and-white construction of the binary (or complementary) antonyms "use" vs. "abuse". This model explicitly recognizes a spectrum of use, ranging from beneficial use to chronic dependence.

Alcohol (also known as ethanol) has a number of effects on health. Short-term effects of alcohol consumption include intoxication and dehydration. Long-term effects of alcohol consumption include changes in the metabolism of the liver and brain and alcoholism. Alcohol intoxication affects the brain, causing slurred speech, clumsiness, and delayed reflexes. Alcohol stimulates insulin production, which speeds up glucose metabolism and can result in low blood sugar, causing irritability and possibly death for diabetics. A 2014 World Health Organization report found that harmful alcohol consumption caused about 3.3 million deaths annually worldwide.

However, some effects of alcohol consumption are beneficial. Although even moderate alcohol consumption increased the risk of death in younger people, it has been shown to "decrease" the risk of death for individuals ages 55+ (due to decreased risk of ischemic heart disease).

The median lethal dose of alcohol in test animals is a blood alcohol content of 0.45%. This is about six times the level of ordinary intoxication (0.08%), but vomiting or unconsciousness may occur much sooner in people who have a low tolerance for alcohol. The high tolerance of chronic heavy drinkers may allow some of them to remain conscious at levels above 0.40%, although serious health hazards are incurred at this level.

Alcohol also limits the production of vasopressin (ADH) from the hypothalamus and the secretion of this hormone from the posterior pituitary gland. This is what causes severe dehydration when alcohol is consumed in large amounts. It also causes a high concentration of water in the urine and vomit and the intense thirst that goes along with a hangover.

Stress, hangovers, and the oral contraceptive pill may increase the desire for alcohol because these things will lower the level of testosterone and alcohol will acutely elevate it. Tobacco has the same effect of increasing the craving for alcohol.

Nicotine dependence, or tobacco use disorder, is a state of dependence upon nicotine. There are different ways of measuring nicotine dependence. Some nicotine dependence assessments focus on key physical dependence outcomes like the development of tolerance which allows people to smoke heavily. Other assessments ask about psychosocial outcomes or underlying mechanisms of dependence. These different assessments either characterize dependence as a continuous construct or use cut-offs to diagnose whether or not a person is dependent.

Nicotine dependence is especially a concern among some populations such as those with co-occurring mental illness. There are evidence-based nicotine dependence treatments that include both medication and psychosocial interventions that can significantly increase a smoker’s chances of quitting successfully.

Stolle, Sack and Thomasius define binge drinking as episodic excessive drinking. There is currently no worldwide consensus on how many drinks constitute a "binge", but in the United States, the term has been described in academic research to mean consuming five or more standard drinks (male), or four or more drinks (female), over a 2-hour period. In 2015, the US Centers for Disease Control and Prevention, citing the National Institute on Alcohol Abuse and Alcoholism, defines binge drinking as "a pattern of drinking that brings a person’s blood alcohol concentration (BAC) to 0.08 grams percent or above. This typically happens when men consume 5 or more drinks, and when women consume 4 or more drinks, in about 2 hours." and estimated that about 16% of American adults met these binge drinking criteria four times per month. One 2001 definition from the publication "Psychology of Addictive Behavior" states that 5 drinks for men and 4 drinks for women must be consumed on one occasion at least once in a two-week period for it to be classed as binge drinking. This is colloquially known as the "5/4 definition", and depending on the source, the timeframe can vary. In the United Kingdom, binge drinking is defined by one academic publication as drinking more than twice the daily limit, that is, drinking eight units or more for men or six units or more for women (roughly equivalent to five or four American standard drinks, respectively). In Australia, binge drinking is also known as risky single occasion drinking (RSOD) and can be classified by the drinking of seven or more standard drinks (by males) and 5 or more standard drinks (by females) within a single day. When BEACH (Bettering the Evaluation of care and health) conducted a study which gathered information of people over the age of 18, it defined binge drinkers as those who consumed six or more standard drinks on one occasion whether that be weekly or monthly.

The above definitions are limited in that they do not take into account the time period over which the drinking occurs or the body mass of the person drinking. A person could be defined as a binge drinker even if he or she never becomes intoxicated. The term, however, has succeeded in drawing public awareness to the problem of excess drinking..

Other, less common definitions rely on blood alcohol concentration (BAC). For example, the National Institute on Alcohol Abuse and Alcoholism (NIAAA) defines the term "binge drinking" as a pattern of drinking that brings a person’s blood alcohol concentration (BAC) to 0.08 grams percent or above. Whatever the numerical definition used, heavy drinking or rapid consumption over a short period of time with the intention of becoming intoxicated is often implied when the term is used colloquially, since four or five drinks consumed over the course of a whole day and as an accompaniment to meals will not have the same effects as the same amount consumed over a couple of hours on an empty stomach.

An alternative colloquial term for binge drinking, "going on a bender", formerly implied a drinking spree of several days.

Nicotine dependence develops over time as a person continues to smoke. The risk for the development of dependence and how long it takes to become dependent differs from person to person; there is not a clear consensus on how long it takes for dependence to develop.

Nicotine dependence results in daily, heavy usage of cigarettes and produces withdrawal symptoms such as urges to smoke, negative moods, and difficulty concentrating, when the person stops smoking. These withdrawal symptoms are so unpleasant that smokers very frequently return to smoking. However, while it is known what nicotine dependence does—permits heavy smoking and causes severe withdrawal symptoms and relapse back to smoking—it is hard to measure nicotine dependence apart from these consequences.

Nicotine dependence has been classified as a chronic, relapsing disease. In other words, it is a long-term disorder that may have periods of relapse and remission that require repeated intervention, similar to other chronic conditions such as diabetes or hypertension. This perspective reinforces the idea that nicotine dependence is not a bad habit but an actual disease that requires ongoing treatment.

Alcohol-related brain damage is the damage that occurs to brain structures or function of the central nervous system as a result of the direct neurotoxic effects of alcohol intoxication or acute withdrawal. The frontal lobes are the most damaged region of the brains of alcohol abusers but other regions of the brain are also affected. The damage that occurs from heavy drinking/high blood alcohol levels causes impairments in judgement and decision making and social skills. These brain changes are linked to poor behavioural control and impulsivity, which tend to worsen the existing addiction problem.

The problems of alcoholism are well known, such as memory disorders, liver disease, high blood pressure, muscle weakness, heart problems, anaemia, low immune function, disorders of the digestive system and pancreatic problems as well as depression, unemployment and family problems including child abuse. Recently attention has been increasingly focused on binge drinking by adolescents and young adults due to neurochemical changes and brain damage which, unlike with alcoholism, can occur after a relatively short period of time; the damage is particularly evident in the corticolimbic region. This brain damage increases the risk of abnormalities in mood and cognitive abilities, increases the risk of dementia and additionally binge drinkers have an increased risk of developing chronic alcoholism.

Individuals who are impulsive are at high risk of addiction due to impaired behavioural control and increased sensation seeking behaviour. Alcohol abuse, especially during adolescence, causes a deterioration of executive functions in the frontal lobe. This brain damage from alcohol actually increases impulsivity and therefore worsens the addictive disorder.

There are five main stages of alcoholism. The first stage,occasional abuse and binge drinking, in this stage one may want to just experiment with alcohol and test their limits. These drinkers may be new to different forms of alcohol. This experimental stage is commonly seen in teens and young adults. These experimental drinkers also frequently engage in binge drinking. While they may not drink regularly, they consume exceptionally enormous amounts of alcohol at one time.

The second stage, increased drinking, in this stage one will leave the experimental stage and start drinking on a regular basis. Instead of just drinking at parties occasionally, one may find themselves drinking every weekend. Increased alcohol consumption can also lead to drinking for these reasons: as an excuse to get together with friends, to alleviate stress, out of boredom, or to combat sadness or loneliness.

The third stage, problem drinking, one will drink to get rid of their problems for them at any moment. As increased drinking continues, one becomes more dependent on alcohol and are at risk of developing alcoholism.

The fourth stage, alcohol dependence, this forms after the problem drinking stage. At this point, one has an attachment to alcohol that has taken over their regular routine. They are aware of the adverse effects, but no longer have control over their alcohol consumption. Alcohol dependence also means that one has developed a tolerance to drinking. As a result, they may have to consume larger quantities to get “buzzed” or drunk.

The fifth stage, addiction and alcoholism, this is the final and most harmful stage. One is addicted and dependent and must have alcohol all the time, if not they have withdrawals. Alcohol withdrawal is the changes the body goes through when a person suddenly stops drinking after prolonged alcohol abuse, or if one does not have alcohol for a period of time. Symptoms include trembling (shakes), insomnia, anxiety, and other physical and mental symptoms. If the alcohol is withdrawn suddenly, the brain is like an accelerated vehicle that has lost its brakes. Not surprisingly, most symptoms of withdrawal are symptoms that occur when the brain is overstimulated (Drugs.com). People with alcohol addiction physically crave the substance and are often inconsolable until they start drinking again. With prolonged abstinence neurogenesis occurs which can potentially reverse the damage from alcohol abuse.

The short-term effects of alcohol consumption range from a decrease in anxiety and motor skills at lower doses to unconsciousness, anterograde amnesia, and central nervous system depression at higher doses. Cell membranes are highly permeable to alcohol, so once alcohol is in the bloodstream it can diffuse into nearly every cell in the body.

The concentration of alcohol in blood is measured via blood alcohol content (BAC). The amount and circumstances of consumption play a large part in determining the extent of intoxication; for example, eating a heavy meal before alcohol consumption causes alcohol to absorb more slowly. Hydration also plays a role, especially in determining the extent of hangovers. After excessive drinking, unconsciousness can occur and extreme levels of consumption can lead to alcohol poisoning and death (a concentration in the blood stream of 0.40% will kill half of those affected). Alcohol may also cause death indirectly, by asphyxiation from vomit.

Alcohol can greatly exacerbate sleep problems. During abstinence, residual disruptions in sleep regularity and sleep patterns are the greatest predictors of relapse.

Cannabis withdrawal symptoms can occur in one half of patients in treatment for cannabis use disorders. These symptoms include dysphoria (anxiety, irritability, depression, restlessness), disturbed sleep, gastrointestinal symptoms, and decreased appetite. Most symptoms begin during the first week of abstinence and resolve after a few weeks.

According to the National Cannabis Prevention and Information Centre in Australia, a sign of cannabis dependence is that an individual spends noticeably more time than the average recreational user recovering from the use of or obtaining cannabis. For some, using cannabis becomes a substantial and disruptive part of an individual's life and he or she may exhibit difficulties in meeting personal obligations or participating in important life activities, preferring to use cannabis instead. People who are cannabis dependent have the inability to stop or decrease using cannabis on their own.

Cannabis use is associated with comorbid mental health problems, such as mood and anxiety disorders, and discontinuing cannabis use is difficult for some users. Psychiatric comorbidities are often present in dependent cannabis users including a range of personality disorders.

Common symptoms include:

- Sudden changes in behaviour – may engage in secretive or suspicious behaviour

- Mood changes – anger towards others, paranoia and little care shown about themselves or their future

- Problems with work or school – lack of attendance

- Changes in eating and sleeping habits

- Changes in friendship groups and poor family relationships

- A sudden unexplained change in financial needs – leading to borrowing/stealing money

There are many more symptoms such as physical and psychological changes, though this is often dependent on which drug is being abused. It is, however, common that abusers will experience unpleasant withdrawal symptoms if the drug is taken away from them.

It is also reported that others have strong cravings even after they have not used the drug for a long period of time. This is called being "clean". To determine how the brain triggers these cravings, multiple tests have been done on mice. It is also now thought that these cravings can be explained by substance-related disorders as a subcategory of personality disorders as classified by the DSM-5.

Include the following:

- Depression

- Shaking

- Feeling unreal

- Appetite loss

- Muscle twitching

- Memory loss

- Motor impairment

- Nausea

- Muscle pains

- Dizziness

- Apparent movement of still objects

- Feeling faint

- Noise sensitivity

- Light sensitivity

- Peculiar taste

- Pins and needles

- Touch sensitivity

- Sore eyes

- Hallucinations

- Smell sensitivity

All sedative-hypnotics, e.g. alcohol, barbiturates, benzodiazepines and the nonbenzodiazepine Z-drugs have a similar mechanism of action, working on the GABA receptor complex and are cross tolerant with each other and also have abuse potential. Use of prescription sedative-hypnotics; for example the nonbenzodiazepine Z-drugs often leads to a relapse back into substance misuse with one author stating this occurs in over a quarter of those who have achieved abstinence.

Signs and symptoms of opioid intoxication include:

- Decreased perception of pain

- Euphoria

- Confusion

- Desire to sleep

- Nausea

- Constipation

- Miosis

Signs and symptoms of opioid overdose include, but are not limited to:

- Pin-point pupils may occur. Patient presenting with dilated pupils may still be suffering an opioid overdose.

- Decreased heart rate

- Decreased body temperature

- Decreased breathing

- Altered level of consciousness. People may be unresponsive or unconscious.

- Pulmonary edema (fluid accumulation in the lungs)

- Shock

- Death

Substance abuse, also known as drug abuse, is a patterned use of a substance (drug) in which the user consumes the substance in amounts or with methods which are harmful to themselves or others.

The drugs used are often associated with levels of intoxication that alter judgment, perception, attention and physical control, not related with medical or therapeutic effects. It is often thought that the main abused substances are illegal drugs and alcohol; however it is becoming more common that prescription drugs and tobacco are a prevalent problem.

Substance-related disorders, including both substance dependence and substance abuse, can lead to large societal problems. It is found to be greatest in individuals ages 18–25, with a higher likelihood occurring in men compared to women, and urban residents compared to rural residents. On average, general medical facilities hold 20% of patients with substance-related disorders, possibly leading to psychiatric disorders later on. Over 50% of individuals with substance-related disorders will often have a "dual diagnosis," where they are diagnosed with the substance abuse, as well as a psychiatric diagnosis, the most common being major depression, personality disorder, anxiety disorders, and dysthymia.

A substance use disorder (SUD), also known as a drug use disorder, is a condition in which the use of one or more substances leads to a clinically significant impairment or distress. Although the term "substance" can refer to any physical matter, 'substance' in this context is limited to psychoactive drugs. Addiction and dependence are components of a substance use disorder and addiction represents the most severe form of the disorder.

A SUD involves the overuse of, or dependence on, a drug leading to effects that are detrimental to the individual's physical and mental health, or the welfare of others. An SUD is characterized by a pattern of continued pathological use of a medication, non-medically indicated drug or toxin, which results in repeated adverse social consequences related to drug use, such as failure to meet work, family, or school obligations, interpersonal conflicts, or legal problems.

There are ongoing debates as to the exact distinctions between substance abuse and substance dependence, but current practice standard distinguishes between the two by defining substance dependence in terms of physiological and behavioral symptoms of substance use, and substance abuse in terms of the social consequences of substance use. In the DSM-5 substance use disorder replaced substance abuse and substance dependence. Another term, substance-related disorder, has also been used.

In 2010 about 5% of people (230 million) used an illicit substance. Of these 27 million have high-risk drug use otherwise known as recurrent drug use causing harm to their health, psychological problems, or social problems or puts them at risk of those dangers. In 2015 substance use disorders resulted in 307,400 deaths, up from 165,000 deaths in 1990. Of these, the highest numbers are from alcohol use disorders at 137,500, opioid use disorders at 122,100 deaths, amphetamine use disorders at 12,200 deaths, and cocaine use disorders at 11,100.