What is chemical addiction?

Chemical addiction is a chronic, progressive and potentially fatal brain disease that is characterized by loss of control, denial and relapse. It is also marked by compulsive and continued use of substances despite harmful or negative consequences.

Why do some people become addicted to substances and others do not?

Different chemicals affect different brains in different ways.

On the surface, humans’ brains share certain physical characteristics. Adult brains all weigh about three pounds and are about six inches in diameter. But every brain works in different ways and scientists are still trying to figure out how those differences account for people’s susceptibilities to becoming addicted to alcohol and drugs. Some people are attracted to addictive substances from the first time they use them and find they want more. For other people, drugs or alcohol register negatively from the beginning and they have little or no desire for more.

A person’s vulnerability to becoming addicted appears to depend primarily on three factors:

Genetics. If an individual has relatives with histories of drug or alcohol problems, it may indicate that they face a heightened risk of developing addictions themselves.

Environment. The circumstances of how a person grows up and lives their lives – including their families, friends, peer pressures, stresses and their inherent fears and insecurities – can influence the risk of an individual misusing alcohol and drugs.

Age of first use. Science has found that the earlier a person starts using drugs or alcohol, the greater their risk of developing addictions.

Scientists are still searching for a better understanding of the complexities of the brain and about the disease of addiction. But experts concede that there is not yet a way of knowing in advance how a person may react to addictive substances before they put them into their bodies, or what longer-term risks of addiction they face.

The brain and chemicals

There are two components to chemical addiction: the brain and the chemicals. Once an addictive substance is introduced into a person’s body and makes its way to the brain, the interaction that occurs will determine if problems may result.

Fundamentally, alcohol and drugs initially cause a reaction that the brain interprets positively. Most produce euphoria or a sense of relief from tension and stress. They can heighten a person’s self-confidence, well-being and feeling of being in control. They can bring on a welcome feeling of drowsiness and sleep.

But alcohol and drugs, if misused, can also create a host of physical and emotional side effects that are detrimental, if not disastrous, to the user. Past the obvious physical effects of misusing substances such as a person slurring their words or losing their balance, addictive substances have emotional and intellectual consequences, too. They can erode rational thinking to the point where behaviors that a person knows are dangerous – driving a vehicle while drunk, for example, or becoming physically or verbally abusive to others – seem to make sense. A brain under the influence of drugs or alcohol can be affected physically, psychologically, emotionally and spiritually by those addictive substances.

This is why it’s often said that drugs and alcohol “hijack” the brain.

Here are substances most often misused and abused:

ALCOHOL (beer, wine, liquor and cordials)

  • By far, the most used and abused substance
  • Legal for purchasers over age 21, readily available, heavily advertised and socially acceptable
  • No. 1 gateway drug for youth

OPIOIDS (heroin, morphine, hydrocodone, oxycodone, fentanyl, codeine)  

  • Available both as legally prescribed painkillers and as illegal “street” drugs  
  • Eighty percent of Americans addicted to heroin began by using prescribed opioids
  • Combination of heroin laced with fentanyl has dramatically increased overdose deaths

STIMULANTS (amphetamines, methamphetamines, cocaine, crack cocaine, Ecstacy, Adderal, Ritilan)

  • Legally prescribed stimulants create energy, excitement and euphoria and can be highly addictive

DEPRESSANTS (prescribed sedatives and tranquilizers, benzodiazepines, Xanax, Valium, Ambien)

  • Excessive or long-term use can lead to addiction
  • Sometimes misused in conjunction with other substances to enhance sensations of euphoria or relaxation


  • Research suggests that chances of addiction in adulthood increase according to incidence of early usage
  • As with other potentially addicting substances, the risk of dependence on marijuana appears to hinge on how an individual’s brain interacts with the substance
  • Becoming more readily available as more states legalize marijuana for recreation use

We have provided only a limited overview of the most widely used and abused mild-altering chemicals. An abundance of further information is available about these and other addictive substances in our dropdown on addiction education.

Signs and symptoms

Sometimes, the signs and symptoms of an individual’s misuse of alcohol and drugs are easy to see: Unsteady gait, slurred speech, repeated absences from work, outbursts of belligerence or hostility, arrests for impaired driving, domestic violence incidents, serious health problems, etc.

Other times, individuals can go on for years successfully masking drug and alcohol problems from their closest friends, families, neighbors and employers. Perhaps, even from themselves. While the outward physical signs of these dependences can be harder to identify than in others, these individuals also suffer negative consequences because of their misuse of substances.

Since every brain is different and every brain reacts differently to different mind-altering substances, the signs and symptoms of an individual’s problem will be somewhat different.

But, in general, drugs and alcohol affect individuals in four chief ways: How they think (rationally), how they feel (emotionally), how they act (physically) and what they believe (spiritually). As a person’s use of drugs or alcohol deepens, the more the substances harm a person’s ability to function in all four areas.

People who develop dependencies on alcohol share several common signs and symptoms, which typically apply as well to those with drug-use problems:

  • Tolerance. Over time, more and more of the substance is needed to produce the same effect as the body builds tolerance to the chemicals.
  • Withdrawal. Anxiety, shakiness, insomnia, depression, fatigue and headaches are common signs of withdrawal when the body is deprived of substances it has become dependent on. For chronically heavy alcohol users, withdrawal without medical supervision can have life-threatening consequences.
  • Loss of control. Use of alcohol and drugs despite an individual’s promise to themselves or others that they will not do it.
  • Inability to stop. Efforts to stop and “stay stopped” fail.
  • Neglecting other activities. Once-valued, positive experiences such as exercise, reading, hobbies and sports are abandoned in favor of using alcohol and drugs.
  • Preoccupation with using substances. Thoughts about alcohol and drugs -- obtaining them in sufficient quantities, anticipating their use, using them and recovering afterward -- occupy increasing amounts of time, leaving less for more productive pursuits.

SAIR believes that the one warning sign for people to keep in mind about substance abuse – their own or others’ – is isolation. Isolation is the No. 1 factor that drives almost everything having to do with addiction. Virtually everyone who has become dependent on substances has withdrawn into themselves and into their own addictions. More and more, they have come to isolate themselves – emotionally, spiritually, even physically – from the things like family, friends, jobs, religion and other positive elements that defined their lives. This goes for both the person in the throes of a dependency problem and a sober person who is striving to avoid resuming alcohol or drug use.

Consequences and the ripple effect

The negative consequences of misusing alcohol and drugs are as varied as the individuals involved. In less-severe instances, they can be as relatively minor as saying something inappropriate to a co-worker or missing a child’s soccer match or music recital. In the most severe cases, substance abuse can lead to the loss of a job or custody of a child, destruction of a marriage, crime and incarceration, and death through accident, violence or disease.

Sooner or later, people who misuse or abuse alcohol and drugs almost always experience negative consequences. These tend to occur four ways:

  • Relationships. The individual’s dealings with spouses, children, relatives, colleagues, friends and neighbors weaken or are wrecked as alcohol and drug use increases.
  • Employment. Attention to jobs and careers wanes as a person’s interest in using substances deepens.
  • Legal. More severe substance use seems to also lead individuals to become embroiled in legal problems like arrests for drinking-and-driving or domestic violence, debt and bankruptcy. Researchers say that up to 80 percent of Americans who commit crimes abuse alcohol or drugs and half the inmates of U.S. prisons and jails are clinically addicted to substances. Alcohol is linked to the commission of more violent crimes than the use of illegal drugs.
  • Health. At the same time alcohol and drugs alter people’s behaviors, they also harm the health of individuals in a variety of well-documented ways. The Centers for Disease Control and Prevention estimates that about 88,000 Americans die each year due to the direct health consequences of excessive alcohol intake. However, an expanded study published by JAMA Network Open late in 2022 found that when the broader effects of drinking -- such as alcohol-related murders and accidents -- were factored in, an average of about 140,000 Americans died annually between 2015-19 from causes attributable to the consumption of alcohol. Among adults ages 20 to 49, the study found that 1 in 5 deaths were attributable to alcohol. There are also about 63,500 drug overdose deaths in the United States, according to the National Center for Health Statistics. A range of serious related health problems, from hypertension for heavy drinkers to neurological problems for drug users, are also associated with substance misuse and abuse.

While the consequences of misusing alcohol and drugs are usually negative, that does not mean they can’t be turned into a positive.

Consequences often provide the motivation people need to get help.

The presence or the threat of consequences can serve as a sign that alcohol or drugs are becoming a serious problem. Consequences can sometimes “scare” people into addressing their problems, as can the realization that they risk worse problems if they do not address their continued use of substances.  

But the individual using alcohol or drugs is not the only person affected. The “ripple effect” of alcohol and drugs often extends to the person’s spouse, children, grandchildren, parents, grandparents, siblings, friends, neighbors as well. Sometimes, the effects of a person’s substance abuse can be every bit as damaging emotionally, spiritually and financially to those close to the addict as it is to the addict themselves.

It’s often left to the person who is not in the throes of a substance problem to pick up the slack for those who are. They assume a greater share of child or parent care, home maintenance, money-earning and the other responsibilities that an addict becomes less and less able or inclined to do.

It is SAIR’s belief that substance abuse poses a problem that all people have a shared responsibility to help solve. It is the personal responsibility of the person with an alcohol or drug problem to seek help once it is apparent they need it. It is the responsibility of those close to the addict to help them do so. It is the responsibility of everyone to educate themselves about addiction and how to prevent it.

More about addiction

The U.S. Surgeon General’s report “Facing Addiction in America” contains an in-depth review of most known addictive substances, their effects on people’s health and options available for treating dependence on them.

The U.S. Surgeon General’s report also contains, in its executive summary, an accounting of how extensive a problem substance abuse is in America today and the toll it takes on the country economically and socially. In many ways, SAIR has found the Surgeon General’s report to be the most informative and effective resource available to get an overall view of substance in America today.

Since 1971, a simple, 25-question survey has been commonly used by health professionals to screen people for possible substance abuse and misuse problems. The Michigan Alcoholism Screening Test (MAST) can either be taken privately by an individual or administered by health care and social workers. It focuses on the level of a person's alcohol use and especially on difficulties they may have experienced because of it. 

The Mayo Clinic provides a comprehensive overview of substance misuse and addiction, including the nature of addiction as a brain disease and how to recognize signs of drug and alcohol misuse.

Helpguide.org is a California-based not-for-profit focusing on mental health, addiction and wellness issues. Its extensive materials on substance abuse describe the nature of addiction as brain disease and debunk myths about drug and alcohol use.

Father Joseph Martin (1924-2009) was a Roman Catholic priest and a recovering alcoholic whose lectures on substance abuse became standards for use in professional treatment programs beginning in the 1970s. His “Chalk Talk” and other presentations preserved on YouTube give you the opportunity to acquire the same excellent information about alcoholism and drug addiction that is still offered in many professional treatment programs today.