How Addictions Develop

In “What Is Addiction” section, we saw that people can be said to be addicted when they lose control over the use of a substance and continue that behavior despite negative consequences. In such a case, using the substance takes precedence over all other goals and responsibilities in the person’s life, often to the point of incarceration or death. We’ve also seen that not everybody who drinks or uses drugs ends up losing control. So how is it that some people become addicted and some don’t?

Because addiction is a multifaceted problem with many aspects, the answer to this question is simply, “Well, it depends . . .” So let’s see if we can get a grip on how addictions develop.

One way of thinking about addiction is to compare it to an infectious disease, like the flu. At the beginning of an outbreak of the flu, the virus is introduced into the population by one person. Since the flu is spread by airborne contact - sneezing and coughing - it begins to spread quickly. But does everyone who is exposed to the virus get the flu? No.

Does everyone who experiments with an addictive substance become an addict? No.

Let’s look at our comparison with the flu from an epidemiological standpoint. A number of factors are in play, and these can be put into three groups: host, environmental, and agent.

Host Factors
Some people inherit a tendency to develop addiction. We will examine the genetics of addiction in more detail later on in this section.

Psychological factors may also increase or decrease an individual’s vulnerability to becoming addicted. People with psychiatric disorders such as clinical depression or anxiety have a higher risk of developing addiction. People who come from disrupted homes or who have been abused are also more prone to develop addiction.

Some personality factors may make a person more likely to experiment or to use. Risk takers, people with poor impulse control or low stress tolerance, and people who have difficulty learning from negative consequences are at increased risk.

Environmental Factors
Environmental factors might include the cultural acceptance of social use of the substance, the availability of a substance in the community, the degree of criminality associated with use of the substance, and so on. Community prevention and education programs aim at modifying the environmental aspect of the spread of addiction.

An example of the importance of environmental factors is seen in the rise of crack cocaine addiction in the late 1980s.

Powder cocaine, which is used intranasally (being snorted) was readily available in the early 1980s, but was fairly expensive. Extracting the cocaine base from the powder form of the drug, called free-basing, allowed for intravenous and inhalation use - methods that intensified the high - but was a somewhat involved and dangerous chemical process requiring the use of highly flammable chemicals. (The actor Richard Pryor was severely burned while free-basing.) Some clever but diabolical individual discovered, however, that you could take powder cocaine, dissolve and dilute it, mix it with common household chemicals, and cook it in the microwave to produce a crystalline form of cocaine called “rock” or “crack” cocaine that could be smoked in a pipe for an immediate and intense, although brief, high. This was a marketing coup for the drug cartels, because someone could take a kilogram of cocaine and produce mountains of cocaine rocks that could be sold very cheaply. The going price for a rock in some urban locations dropped below a dollar, opening the market to younger and less affluent users. Crack rocks were also much easier to conceal and transport than bulkier drugs like marijuana. The use of crack spread like wildfire, and so, unfortunately, did the intense addiction that it causes.

Agent Factors
Agent factors, which relate to the specific characteristics of the disease-causing entity, are important in addiction, involving the addictiveness of the substance itself. Addictiveness is an estimate of a substance’s tendency to be abused and its ability to result in compulsive use regardless of other factors.

As we will see later, all classes of addictive substances that have been studied so far interact with a certain part of the brain, but some are more potent than others in their effects on that organ.

The route of administration of a particular substance is also an important agent factor. In general, the oral form of a drug is less addictive than the intravenous form, which is less addictive than the inhaled form.

This has to do with the speed at which the drug reaches the brain. When drugs are taken orally, they can take up to an hour or more to peak in the brain circulation. Drugs taken intravenously peak in the brain circulation within minutes, inhaled drugs within seconds. The rate at which the drug enters the brain contributes to the risk of an addiction developing. Studies have shown that the strength of the learning effect on primitive parts of the brain correlates more closely with the rate at which the drug’s concentration increases than it does with the total concentration at its peak.

When we look at all these factors - host, environment, and agent - we can see how they come together in a particular situation to determine whether an individual will develop addiction. Some examples follow.

Tom, Sr., had grown up in an alcoholic family. His father,
his father’s father, and all his uncles on his father’s side were
alcoholic. When Tom was a child, he decided that he would
never, ever drink alcohol. He remained a teetotaller all his
life. He was successful and prominent in his community and
church. His son, Tommy, also did not drink while living at home.
However, when Tommy went to college, he drank beer for the
first time at a fraternity party. That night he became extremely
intoxicated, and could not remember anything after the first one
or two beers. He began to drink on weekends and was soon
drinking daily. He was expelled from college when his grades
dropped to D’s and F’s.

Tommy’s roommate, Bob, had grown up in a family that had
no alcoholics except for one distant cousin. His parents drank
socially, and never to excess. Bob first drank some in high school
with friends, and continued to drink at frat parties in college.
At one point, while having problems with a girlfriend, he drank
heavily for a while, but after getting sick at a party he cut back
on his use. He continues to drink socially and only occasionally,
without serious consequences.


Tommy and Bob were both exposed to alcohol in an environment that encouraged drinking. However, Tommy had inherited a genetic vulnerability to alcoholism that was not apparent in his father because his father never allowed himself to be exposed to alcohol. Whereas Bob was able to moderate his use of alcohol after experiencing some unpleasant consequences, Tommy was not.

Angela began drinking at thirteen, and shortly after that began
using marijuana whenever it was available to her. By the time
she dropped out of high school, she was using drugs on a daily
basis, including marijuana, pain pills, tranquilizers, LSD, and
powder cocaine. She came from a disturbed home and was
abused and neglected as a child by her drug-addicted mother
and various stepfathers. By the time she was twenty-five, she was
using crack cocaine almost exclusively, because it gave her the
most intense high. She was living on the streets and supporting
herself through prostitution.
Tanya came from a stable working-class home; she was a good
student and active in her church youth group. No one in her
family had ever had problems with alcohol or drugs. She did
not drink or smoke at all while she was in high school. After
graduating from junior college and getting a secretarial job, she
began going out with friends, and drank a little at parties. A
man she was dating encouraged her to try some crack cocaine,
assuring her that she wouldn’t get hooked if she used it only
occasionally. However, within six months Tanya was using as
much crack as she could get three or four times a week. She
had lost her job and was living on the street supporting herself
through prostitution.


Angela and Tanya both ended up with tragic lifestyles that centered around the addiction to crack cocaine. But they came from very different backgrounds. In Angela’s case, crack eventually took over as her drug of choice, but she had both psychological and genetic factors that favored her developing an addiction. While Tanya had no psychological or genetic factors to push her into addiction, she became trapped by a very addictive substance.

In both of the preceding examples, the environment was favorable for drinking or using drugs. In Tommy’s case, host factors were critical - he inherited the risk of alcoholism from his father, even though his father never drank. In Angela’s case, host factors included her history of severe abuse, which led her to learn to use chemicals to affect her mood. But in Tanya’s case, there were very few host factors. What got her in trouble was an agent factor - the strong addictive nature of crack cocaine.

Elizabeth Connell Henderson, M.D.



Appendix A: Regulation of Addictive Substances

Appendix B: Sources of Additional Information

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