Addiction Medicine: Closing the Gap between Science and Practice

The areas of the brain affected by this complex
disease are among those that are responsible for
survival--including the areas associated with
motivation, decision making, risk and reward
assessment, pleasure seeking, impulse control/
inhibition, emotion, learning, memory and stress
control.^15

In order to reinforce activities necessary for
survival, the brain produces feelings of pleasure
in response to the satisfaction of fundamental
drives such as hunger, thirst and sex.^16
Behaviors that lead to these rewards tend to be
reinforced and thus perpetuated over time.^17 On
a neurological level, this reinforcement is a
process carried out by chemical messengers that
flood the reward circuits of the brain.^18
Virtually all addictive substances affect the
pleasure and reward circuitry deep in the brain*
which is activated by the neurotransmitter
dopamine.† 19

• The mesolimbic reward system.
  † The neurotransmitter serotonin also is involved in

some forms of substance addiction; it plays a role in
motivated or directed actions such as attaining
addictive substances and also influences dopamine
levels in the brain. Hallucinogenic drugs like LSD
and Ecstasy target serotonin systems in the brain.

Addictive substances drive behavior by causing

the release of more dopamine within brain

reward circuits than almost all natural rewards

including those tied to food and sex.^20 With

repeated use of addictive substances, the brain

begins to expect this stimulation and an addicted

individual may experience intense desire or

cravings whenever the addictive substances are

not readily available and especially when the

individual is exposed to cues associated with

substance use.^21 Recent research points to

evidence that use of one addictive substance can

increase the risk of use of and addiction

involving another substance; for example,

nicotine use can prime the brain, making it more

susceptible to developing addiction involving

cocaine.‡ 22 Signals in the environment such as

seeing a drug-using friend or passing a bar, or

emotional signals such as feeling stressed or sad

also become associated with the addictive

substance and spur the drive to obtain it.^23

As use continues, the pleasure associated with

the dopamine release that results from the

ingestion of an addictive substance--or from its

anticipation--can become consuming to the point

where fundamental natural drives and associated

behaviors lose their value in comparison.^25

At the same time, the brains of substance-using

individuals may adapt to the unnaturally high

levels of dopamine that result from continued

substance use and may respond by reducing the

normal release of dopamine as well as the

number of dopamine receptors in the brain.^26

When this happens, the addictive substance may

become necessary just for the person to feel

normal.^27 Compared to non-substance users, the

brains of chronic substance users appear to have

lower baseline levels of dopamine, making it

difficult for them to achieve feelings of pleasure

from substance use and other behaviors that

once were pleasurable.^28

Changes in the function and structure of the

brain result in specific, compulsive behaviors

aimed at obtaining and using addictive

substances.^29 The cognitive control of an

‡ This study provides a biological mechanism for the

“gateway effect.”

Definition of Addiction

American Society of Addiction Medicine

Addiction is a primary, chronic disease of brain

reward, motivation, memory and related circuitry.

Dysfunction in these circuits leads to

characteristic biological, psychological, social and

spiritual manifestations. This is reflected in an

individual pathologically pursuing reward and/or

relief by substance use and other behaviors.

Addiction is characterized by inability to

consistently abstain, impairment in behavioral

control, craving, diminished recognition of

significant problems with one’s behaviors and

interpersonal relationships and a dysfunctional

emotional response. Like other chronic diseases,

addiction often involves cycles of relapse and

remission. Without treatment or engagement in

recovery activities, addiction is progressive and

can result in disability or premature death.^24