addicted individual is so weakened that even
when he or she wants to cut down or stop using
an addictive substance, it becomes extremely
difficult to do so.^30
The Risk Factors for Addiction..........................................................................................
Genetic factors play a major role in the
development of addiction as do individual
biological and psychological characteristics and
environmental conditions.^31 These factors affect
both the initial use of an addictive substance and
the progression from initiation of substance use
to regular use to addictive use.^32
Whereas biological, psychological and
environmental factors--such as impairments in
the brain’s reward circuitry, compensation for
trauma and mental health problems, easy access
to addictive substances, substance use in the
family or media and peer influences--play a
large role in whether an individual starts to
smoke, drink or use other drugs,^33 genetic
factors are more influential in determining who
progresses to risky use or addiction.^34 A factor
that is particularly predictive of risk, however, is
the age of first use; almost all cases of addiction
begin with substance use before the age of 21,
when the brain is still developing.^35
Genetic Risks ...............................................................................................................
Twin and adoption studies* confirm a genetic
role in the likelihood of substance use and the
- These studies help distinguish the roles of genetics
and environment in the development of addiction.
Studies of adopted children allow researchers to
compare the adopted child both to her biological
parents with whom she shares genetic features but no
environmental experiences and to her adopted parents
with whom she shares environmental experiences but
no genetic features. Studies of identical and fraternal
twins allow researchers to isolate genetic similarities
development of addiction.^36 Although certain
specific genetic factors predispose an individual
to addiction involving a particular substance,^37
genetic factors also appear to contribute
generally to the risk of use and addiction.^38
Advances in genetic research have enabled
scientists to identify individual genes, including
genetic variations in components of the
dopamine transmission system,^39 implicated
both in the likelihood of substance use and of
addiction involving a variety of substances.^40Genetic variations may affect a person’s ability
to metabolize an addictive substance^41 or to
tolerate it.^42 Studies have found that genetics
account for between half and three quarters of
the risk for addiction.† 43 Genetic factors appear
to be stronger drivers than environmental factors
of initiation of substance use at an early age.^44Nicotine. Adolescents who do not have a
certain variant of the gene that is responsible for
the enzyme that metabolizes nicotine‡ progress
from smoking to addiction involving nicotine
faster than adolescents with that type of gene.^45
Other genetic variations in genes that determine
how nicotine receptors in the brain function§
also are linked to increased risk of addiction
involving nicotine and difficulty quitting
smoking.^46Alcohol. Individuals whose genetic makeup
influences them to have a higher tolerance for
alcohol are at increased risk of developingfrom environmental similarities. Identical twins are
genetically identical and fraternal twins share an
average of 50 percent of their genes, but both types of
twins typically experience a shared environment if
reared together.
† The majority of the genetics literature focuses on
addiction involving alcohol; the estimated extent of
genetic influence on addiction involving other drugs
varies by the type of drug.
‡ CYP2A6.
§ e.g., CHRNA5.People may choose to take drugs, but no one
chooses to be an addict.--Participant
CASA Columbia Focus Group
May 2008, Philadelphia, PA