Heredity, Environment, Psychoactive Drugs
HOW PSYCHOACTIVE DRUGS AFFECT PEOPLE
This chapter first examines how drugs get to the brain and the ways
in which they affect brain chemistry. Drugs can be inhaled, injected,
absorbed through mucous membranes, swallowed, or absorbed through
the skin. Drugs are then distributed through the circulatory system until
they reach the brain where they will have their greatest effect. The drugs
are then metabolized, principally by the liver, and then excreted from the
body in the urine, through exhaled breath, or through sweat.
The nervous system consists of the peripheral nervous system
(autonomic and somatic) and the central nervous system (the brain and
spinal cord). Using evolutionary terminology, psychoactive drugs affect
both the old (primitive) brain and the new brain (mostly the prefrontal
cortex). The key circuit of the brain that drugs affect is the
reward/reinforcement pathway, especially the nucleus accumbens and
the amygdala. Drugs cause their effects by mimicking or modifying
neurotransmitters (e.g., dopamine, serotonin, norepinephrine, GABA).
Problems occur because the stop switch that shuts off the craving
becomes dysfunctional. Drugs affect the nervous system at the cellular
level, particularly the synaptic gap. An individual’s drug tolerance, tissue
dependence, withdrawal, and metabolism determine additional effects.
New research indicates “stay-stopped” switches in the brain that leads to
slips and relapses making it difficult for many to remain in continuous
abstinence from addictive substances.
FROM EXPERIMENTATION TO ADDICTION
Besides the desired effects of drugs, such as getting high, self-
medicating, creating energy, relieving pain, zoning out, or altering
consciousness, undesirable side effects occur, some of them minor,
some major, and some fatal.
The level of drug use abstinence, experimentation, social/recreational
use, habituation, abuse, and addiction depends not only on the amount,
frequency, and duration of drug use but on a person’s susceptibility to
addiction as determined by heredity and environment. Compulsive
behaviors, such as gambling and compulsive eating, also affect brain
chemistry. All these factors cause alterations in brain chemistry that can
affect a person for a few hours, a few days, or even a lifetime. Many of
these alterations can be seen with the assistance of new imaging