Scientists have learned a great deal about how THC acts in the
brain to produce its many effects. When someone smokes marijuana,
THC rapidly passes from the lungs into the bloodstream, which
carries the chemical to organs throughout the body, including the brain.
In the brain, THC connects to specific sites called cannabinoid
receptors on nerve cells and influences the activity of those cells.
Some brain areas have many cannabinoid receptors; others have few or
none. Many cannabinoid receptors are found in the parts of the brain
that influence pleasure, memory, thought, concentration, sensory and
time perception, and coordinated movement4.
The short-term effects of marijuana can include problems with
memory and learning; distorted perception; difficulty in thinking
and problem solving; loss of coordination; and increased heart rate.
Research findings for long-term marijuana abuse indicate some changes
in the brain similar to those seen after long-term abuse of other major
drugs. For example, cannabinoid (THC or synthetic forms of THC)
withdrawal in chronically exposed animals leads to an increase in
the activation of the stress-response system5 and changes in the
activity of nerve cells containing dopamine6. Dopamine neurons are
involved in the regulation of motivation and reward, and are directly
or indirectly affected by all drugs of abuse.