Marijuana is the most commonly used illicit drug in the United States.
A dry, shredded green/brown mix of flowers, stems, seeds, and leaves of
the hemp plant Cannabis sativa, it usually is smoked as a cigarette
(joint, nail), or in a pipe (bong). It also is smoked in blunts, which
are cigars that have been emptied of tobacco and refilled with
marijuana, often in combination with another drug. Use also might
include mixing marijuana in food or brewing it as a tea. As a more
concentrated, resinous form it is called hashish and, as a sticky black
liquid, hash oil. Marijuana smoke has a pungent and distinctive,
usually sweet-and-sour odor. There are countless street terms for
marijuana including pot, herb, weed, grass, widow, ganja, and hash, as
well as terms derived from trademarked varieties of cannabis, such as
Bubble Gum®, Northern Lights®, Juicy Fruit®, Afghani #1®, and a number
of Skunk varieties.

The main active chemical in marijuana is THC The membranes of certain
nerve cells in the brain contain protein receptors that bind to THC.
Once securely in place, THC kicks off a series of cellular reactions
that ultimately lead to the high that users experience when they smoke
marijuana.
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 movement(5).

Brain

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 use indicate some changes in the brain
similar to those seen after long-term use of other major drugs of
abuse. 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 system(6) and changes in the activity
of nerve cells containing dopamine(7). Dopamine neurons are involved in
the regulation of motivation and reward, and are directly or indirectly
affected by all drugs of abuse.

Other Health Effects

Some of marijuana?s adverse health effects may occur because THC
impairs the immune system?s ability to fight off infectious diseases
and cancer. In laboratory experiments that exposed animal and human
cells to THC or other marijuana ingredients, the normal
disease-preventing reactions of many of the key types of immune cells
were inhibited(16). In other studies, mice exposed to THC or related
substances were more likely than unexposed mice to develop bacterial
infections and tumors(17, 18).

Trouble remembering things
Sleepiness
Anxiety
Paranoia (feeling that people are ?out to get you?)
Altered time perception

Tremors (shaking)
Nausea
Headache
Coordination becoming worse
Breathing problems
Increased appetite
Reduced blood flow to the brain
Changes in the reproductive organs