Marijuana usage is increasing, with over 50% of youth trying it. While smoking allows rapid brain absorption, consumption takes longer. THC in marijuana binds to endocannabinoid receptors in the brain, interfering with natural processes and causing varied effects. Studies on marijuana's mental health and addiction risks are mixed, but heavy usage is clearly linked to brain shrinkage and potential permanent damage. More research is still needed to fully understand marijuana's effects.

1. The Effects of Tetrahydrocannibinol
on the Brain

2. Usage Statistics
Source:2002 National Survey on Drug Use and Health (NSDUH)
Source: 2010 NSDUH
Marijuana is more prevalent than any other type of illicit drug and it is
increasing in the overall number of users who have tried it.

3. Methods of usage and Reaching the Brain
• Marijuana is most commonly smoked, but it is also sometimes ingested.
• Smoking involves rapid absorption of THC (the main psychoactive agent in
marijuana) as it is absorbed in the alveoli in the lungs and travels through
the bloodstream to the brain in just a few seconds after inhalation.
• Consumption of cannabis takes longer, as it must first be absorbed in the
stomach, travel to the liver and then to the rest of the brain.
Source: Howstufforks.com

4. Methods of Action in the Brain
In the brain THC targets endocannabinoid receptors which
are normally used as receivers for naturally produced
endocannabinoids.
Specifically THC targets the CB1and CB2 receptors
These receptors are found in various parts of the brain (see
image below).

5. Methods of Action in the Brain (cont.)
• The main effects of marijuana are caused by its target of CB1 receptors,
as these are found primarily in the brain while CB2 receptors are found
primarily in the immune system.
• Once bound to the CB1 receptors THC interferes with the binding of
natural cannabinoid receptors and causes a decrease in adenylyl cyclase
activity, inhibition of calcium channels and reduced inhibition of
potassium channels.
• As a result of the widespread locations of endocannabinoid receptors for
THC to target, marijuana can have a variety of effects ranging from
euphoria and introspection to paranoia and increased appetite.
Source: Cancer and Natural
Medicines, March 21, 2010

6. Long-Term Effects of Marijuana
Use(Mental Health Correlation)
• A large-scale study in Britain1 found that there was a significantly
higher risk (1.5 times greater) of psychosis among adolescents who
used marijuana than among those that haven’t.
• But a recent study2 suggested that cannabidiol (a component of
marijuana) is effective as an antipsychotic drug.
• Another study3 found that depressed marijuana users reported less
symptoms of depression than non-users with depression.
+ =
1. Miettunen, Jouko. “Assosiaction of cannabis use 2. Zuardi, A.W. “Cannabidiol, a Cannabis
sativa constituent, as an antipsychotic 3. Denson, Thomas. “Decreased
with prodromal symptoms of psychosis in
drug.” Brazilian Journal of Medicine, April Depression in marijuana users.” Addictive
adoescence.” British Journal of Psychiatry, 2008.
2006. Behaviors, April 2006.

7. Long-Term Effects of Marijuana Use
(Gateway Drug)
• One common attack on marijuana has been its effect
as a gateway drug, either through social factors or
physiological changes made to brain chemistry by the
drug itself.
• However, a recent study4 found that adolescents who
used marijuana were no more likely to develop a
substance abuse issue than those who did not.
4. Tarter, Ralph. “Predictors of
Marijuana Use in Adolescents
Before and After Licit Drug Use:
Examination of the Gateway
Hypothesis.” American Journal of
Psychiatry, 2006.

8. Long Term Effects of Marijuana Use
(Brain Damage)
• There have been mixed results from studies performed
regarding marijuana and intelligence. A study5 found
no decrease in IQ in those who smoked lightly or
moderately, but there was a decrease in heavy users.
• Another study6 however found significant shrinkage in
the hippocampus (12%, controls memory and emotion)
and the amygdala (7.1%, controls fear and aggression).
• However a separate study7 found that any damage is
reversible except in heavy users.
5. Fried, Peter. “Current and former 6. “Heavy pot smoking linked to 7. Bolla KI. “Dose-related
marijuana use: preliminary findings of a smaller brains.” New Scientist, June neurocognitive effects of
longitudinal study of effects on IQ in 2008. marijuana use.” Neurology,
young adults.” Canadian Medical November 2002.
Association Journal, April 2002.

9. Long Term Effects of Marijuana Use
(Addiction)
• Cannabis withdrawal has been studied8, and
withdrawal usually lasts for 10-14 days and is
associated with irritability and anxiety along
with decreased appetite, indicating there that
there is at least some physical dependence
associated with marijuana usage
8. Kouri, Elena M. “Abstinence symptoms during
withdrawal from chronic marijuana use.”
Experimental and Clinical Psychophramacology,
Nov 2000.

10. Conclusions
• The main conclusion here is that marijuana still
requires additionally study. Many of the results found
are conflicting or inconclusive, and even strong
correlations do not necessarily show causation.
• The one thing that is clear is that heavy marijuana
usage is bad for the brain. It causes shrinkage of
important parts of the brain and heavy enough usage
can make this damage permanent.
• Given that over 50% of youths will try marijuana at
some point during their lifetime, and this trend seems
to be increasing rather than decreasing, the need for
greater understanding in this area is definite.