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  1. 1. The Effects of Tetrahydrocannibinol on the Brain
  2. 2. Usage StatisticsSource: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. 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:
  4. 4. Methods of Action in the BrainIn the brain THC targets endocannabinoid receptors whichare normally used as receivers for naturally producedendocannabinoids.Specifically THC targets the CB1and CB2 receptorsThese receptors are found in various parts of the brain (seeimage below).
  5. 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 NaturalMedicines, March 21, 2010
  6. 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. “Decreasedwith prodromal symptoms of psychosis in drug.” Brazilian Journal of Medicine, April Depression in marijuana users.” Addictiveadoescence.” British Journal of Psychiatry, 2008. 2006. Behaviors, April 2006.
  7. 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 ofMarijuana Use in AdolescentsBefore and After Licit Drug Use:Examination of the GatewayHypothesis.” American Journal ofPsychiatry, 2006.
  8. 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-relatedmarijuana use: preliminary findings of a smaller brains.” New Scientist, June neurocognitive effects oflongitudinal study of effects on IQ in 2008. marijuana use.” Neurology,young adults.” Canadian Medical November 2002.Association Journal, April 2002.
  9. 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. 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.