The topic of marijuana addiction is emotionally charged. The two aspects of addiction—withdrawal symptoms unique to marijuana and alterations in the brain’s reward mechanism common to all addictive drugs—must be approached separately. THC’s stimulation of CB1 receptors causes a homeostatic reduction of receptor density, called downregulation. When THC stimulation wanes, the resultant relative lack of receptors leads to a transient deficiency of endocannabinoid activity. Hirnoven found a 20% reduction in endocannabinoid receptors in the cortex of individuals regularly using marijuana requiring 4 weeks of abstinence to be reversed. The effects of cannabinoid deficiency outlined by Budney include withdrawal symptoms of restlessness, anxiety, insomnia, boredom and irritability. Relapse to marijuana use often occurs to abort withdrawal symptoms. The influx of dopamine in the reward center (nucleus accumbens) caused by excessive cannabinoid stimulation is the sine qua non for addiction and leads to a neurologically based increase in the salience of marijuana. Modification of reward mechanisms increases the motivation to use marijuana to the point that cognitive rationality is clouded and denial is produced.

People often find statistics confusing because anecdotes more effectively tell stories and no one’s direct experience matches the statistical realities. The younger any individual is introduced to any drug the higher the risk of developing dependence. This is especially true for marijuana because it affects neurodevelopment in early adolescence. However, Horwood has shown than the lifetime rate of marijuana dependence does not accurately portray the overall progression of use because the majority of those who ever become dependent discontinue or reduce use sufficiently to no longer meet the DSM criteria for Cannabis Use Disorder (CUD). While 43% of those with onset of marijuana use at 13 years old meet criteria for CUD at some time by age 30, only 15% are dependent during the previous year at 30. The generally accepted rate of CUD for those 12 and older who have ever used marijuana is approximately 9%, compared to a 15% dependence rate for alcohol. The more frequently individuals use marijuana, the more they use on each occasion. The increased rates of marijuana use in Conduct Disorder (CD), Antisocial Personality Disorder (ASPD) and Attention Deficit Hyperactivity Disorder (jsADHD) are discussed.