Chapter 4 - Epidemiology

Summary

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.