Cannabis

Cannabis is the world’s most widely used illicit drug with 5–15% of young people in many western countries being regular cannabis users. Until the 1990s, the prevailing medical opinion was that cannabis use was nonaddictive and caused no long-term harm to health, brain, and brain function. This attitude has changed since, and current consensus is that regular cannabis use can result in dependence, increases the risk of using other illicit drugs, and is associated with increased mental health problems. However, it is still uncertain if these relationships are causal. There is, however, a steady increase in the number of people seeking help for cannabis-related problems. The increase in treatment demands has been linked to the high potency of nowadays cannabis products which may increase the risk of abuse and dependence. Cannabis affects the brain by interacting with the endogenous cannabinoid system which exists of cannabinoid receptors and their endogenous ligands. Acute intoxication with cannabis causes marked changes in subjective mental status (feeling high) and impairs cognition. These effects are accompanied by a number of bodily effects such as increased heart rate. The acute effects of cannabis on behavior, mood, and cognition are dose-dependent and biphasic (e.g., U-shaped pattern). There is still controversy regarding the persistence of effects of cannabis use on behavior, cognition, brain, and brain function once drug use has stopped. There is some evidence for subtle persisting effects, but these effects have predominantly been observed in certain vulnerable populations, i.e., individuals with either very long and very heavy exposure and/or very early onset of cannabis use, and/or comorbid conditions such as psychopathology.