Steven Wright, MD, FAAFP Julius Metts, MD, FAAFP Private practice, Littleton, Colo (Dr. Wright); California Substance Abuse and Treatment Center, Department of Corrections and Rehabilitation, Corcoran (Dr. Metts) sleighwright@gmail.com
The authors reported no potential conflict of interest relevant to this article.
Cognitive effects of cannabis are a concern.The central nervous system is not fully myelinated until the age of 18, and complete maturation continues beyond that. Due to neuroplasticity, life experiences and exogenous agents may result in further changes. Cannabis produces changes in brain structure and function that are evident on neuroimaging.43 Although accidental pediatric intoxication is alarming, negative consequences are likely to be of short duration.
Regular use by youth, on the other hand, negatively affects cognition and delays brain maturation, especially for younger initiates.9,38,44 With abstinence, deficits tend to normalize, but they may last indefinitely among young people who continue to use marijuana.44
Dyscognition is less severe and is more likely to resolve with abstinence in adults,44 which may tip the scale for adults weighing whether to use cannabis for a medical purpose.45 Keep in mind that individuals may not be aware of their cognitive deficits,46 even though nearly all domains (from basic motor coordination to more complex executive function tasks, such as the ability to control emotions and behavior) are affected.44 A possible exception may be improvement in attention with acute use in daily, but not occasional, users.44 Highly focused attention, however, is not always beneficial if it delays redirection toward a new urgent stimulus.
Mood benefit? Research suggests otherwise.The psychiatric effects of cannabis are not fully understood. Users may claim mood benefit, but research suggests marijuana prompts the development or worsening of anxiety, depression, and suicidality.12,47 Violence, paranoia, and borderline personality features have also been associated with use.38,47 Amotivational syndrome, a disorder that includes apathy, callousness, and antisocial behavior, has been described, but the interplay between cannabis and motivation beyond recent use is unclear.48
Psychomotor impairment persists for at least 6 hours after smoking cannabis, at least 10 hours after ingesting it, and may last up to 24 hours.Lifetime cannabis use is related to panic,49 yet correlational studies suggest both benefit and problems for individuals who use cannabis for posttraumatic stress disorder.50 It is now well established that marijuana use is an independent causal risk factor for the development of psychosis, particularly in vulnerable youth, and that it worsens schizophrenia in those who suffer from it.51 Human experimental studies suggest this may be because the effect of THC is counteracted by CBD.52 Synthetic cannabinoids are even more potent anxiogenic and psychogenic agents than plant-based marijuana.19,20
