Cognitive Toxicity of Cannabis: The Devil Is in the Confounding Variables
Harrison G. Pope, Jr., M.D.

SUMMARY: Dr. Harrison Pope presented an overview of the difficulties in determining whether observed cognitive deficits are attributable to toxic effects of cannabis itself by long-term, heavy cannabis abusers, or simply to confounding factors associated with heavy cannabis use. At present, it appears reasonable to conclude that deficits in attention and memory persist for at least several days after discontinuing regular heavy cannabis use. It is less clear, however, whether heavy cannabis use can cause neurotoxicity that persists long after discontinuation of use, or whether cognitive deficits magnify with increasing lifetime cannabis exposure.

Cognitive Effects in Adolescents Exposed Prenatally to Marijuana or Cigarettes
Peter A. Fried, Ph.D.

SUMMARY: Dr. Peter Fried discussed the consequences of prenatal exposure to marijuana on aspects of cognitive functioning and visual analysis/hypothesis testing in early and late adolescent offspring as described in a middle-class, low-risk sample that was studied prospectively from birth. These data were compared to the effect of prenatal cigarette exposure on the same sample. Fried concluded that the consequences of fetal marijuana exposure are subtle and appear not to have a deleterious effect on global intelligence, but rather on aspects of executive functioning. In contrast, in-utero exposure to cigarettes showed effects on overall intelligence, particularly with many aspects of verbal performance.

Effects of Chronic Marijuana Use and THC on Brain Function in Humans: An fMRI Study
Alan S. Bloom, Ph.D.

SUMMARY: Dr. Alan Bloom’s goal was to improve the understanding of THC’s effect on certain sites of action in the human brain and how these sites are involved in the drug’s effects. His team studied, in frequent marijuana users, the effects of doses of THC that produce subjective effects similar to those seen with marijuana use in a social situation on regional brain activity using BOLD and arterial spin labeling (ASL) fMRI techniques. Significant findings include: (1) THC produces a dose-related increase in the activity of the nucleus accumbens, (2) THC administration decreases brain activation induced by the performance of both cognitive and motor tasks, and (3) global brain perfusion was greater in frequent marijuana users than nondrug-using control subjects. Bloom demonstrated that THC produces significant effects on brain activity and cognitive task-induced activation at doses that produce effects similar to those produced by marijuana in a social situation.

Behavioral and Treatment Research on Marijuana Withdrawal and Dependence
Alan J. Budney, Ph.D.

SUMMARY: Dr. Alan Budney provided highlights from six clinical studies on marijuana dependence, withdrawal, and treatment. The first was a 1999 Withdrawal Study providing information on 54 adults seeking treatment for marijuana dependence. Another study was a 2003 Timecourse Study in which data were collected for withdrawal discomfort, restlessness, aggression, weight change, and strange dreams. The third study outlined was the “Pharmacological Specificity Dronabinol (Oral THC) Attentuates Marijuana Withdrawal” study. Budney’s presentation ended with a summary of treatment outcome research to date. He discussed three treatment studies: the Marijuana Treatment project—a behavioral treatment study comparing behavioral coping-skills therapy (BT), BT plus vouchers therapy, and vouchers only; a Relapse and Lapse study; and a CYT Adolescent Study of Abstinence at Discharge. The presentation also addressed implications for future studies and treatment.

The Endogenous Cannabinoids and the Control of Drug Craving
Presenter: Billy R. Martin, Ph.D. (CDD Director: Alexandros Makriyannis, Ph.D.)

SUMMARY: Dr. Billy Martin reviewed new information regarding the regulation of drug craving by CB1 receptors activated by endocannabinoids, as well as the broader role of this regulation in the control of rewarding mechanisms in the brain. Martin speculated as to whether our understanding of the endocannabinoid system can be used to design treatments for substance abuse and other psychiatric disorders.