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Marijuana Affects Brain Similarly to Opiates and Alcohol, Says Two New Marijuana Studies


July 1997

The effects of marijuana on the brain resemble those of harder drugs such as heroin and cocaine, according to two new studies on marijuana published in the journal Science (G. Tanda, F.E. Pontieri, G.D. Chiara, "Cannabinoid and Heroin Activation of Mesolimbic Dopamine Transmission by a Common µ1 Opioid Receptor Mechanism," Science, June 27, 1997, p. 2048; F. Rodriguez de Foncesca, M.R.A. Carrera, M. Navarro, G.F. Koob, F. Weiss, "Activation of Corticotropin-Releasing Factor in the Limbic System During Cannabinoid Withdrawal," Science, June 27, 1997, p. 2050; I. Wickelgren, "Drug Addiction: Marijuana: Harder Than Thought?" Science, June 27, 1997, p. 1967).

One study, by researchers from the University of Cagliari in Italy, concluded that there may be a relation between "the degree and frequency of Cannabis use and the probability of subsequent heroin self-administration." Although, the researchers note, "our results do not provide direct evidence for a causal relation between Cannabis and heroin use, they are nonetheless consistent with this possibility." This study infused THC into rats and found that the levels of dopamine in their nucleus accumbens doubled, as did the levels when heroin was infused instead.

The other study, conducted by researchers from the Scripps Research Institute in La Jolla, CA and Complutense University in Spain and funded by the National Institute on Drug Abuse, showed that "Cannaboid abuse may lead to a subtle disruption of hedonic systems in the brain that are then `primed' for further disruption by other drugs of abuse." This study traced the symptoms of emotional stress caused by marijuana withdrawal to a peptide that has been linked with anxiety and stress during heroin and cocaine withdrawal.

Friedbert Weiss, an author of the second study, said chronic marijuana use increases the susceptibility of the brain to future drug use. "It becomes a vicious cycle of dependence," he said. George Koob, another author of the study said that the results of his study "blur the distinction between what is considered a hard drug and a soft drug." However, he said, the study's findings do not necessarily argue against the use of marijuana for medical purposes. "I don't think our study in any way undermines the potential therapeutic use of marijuana," he said. "But we can't bury our heads in the sand and say that it doesn't have abuse potential because it does," (Associated Press, "Marijuana leads to harder drugs, researchers say," Washington Times, June 27, 1997, p. A11; Thomas H. Maugh II, "Studies Support View of Marijuana as `Gateway' Drug," Los Angeles Times (Washington Edition), June 27, 1997, p. A1; Curt Suplee, "Marijuana's Effects on Brain Studied," Washington Post, June 27, 1997, p. A10).

Dr. Lester Grinspoon of Harvard University, disagrees with the Italian researchers who contend that because both marijuana and heroin use the same biochemical pathways, marijuana ought to be approached with equivalent caution. "This doesn't prove anything," he said. "To the extent the effects of pot have something to do with the pleasure centers in the brain, it has something in common with heroin or cocaine, But it also has something in common with sex and chocolate."