A few clarifications about this study: 1. No rats were exposed to marijuana, as incorrectly stated in this summary. Rather, they were exposed to a potent, synthetic CB1 agonists, WIN55,212-2. 2. No "permanent" changes were documented. Subjects were tested 20 days following daily exposure, so a correct assessment would be to note that changes were noted up to three weeks following exposure. 3. Investigators noted no changes in behavior or serotonin levels in non-adolescent rats. 4. This data is far from conclusive. In fact, a previous trial involving rats and cannabinoid agonists found that exposure was associated with just the opposite result -- in that case, neurogenesis. See: New Scientist, October 13, 2005 -- ���A synthetic chemical similar to the active ingredient in marijuana makes new cells grow in rat brains. What is more, in rats this cell growth appears to be linked with reducing anxiety and depression.���

The sumary reflects the reporting in the Canadian Press, which referred to "cannabis exposure" and quoted the study author as concluding that her research found "permanent changes in the brain." However, Paul is correct that a reading of the abstract reveals that the researcher used a synthetic cannabinoid agonist rather than exposing the lab rats to marijuana or marijuana smoke. We encourage readers to click through to the original journal article for a more thorough reading of the study methods and conclusions.

The conclusions of this research would not surprise me at all. I find it disturbing when I read the comments in JoinTogether from advocates of recreational and medical marijuana immediately trying to denigrate any new finding on neurologic and other impacts of marijuana. Caring people should be concerned about the possible health impacts of commonly used substances -- if not for themselves then at least for other people. Personal beliefs about marijuana use should be trumped by public health concerns. The science on marijuana impact continues to unfold and it should guide public policy. Personal wishes about individual marijuana use should not affect public policy.

This misrepresentation of the study by the media, but more shockingly by the study author demonstrates the lack of candor and hard investigative reporting when it comes to the issue of marijuana. Though JT responded by indicating that the misrepresentation "problem" came from the Canadian press, it is still incumbent upon those seeking truth (and I include the editors at JT in this) to fact-check diligently.

I smoked marijuana daily at 17 years old and have felt different ever since stopping that, I ended up having more difficulty relaxing, sleeping, and finding energy than I did before daily marijuana use. Today I take amino acids that increase the amount of serotonin and norepinephrine, and it makes me feel normal again. It's true that my one case doesn't necessarily prove or disprove anything about marijuana, but I find it funny that there are people who immediately dismiss evidence of marijuana's harmful affects while immediately claiming that marijuana is harmless, as if the brain is so easy to figure out that they already know everything there is to know about marijuana's affects on the brain.

For additional information and perspectives on the harmfulness of marijuana, see http://gordondrugabuseprevention.com and http://spiritualharmofmarijuana.com It is interesting to note that there are references to work on both website that speak about the long term effects of marijuana use.

Very hard to judge the dose of the synthetic cannabinoid used in the study relative to the amount of THC obtained by inhaling marijuana smoke. In addition, they used a once daily intraperitoneal injection that typically yields a rapid high concentration in the brain and then rapid re-distribution. My work and that of others has shown that early adolescent exposure of rats to nicotine produces changes in the young adult rat that includes enhanced responding for or reward from nicotine, cocaine and diazepam. In sum, best that the still developing brain of young adolescents not be exposed to chemicals that alter neuronal function.

"The science on marijuana impact continues to unfold and it should guide public policy." I agree -- which is why I made it a point to read the full text of the study itself, not just the news summaries or the abstract -- and clarified the points that had either been misreported or not reported at all. There was no opinion in my post, simply clarifications based on what the study actually said.

JBrennan reports having "smoked marijuana at 17 years old", but saw fit to stop. The relevance of his experience is no more obvious than that of administering some amount of synthetic cannabinoid to rats, because he does not specify whether the daily dosage was a single toke or one or more 500-mg. hot-burning overdose paperjoints loaded with "confounding factors" such as heat shock and carbon monoxide. This traditional ignoring of dosage technology issues voids the validity of most discussions of cannabis safety.

If memory serves correct, the criteria for generalizing a study is a minimum of 270 (human) participants--Not an observation of 18 teen lab rats. The famous Nixon commission on marijuana ('70-'72) reached the unexpected conclusion: "marijuana should be decriminalized under State & Federal levels...Considering the range of social concerns in contemporary America, marijuana does not rank very high." A META-analysis of marijuana studies confirms that, "the physical & mental health risks of smoking a marijuana cigarette a day are equal to that of drinking a cup of coffee a day." Perhaps based on Gobbi's research, we may conclude that a cup of coffee a day causes permanent brain damage?? ;P...