Marijuana Lung Health Report: Less Than Meets the Eye?

On or around November 12 the British Lung Foundation made news in England, the U.S., and probably around the world by releasing a report implying that marijuana smoke is more harmful than tobacco smoke in causing lung and other cancers and infections. The report, nine pages of text plus 90 references, is available at

We found the "shocking new report" (quote from the British Lung Foundation Web site) more interesting for what did not make the news than for what did:

  • This report was based on no new information -- only a re-telling of what was already published. It could have been produced and released at any time. (We could not find any date on the paper, incidentally, except for a 2002 copyright notice on the picture of a marijuana leaf. The press release accompanying the report on the Web was also undated, as of November 18.)

  • No one signed this report -- which seems to have been put together in a hurry, judging by an obvious misspelling ("wieght," page 2, on the Web as of November 18, a week after the story went out to the world) and examples of poor editing which sometimes leave the meaning unclear. Without authors, it is hard to follow up on how the sometimes-incomplete science became headline-making assertions.

  • One question involves the interpretation of the fact that today's marijuana has more of the psychoactive ingredient THC than marijuana in the 1960s and 1970s. The BLF's report carefully says that as a result, "studies investigating the long-term effects of smoking cannabis have to be interpreted cautiously."

    No one could object to careful interpretation of studies. But the public will assume that a higher concentration of THC makes the product more dangerous. We suspect the opposite -- that more THC in marijuana reduces the danger, since many people smoke until they get the effect they want, then stop. If they are going to get the same amount of THC anyway, a higher THC concentration would result in less of the smoke and tar brought into the lungs with it.

    In that case, it is hard to see how the higher concentration today would invalidate earlier studies that did not show long-term harm.

    Also, while everyone agrees that today's marijuana is more potent than that of the 1960s, some dispute the estimate quoted in this report that it has 15 times the THC content. They say this figure was based on a small number of poorly stored samples, which may have deteriorated during storage.

  • We do not know if the report's statement that three or four marijuana cigarettes are as harmful as 20 or more tobacco cigarettes takes account of the fact that marijuana cigarettes are often much thinner -- and that marijuana smokers are likely to smoke much less by weight than tobacco smokers. And many medical marijuana users find relief from just a small puff or two, and have no desire to use more.

  • Other inferences presented in the BLF report also need a closer look. For example, is it reasonable to suggest "an association between cannabis use and opportunistic bacterial and fungal pneumonias" in HIV patients, based on a single reference to a 1985 publication on risk factors in patients referred for possible AIDS care? Is it accurate to highlight cancer risk in one of the two major recommendations of the report, when there is no conclusive evidence that marijuana causes cancer in humans, only laboratory data suggesting that marijuana smoke may do so (U.S. Institute of Medicine report, 1999, p. 119 -- see "For More Information" below)?

  • These concerns just scratch the surface. Others will need to go through the 90 references to see if they are cited in an unbiased fashion, or used to support preconceived conclusions.


Until proven otherwise we will assume that all smoke is unhealthy (even from incense or campfires); it is a matter of degree. With marijuana, vaporizers that heat the substance to a controlled temperature but do not burn it have proven acceptable to users. They may largely eliminate the hazard of inhaling smoke.

On a different issue, the drug war is harmful. In the U.S., marijuana laws have contributed to a huge increase in the prison population, with vast racial disparities. Recently the U.S. attorney general has singled out legitimate medical use of marijuana for special law-enforcement attention and abuse.

A recent Time Magazine cover story on marijuana (November 4, 2002) reported that most Americans do not want marijuana legalized, but do not want users to go to jail either. Public fear of legalization is understandable, if it could bring high-powered corporate promotions, as with tobacco -- including campaigns to target young people and get customers wherever the companies can. U.S. society needs but does not have a middle ground -- for activities that individual adults can do personally without breaking the law, yet which are officially discouraged and cannot be commercially promoted. Such a middle ground will become increasingly necessary as technology progresses, so we should be thinking about it now.

The BLF paper on marijuana is not a scientific or medical review but a political document -- a fact the press largely overlooked. It appears to have been rushed into print now in order to counter recent efforts in the UK and elsewhere to ease the drug war.

For More Information

Understanding Marijuana: A New Look at the Scientific Evidence, by Mitchell Earleywine and G. Alan Marlatt, Oxford University Press, published August, 2002.

Marijuana as Medicine: The Science Beyond the Controversy, by Alison Mack and Janet E. Joy, National Academy Press, published January 2001. This book explains the findings of the 1999 study of medical marijuana by the U.S. Institute of Medicine (Marijuana as Medicine: Assessing the Science Base).

You can read and search this book (or the IOM study) online without charge, at (search titles for "marijuana"). The study is also online in a different format at:

For Web sites on medical marijuana, we found that searching for "medical marijuana" worked well. Be aware that Google sells ads that may appear with search results -- but they are marked as sponsored links, and do not appear beyond the first three positions.

[Note: OK to distribute this article if it is reproduced unchanged -- including this notice with the publication date (November 22, 2002) and our contact information (]

ISSN # 1052-4207

Copyright 2002 by John S. James. Permission granted for noncommercial reproduction, provided that our address and phone number are included if more than short quotations are used.