Respiratory Diseases

Respiratory Diseases are often cited as the major health threat of smoked marijuana. Some studies have attempted to prove that marijuana smoke contains carcinogenic materials and leads to lung damage as does tobacco smoke. [1] Such research often fails to provide adequate controls, as in a 1972 study of US servicemen who smoked hashish and tobacco. A review of the published data reveals that not a single case of lung cancer has ever been attributed to marijuana smoke. [2]

Comparing tobacco smoking to marijuana smoking only reveals that marijuana smoke is relatively harmless. As has been noted by the National Academy of Sciences, 50 to 60 million American tobacco smokers produce about 150,000 cases of lung cancer per year. If marijuana smoking were equally dangerous, than the estimated 10 to 15 million current marijuana smokers in America should produce in the range of 30 to 40 thousand lung cancer cases, but again, not even one such case has been reported. [3]

The argument that cannabis smoke may be as hazardous as tobacco smoke is weakened by the disparity in quantity of material smoked and also by the lack of epidemiological evidence. A patient suffering from a chronic condition might inhale in the range of three grams of medicinal marijuana per day. [4] [5] Comparatively, the typical tobacco addict who smokes twenty or more cigarettes per day consumes about four to five times that amount of plant material. The actual amount of smoke produced is in the range of seven times greater for cigarette smokers than for heavy marijuana smokers. [6] While it usually takes a chronic tobacco addict twenty years to develop lung cancer, it would take a marijuana smoker at least eighty years of constant chronic use to develop lung cancer, if cannabis smoke were as dangerous as tobacco. [7]

Any comparisons between cannabis and tobacco are seriously flawed in that the respiratory effects of the two materials are distinctly different. Cannabis smoke is known to be a bronchial dilator that helps clear the larger central airways of the lung, while tobacco smoke is known penetrate the lung’s smaller peripheral air passages, causing blockages and leading to emphysema. [8] Donald Tashkin, a federally sponsored leading pulminologist with the UCLA, has conducted what UCSF researcher Abrams called “elegant” research indicating that cannabinoids actually protect human lungs from diseased conditions such as emphysema. [9] [10] In 1994, Tashkin lectured on his study of habitual marijuana smokers. He concluded that marijuana smokers do not face the same degree of lung injury as tobacco addicts. Tashkin cited two main reasons; First, in the population he studied, tobacco smokers inhaled an average of 25 cigarettes per day, compated to heavy marijuana users who smoked an average of three or four marijuana “joints” per day—a sevenfold difference in the amount of smoke inhaled. Second, there is a qualitative difference between tobacco and marijuana smoke. Extensive testing determined that marijuana smoke does not precipitate the same destructive changes to lung tissue as does tobacco smoke. Marijuana and tobacco smoke may both contain toxic compounds; however, unlike cannabis, tobacco smoke causes inflammation of the lung’s absorbent macrophages. This evidence led Dr. Tashkin to theorize that marijuana smoke may actually release compounds known to suppress inflammation of the lung’s macrophages, thereby blocking the absorption of toxic substances. [11]

Whereas marijuana in medical use is often criticized because it is known to contain about 421 interrelated compounds, tobacco cigarettes contain more than 4,000 ingredients. [12] More than a half million Americans per year die from tobacco-related illnesses, but not one death has ever been attributed to smoking cannabis. In 1990, the 20th edition of the California Research Advisory Panel annual report declared that, “An objective consideration of marijuana shows that it is responsible for less damage to society and the individual than are alcohol and cigarettes. [13] In 1997, the United Nations World Health Organization published an identical declaration. Unfortunately, public release of that comprehensive report was suppressed in the United States. [14]

A survey by the Kaiser Permanente Center found that marijuana-only smokers have a 19% higher rate of respiratory complaints than nonsmokers. [15] An early paper by Donald Tashkin reported evidence of minor lung damage caused by frequent marijuana smoking. [16] In the US government’s 1999 review of scientific literature, the Institute of Medicine considered these and similar published reports. In assessing this aspect of medical marijuana, and IOM Executive Summary notes that, “Numerous studies suggest that marijuana smoke is an important risk factor in the development of respiratory disease.” [17] Yet the IOM report apparently failed to consider a number of recent studies that clearly contradict the assertion that marijuana smoke is a risk factor for respiratory disease. Harvard Medical Professor Lester Grinspoon, M.D., states that the IOM report “greatly exaggerated” the risks of smoking marijuana. [18] Many other physicians and medical researchers have reported that even long-term inhalation of marijuana smoke does not cause any type of lung disease.

A 1992 paper studied the effects of cannabis on ventilatory drive and metabolic rate in eleven young, healthy, marijuana-only smoking men. There was no evidence of hypercapnia (increased carbon dioxide to the blood) or hypoxia (lowered oxygen in the blood). To quote the study, “We conclude that smoking marijuana (13 to 27 mg THC) has no acute effect on central or peripheral venilatory drive or metabolic rate in habitual marijuana smokers.” [19] Also in 1992, the National Academy of Science reported a similar finding: “Other than brochiodilation, it has proven difficult to demonstrate any effects of acute cannabis smoking on breathing as measured by conventional pulmonary [respiratory] testing.” [20]

In 1997, a UCLA team headed by Tashkin concluded an extensive study of 394 participents. Comprehensive analysis found that habitual long-term marijuana smokers do not experience a greater decline in lung function than nonsmokers. Researchers remared, “Neither the continuing nor the intermittent marijuana smokers exhibited any significantly different rates of decline in [lung function]. No differences were noted between even quite heavy marijuana smoking and nonsmoking of marijuana.” In contrast, the tobacco-only smokers in the study experienced a rapid decline in lung function during the eight years of pulmonary examination. The study also found no connection between marijuana and tobacco in those who smoked both. The evidence from this exhaustive, real-world study indicates that the pulmonary health of marijuana smokers is no different from that of the general population. [21]

A 1995 editorial in The Lancet, the premier medical journal in Britain, opened with this definitive assessment: “The smoking of cannabis, even long term, is not harmful to health.” [22] The respected UK medical authority published a more thorough analysis of marijuana’s harmful effects in 1998. Editors of The Lancet concluded that, “moderate indulgence in cannabis has little ill effect.” [23] These findings are similar to those presented by the United Nations World Heath Organization in 1997 in the report that was officially suppressed in the United States. [24]

US Drug Czars refuse to recognize accepted medical research and instead cite questionable government studies showing that cannabis smoke contains carcinogens and therefore must cause lung cancer. [25] Their assertions make effective media “sound bites,” but lose their power upon exposure to the facts. It is well known that marijuana available for study from the National Institute on Drug Abuse (NIDA) is not satisfactory for medical use. Researchers and patients receiving cannabis grown by the federal government have learned to remove a large percentage of unsmokable plant materials—seeds, stems, and unknown substances—prior to smoking or eating. [26] [27] It is doubtful that researchers cleaned the inferior government-grown marijuana before burning it to identify smoke by-products in anti-marijuana studies funded by NIDA. Even granting consideration to the questionable data touted by Drug Czars, the 1999 Institute of Medicine report was cautious to qualify its judgement on the potential risk for lung damage. Discrediting alarmist propaganda, the IOM report concluded, “… proof that habitual marijuana smoking does or does not cause cancer awaits the results of well-designed studies.” [28]

Unfortunately, federal censorship prevented the IOM investigators from assessing the implications of the suppressed National Toxicology Program study referred to in the Cancer section of this book. [29] That study supports the claims of cancer survivors who attribute some aspect of their remission to continued use of medical marijuana.

In reviewing pulmonary hazards associated with marijuana smoke, the mode of administration is a critical factor that is frequently ignored. It is important to note the recent development of vaporizer technology. Because the ignition temperature of THC is much lower than that required to ignite plant material, modern vaporizers offer a potentially safer method of inhaled administration. However, this health-conscious technology is severely restricted by “drug paraphernalia” ordinances prohibiting sale and promotion of illegal merchandise. As with prohibition of needle-exchange programs for IV drug users, the illegal status of the drug only contributes to its potential harm.

Another significant factor in assessing pulmonary hazards is the strength of the marijuana. The 1987 edition of the Merck manual of pharmaceutical drugs stated that marijuana used in the United States does in fact have higher THC content than in former years. Critics have incorporated this observation into warnings, but the fact is that the health risks of smoking cannabis are lower with the higher-potency marijuana available today than they were back when people were smoking a relatively inferior grade. Low-potency marijuana requires much greater consumption and certainly increases any potential respiratory health risks. Marijuana leaf, or “shake,” is usually of minimal potency and burns hotter than the dense flowering tops, frequently causing coughing fits upon deep inhalation.

Marijuana used for clinical research in assessing the risk of associated lung damage is notoriously inferior to cannabis obtained through medical marijuana groups or the black market. Marijuana supplied by the National Institute on Drug Abuse is only about 25% as potent as average grades of medical cannabis used, for example, in San Francisco Bay Area medical cannabis clubs. The Institute of Medicine report of 1999 cites the risk of smoking as the one notable health hazard of cannabis consumption, yet patients receiving cannabis grown by the government through research studies and through the Compassionate Use Investigational New Drugs Program face four to five times greater exposure to potential smoke hazards than do the many thousands of patients who procure their medicine through illegal cannabis dispensaries. [30]

Related sections: Cancer, Immune Responses, Smoking Methods, Upper Respiratory Infection.


[1] Ungerleider and Andrysiak, “Bias and the Cannabis researcher.” Journal of Clinical Pharmacology (8-9 Suppl) pp. 153S-158S, August 21, 1981

[2] Nelson, “A critical review of the research literature concerning some biological and psychological effects of cannabis.” Advisory Committee on Illicit Drugs, Cannabis and the Law in Queensland: Criminal Justice Commission of Queensland, Australia, 1993

[3] Edwards, M.D., Testimony before the National Academy of Sciences in New Orleans, January 1998

[4] Mikuriya, Testimony during a medical necessity trial in the State of Washington, December, 1996

[5] Abrams, Lindesmith Center Lecture, San Francisco, May 17, 1999

[6] Gagnon, “Marijuana Less Harmful to Lungs than Cigarettes.” Medical Post (Quebec), September 6, 1994

[7] Edwards, M.D., op. cit.

[8] Tashkin, et al., “Effects of habitual use of marijuana and/or cocaine on the lung.” Research Findings on Smoking of Abused Substances, NIDA Research Monograph 99, 1990

[9] Abrams, op. cit.

[10] Gagnon, op. cit.

[11] Ibid.

[12] Partnership for a Drug Free America, public information television release, May 1998

[13] California Research Advisory Panel, 1990

[14] James, “Medical marijuana: Unpublished federal study found THC treated rats lived longer, had fewer cancers.” AIDS Treatment News, January 17, 1997

[15] “Health care use by frequent marijuana smokers who do not smoke tobacco.” Western Journal of Medicine, Vol. 158, No. 6, pp. 596-601, June, 1993

[16] Tashkin, “Is frequent marijuana smoking hazardous to health?” Western Journal of Medicine, Vol. 158, No. 6, pp. 635-637, June, 1993

[17] Institute of Medicine, Marijuana and Medicine: Assessing the Science Base. Washington, DC: National Academy Press, 1999

[18] Wishnia, “The IOM Medical-Marijuana Report.” High Times, July 1999

[19] Wu, Wright, Sassoon, and Tashkin, “Effects of smoked marijuana on varying potency on ventilatory drive and metabolic rate.” American Review of Respiratory Disease, Vo. 146, No. 3, pp. 716-721, 1992

[20] US National Academy of Science quoted in, “The health and psychological consequences of cannabis use.” Chapter 6, National Drug Strategy Monograph No. 25, Australia

[21] “Heavy long-term marijuana use does not impair lung function, says new study. Los Angeles Times, May 3, 1997

[22] “Deglamorizing cannabis.” Editorial, The Lancet, Vol. 346, No. 8985, p. 1241, November 11, 1995

[23] Schlosser, “The Politics of Pot: A Government in Denial.” Rolling Stone, March 4, 1999

[24] Radford (Science Editor), “UN Study Suppressed.” The San Francisco Guardian, February 19, 1998

[25] Medical Marijuana on Town Meeting, KOMO TV, Seattle, March 9, 1997

[26] Abrams, Lindesmith Center Lecture, San Francisco, May 17, 1999

[27] Conversations with Elvy Musikka, federally authorized medical marijuana patient, 1997-1999

[28] Institute of Medicine, Marijuana and Medicine: Assessing the Science Base. Washington, DC: National Academy Press, 1999

[29] Abrams, op. cit.

[30] “Lab tests show cannabis clubs’ medical marijuana superior to government’s.” Press Release, CANORML, May 21, 1999, Source: