BLF Claims Cannabis Causes Cancer

Published June 29, 2012



British Lung Foundation Claims Cannabis Causes Cancer


Contrary to the growing body of evidence that smoked THC not only doesn’t cause cancer but potentially has anti cancer properties the British Lung Foundation (BLF) released a report in 2012 stating that, among other things,  “88% (of cannabis smokers) incorrectly thought tobacco cigarettes were more harmful than cannabis ones – when the risk of lung cancer is actually 20 times higher.”


This hyperbole was then amplified through UK media via the BBC News with:



Experts are warning that the public dangerously underestimates the health risks linked to smoking cannabis.

The British Lung Foundation carried out a survey of 1,000 adults and found a third wrongly believed cannabis did not harm health.

And 88% incorrectly thought tobacco cigarettes were more harmful than cannabis ones – when the risk of lung cancer is actually 20 times higher.

The BLF said the lack of awareness was “alarming”.

Widely used

Latest figures show that 30% of 16-59 year-olds in England and Wales have used cannabis in their lifetimes.

A new report from the BLF says there are established scientific links between smoking cannabis and tuberculosis, acute bronchitis and lung cancer.

Part of the reason for this, say the experts, is that people smoking cannabis take deeper puffs and hold them for longer than when smoking tobacco cigarettes.

“This is not a niche problem.” Dame Helena Shovelton British Lung Foundation said.  This means that someone smoking a cannabis cigarette inhales four times as much tar as from a tobacco cigarette, and five times as much carbon monoxide, the BLF says. Its survey found that young people are particularly unaware of the risks.  Some studies have also suggested cannabis increases the chances of developing mental health problems such as schizophrenia.

Almost 40% of the under-35s surveyed – the age group most likely to have smoked it – thought cannabis was not harmful.

However, the BLF report warned that smoking one cannabis cigarette every day for a year increases the chances of developing lung cancer by a similar amount as smoking 20 tobacco cigarettes each day for one year.”


From BBC News health:


[End Quote]

While the Independent headlined with this,


“Young cannabis users ‘do not realise the huge danger to their health”


And the Daily Mail led out with,


“Cannabis rule means children face ‘cancer time bomb’”


Sensational stuff, but let’s look at the facts…


Surveys, with their appearance of objectivity, are a popular way for groups, commercial or otherwise, to win press attention. It has worked for the BLF before – the Daily Mail has a ten-year old article archived online reporting a virtually identical story of BLF “research” released in 2002 titled “A Smoking Gun” that compared the health risks of smoking tobacco to cannabis. Putting aside the tabloid like “A Smoking Gun” title, rather than introducing new scientific data to their latest study, the authors simply selectively cherry picked studies already conducted over the years that supported their notably biased stance, disregarding a growing body of research/evidence that demonstrates that smoked cannabis does not cause cancer, respiratory disease, and/or pulmonary disorders. In fact, based on recent research smoked cannabis may even have a “protective” effect against cancer – the BLF, of course, failing to cite this research. 


As Professor David Nutt, the onetime key advisor to the UK Government on Drug Policy (ACMD) notes on his blog (June 11, 2012):



“The BLF’s report itself references a great deal of scientific evidence, but it seems to be an attempt to collect evidence that supports their predetermined opinion that cannabis harms the lungs, rather than exploring the evidence to find out what the balance of findings really suggests. When the evidence they found was mixed, they came to firm conclusions that the most alarming interpretation of the most alarming evidence was true. This is most striking in the case of the lung cancer claim that tops the press release, that a cannabis joint is 20 times as carcinogenic as a cigarette. This is an old chestnut, listed amongst Wikipedia’s list of popular drug myths but that didn’t stop Kenneth Gibson of the Scottish National Party lodging a motion (look for S4M-03197) in the Scottish Parliament last week on 8th June endorsing the BLF’s claims and recommendations.”


[End Quote]

Read Prof David Nutt’s blog

The data for their paper appears to be taken mainly from two papers published in 1987, Tashkin, DP, Coulson, AH, Clark, VA, et al and Gong, H, Fligiel, S, Tashkin, DP, Barbers, RG, but these papers themselves did not make the explicit claim and did not make any numerical link between joints and cigarettes. Rather the BLF decided to distort the research, ignore other significant research that countered their own stance and present their own more severe conclusion to the press. As this was reported and exaggerated by the media, and other papers cited the BLF, the myth has spread without anyone bothering to analyze the source material.


In fact, had the media even vaguely scratched the surface they would have found Taskin’s 2006 study unexpectedly concluded that smoking marijuana, even regularly and heavily, does not lead to lung cancer, and there was even a suggestion of some “protective effect” among marijuana smokers who had lower incidences of cancer compared to non-users. The study followed 5,115 regular pot smokers over the course of 20 years.

Tashkin’s group at the David Geffen School of Medicine at UCLA had hypothesized that marijuana would raise the risk of cancer on the basis of earlier small human studies, lab studies of animals, and the fact that marijuana users inhale more deeply and generally hold smoke in their lungs longer than tobacco smokers — exposing them to the dangerous chemicals for a longer time.

While no association between marijuana smoking and cancer was found, the study findings, presented to the American Thoracic Society International Conference, did find a 20-fold increase in lung cancer among people who smoked two or more packs of cigarettes a day.


U.S. Federal health and drug enforcement officials have widely used Tashkin’s previous work on marijuana to make the case that the drug is dangerous. Tashkin said that while he still believes marijuana is potentially harmful, its cancer-causing effects appear to be of less concern than previously thought. (Source the Washington Post. Friday, May 26, 2006, By Marc Kaufman)


Tashkin is backed up by an earlier 1997 study by researchers at the Kaiser-Permanente HMO. They monitored nearly 65,000 patients for nearly a decade, comparing cancer rates among non-smokers, tobacco smokers, and marijuana smokers. Tobacco smokers had massively higher rates of lung cancer and other cancers. Marijuana smokers who didn’t also use tobacco had no increase in cancer risk, and in fact their rates of lung and most other cancers were slightly lower than non-smokers. (Sidney S, Quesenberry CP Jr, Friedman GD, Tekawa IS (1997) Marijuana use and cancer incidence (California, United States)


While a 2012 study conducted by Mark J. Pletcher et al concludes:



“In this 20-year study of marijuana and pulmonary function, we confirmed the expected reductions in FEV1 and FVC from tobacco use. In contrast, marijuana use was associated with higher FEV1 and FVC at the low levels of exposure typical for most marijuana users. With up to 7 joint-years of lifetime exposure (eg, 1 joint/d for 7 years or 1 joint/wk for 49 years), we found no evidence that increasing exposure to marijuana adversely affects pulmonary function.”

[End Quote]

Read study here… 


But, let’s go back even further. 


The first important research that demonstrated THC could retard cancer in mice was published in 1975. This was a study conducted by the Journal of the National Cancer Institute in and funded and supported by the American Cancer Society, NIDA, and other grants.


It notes:




Lewis lung adenocarcinoma growth was retarded by the oral administration of delta-9-tetrahydrocannabinol, delta-8-tetrahydrocannabinol, and cannabinol (CBN), but not cannabidiol (CBD). Animals treated for 10 consecutive days with delta-9-THC, beginning the day after tumor implantation, demonstrated a dose- dependent action of retarded tumor growth. Mice treated for 20 consecutive days with delta-8-THC and CBN had reduced primary tumor size. CBD showed no inhibitory effect on tumor growth at 14, 21, or 28 days. Delta-9-THC, delta-8-THC, and CBN increased the mean survival time (36% at 100 mg/kg, 25% at 200 mg/kg, and 27% at 50 mg/kg;, respectively), whereas CBD did not. Delta-9-THC administered orally daily until death in doses of 50, 100, or 200 mg/kg did not increase the life-spans of (C57BL/6 X DBA/2) F (BDF) mice hosting the L1210 murine leukemia. However, delta-9-THC administered daily for 10 days significantly inhibited leukemia virus-induced splenomegaly by 71% at 200 mg/kg as compared to 90.2% for actinomycin D. Experiments with bone marrow and isolated Lewis lung cells incubated in vitro with delta-8-THC and delta-9-THC showed a dose-dependent (10 -4 10 -7) inhibition (80-20%, respectively) of tritiated thymidine and 14C -uridine uptake into these cells. CBD was active only in high concentrations (10 -4)


The research concluding:


“These results lend further support to increasing evidence that, in addition to the well-known behavioral effects of delta-9-THC, this agent modifies other cell responses that may have greater biologic significance in that they have antineoplastic activity. The high doses of delta-9-THC (i.e., 200 mg/kg) are not tolerable in humans. On a body-surface basis, this would be about 17 mg/m(2) for mice. Extrapolation to a 60-kg man would require 1,020 mg for comparable dosage. The highest doses administered to man have been 250-300 mg (14). Whether only cannabinoids active in the central nervous system (CNS) exhibit this antineoplastic property is not the question, since CBN, which lacks marihuana-like psychoactivity, is quite active in our systems (15).

With structure-activity investigations, more active agents may be designed and synthesized which are devoid of or have reduced CNS activity. That these compounds readily cross the blood-brain barrier and do not possess many of the toxic manifestations of presently used cytotoxic agents, makes them an appealing group of drugs to study. 1


[End Quote]

Read full paper here.  

According to author Jack Herer, the DEA subsequently shut down the study and all further cannabis/tumor research. As a result, in 1976 President Gerald Ford put an end to all public cannabis research and granted exclusive research rights to major pharmaceutical companies, who set out, unsuccessfully, to develop synthetic THC that would deliver shown medical benefits without the high. In 1983 the Reagan/Bush Administration tried to persuade American universities and researchers to destroy all 1966-76 cannabis research work, including compendiums in libraries. Jack Herer is quoted with, “We know that large amounts of information have since disappeared.”


Shoot forward over 25 years…


Madrid Research (2000) Backs 1975 Findings

In February 2000 researchers in Madrid announced they had destroyed incurable brain tumors in rats by injecting them with THC, the active ingredient in cannabis.

The Madrid study marks only the second time that THC has been administered to tumor-bearing animals; the first was a Virginia investigation 26 years ago. In both studies, the THC shrank or destroyed tumors in a majority of the test subjects.

Most Americans don’t know anything about the Madrid discovery. Not surprisingly, virtually no major U.S. newspapers carried the story, which ran only once on the AP and UPI news wires, on Feb. 29, 2000. The New York Times, Washington Post and Los Angeles Times all ignored the story, even though its newsworthiness is indisputable: a benign substance occurring in nature destroys deadly brain tumors.


The Madrid researchers reported in the March issue of “Nature Medicine” that they injected the brains of 45 rats with cancer cells, producing tumors whose presence they confirmed through magnetic resonance imaging (MRI). On the 12th day they injected 15 of the rats with THC and 15 with Win-55,212-2 a synthetic compound similar to THC. “All the rats left untreated uniformly died 12-18 days after glioma (brain cancer) cell inoculation … Cannabinoid (THC)-treated rats survived significantly longer than control rats. THC administration was ineffective in three rats, which died by days 16-18. Nine of the THC-treated rats surpassed the time of death of untreated rats, and survived up to 19-35 days. Moreover, the tumor was completely eradicated in three of the treated rats.” The rats treated with Win-55,212-2 showed similar results.

The Spanish researchers, led by Dr. Manuel Guzman of Complutense University, also irrigated healthy rats’ brains with large doses of THC for seven days, to test for harmful biochemical or neurological effects. They found none.2

The BLF Research


The BLF report notes that although cannabis is the world’s most widely used illicit drug, there is surprisingly little research into its effects on lung health, with far less about the effects of cannabis smoke than tobacco smoke. However, it says there is now research showing that the active component, THC, can suppress the immune system and that cannabis smokers may be at risk of:

  • respiratory problems such as chronic coughing, wheezing, sputum production, acute bronchitis, airway obstruction
  • infective lung conditions such as tuberculosis and Legionnaire’s disease
  • pneumothorax (collapsed lung)
  • lung cancer – one study, which was widely quoted in the papers, suggested that smoking just one cannabis cigarette a day for one year increases the risk of developing lung cancer by a similar amount to smoking 20 tobacco cigarettes for the same period. It concluded that 5% of lung cancers in those aged 55 or under may be caused by smoking cannabis.

However, the report points out that there is a lack of conclusive evidence as to the possible effect that smoking cannabis has on lung function and the risk of developing chronic obstructive pulmonary disease (COPD). There is evidence that smoking cannabis with tobacco leads to a greater risk of COPD than smoking tobacco alone.


The claim about the 20-fold cancer risk is prominent in the introductory ‘background’ information section of the BLF’s report. It claims that the evidence explored in the report shows this conclusively. But the report contradicts itself. Section 3.2 on cancer goes onto say that “studies in human populations have yielded conflicting evidence on the subject: some suggest there is a link between smoking cannabis and lung cancer while others don’t. It’s worth noting that these studies are of limited value as they looked at relatively small numbers of people and didn’t take into consideration the quantity of cannabis smoked or the effects of smoking a mixture of tobacco and cannabis – a practice that is common in the UK, Europe, and several other countries. Thus, no comparative data between cancer rates amongst those who smoke cannabis mixed with tobacco and those who smoke cannabis alone is introduced. On this basis alone how can the BLF claim cannabis causes cancer when the vast majority of UK and European cannabis smokers are smoking tobacco with cannabis?


The BLF paper has since been called to task by numerous organizations with calls by some for the BLF to explain their research and the media to print retractions. To date neither has happened.


The obvious question that needs asking is that if the BLF’s claims are true where are all the deaths? A widely cited report by the Independent Drug Monitoring Unit states that there are at least 3 million cannabis smokers in the UK (with some estimates higher and lower), and the general consensus is that there are about 9 million tobacco smokers.

National mortality statistics note that around 100,000 people die each year from illnesses directly linked to smoking cigarettes. 42,800 are from smoking-related cancers, 30,600 from cardiovascular disease and 29,100 die slowly from emphysema and other chronic lung diseases.


So what amount of deaths are linked to smoking cannabis? None! At least for now, this is an irrefutable statistical fact that goes far beyond any politically laden drug war rhetoric.


A Valuable Opportunity Lost – Harm Maximization


In October 2009, the UK Government sacked their chief drug advisor, Professor David Nutt – head of the Advisory Council on the Misuse of Drugs (ACMD). The sacking occurred after Professor Nutt had publicly stated the dangers of alcohol and tobacco were more serious than those posed by Ecstasy and LSD and criticised the decision to reclassify cannabis from a Class C to Class B drug, against ACMD advice.


He accused ministers of devaluing and distorting scientific evidence and described his sacking as a “serious challenge to the value of science in relation to the government”.


Liberal Democrat home affairs spokesman Chris Huhne said the decision to sack the adviser was “disgraceful”.


“What is the point of having independent scientific advice if as soon as you get some advice that you don’t like, you sack the person who has given it to you?” He added, that if the government did not want to take expert scientific advice, it might as well have “a committee of tabloid newspaper editors to advise on drugs policy”.


By November 2009, five more scientists would quit the Advisory Council on the Misuse of Drugs.


According to the most recent and well-regarded UK study on the physical damage drugs can cause. “Drug harms in the UK: a multi-criteria decision analysis”, a 2009 study from the Independent Scientific Committee on Drugs published in The Lancet (and reported on by multiple media outlets) is very clear about which drugs are most harmful.

The study placed heroin, crack, cocaine, meth, tobacco and alcohol well above marijuana, both in terms of harm to self and harm to others. Alcohol was ranked the most dangerous drug while tobacco ranked above ecstasy and cannabis.


Tobacco causes 40 percent of all UK hospital illnesses, while alcohol is blamed for more than half of all visits to hospital emergency rooms.


Which brings us to our next point. The BLF coincidently has now published two papers on cannabis causing cancer but is yet to publish a single dedicated paper surrounding tobacco and cancer. Tobacco is, after all, the major contributing factor to lung cancer and respiratory diseases. Based on this, it stands to reason that with the majority of Britons mixing tobacco with cannabis the warning bells should have been sounded as to the danger of this practice. I.e. Smoking pure dank is far less harmful than smoking a cannabis/tobacco mix.


Read more about cannabis and cancer here…


Read BLF Paper – “A Smoking Gun”




  1. A.E. Munson, L.S. Harris, M.A. Friedman, W.L. Dewey, and R.A. Carchman (1975) Antineoplastic activity of cannabinoids
  2. Manuel Guzmán (2003) Cannabinoids: potential anticancer agents, in Nature Reviews Cancer 3, 745-755 (October 2003)