- Cannabis is the most widely consumed illegal drug in the UK[i]
- 3-4 cannabis cigarettes a day are associated with the same evidence of acute and chronic bronchitis and the same degree of damage to the bronchial mucus membrane as 20 or more tobacco cigarettes a day[ii]
- Cannabis tends to be smoked in a way which increases the puff volume by two-thirds and the depth of inhalation by one-third. There is an average fourfold longer breath-holding time with cannabis than with tobacco[iii]. This means that there is a greater respiratory burden of carbon monoxide and smoke particulates than when smoking a similar quantity of tobacco
- The tar in a cannabis cigarette contains many of the same known carcinogens as tobacco smoke but the concentrations of these are up to 50% higher in the smoke of a cannabis cigarette[iv]
- It also deposits four times as much tar on the respiratory tract as an unfiltered cigarette of the same weight[v]. Smokers of cannabis and tobacco have shown a greater increase in cellular abnormalities indicating a cumulative effect of smoking both[vi]
- In 2001/02, the most commonly used drug by young people was cannabis, which had been used by 33 per cent of young men and 21 per cent of young women in the previous year[vii]
- 44% of 16 to 29 year-olds have tried cannabis at some point in their lives[viii]
- In 2001/02 there were 4.6 million 16 to 59-year-olds living in London. Among this population the British Crime Survey estimates prevalence of illicit drug use was 14 per cent for cannabis[ix]
Impact of cannabis smoking
- It is difficult to ascertain whether or not the inhalation of cannabis smoke causes damage to the lungs and airways independently of the tobacco smoke or not. In general, the studies indicate that there is an increased negative health impact on those who do not smoke cannabis compared to those who do not smoke at all
- When cannabis is smoked with tobacco, the effects are cumulative. However, what is not clear is whether it is the addition of cannabis or the tobacco which is more harmful or whether this is the result of the combined effect of equally harmful substances
- Studies comparing the clinical effects of habitual cannabis smokers versus non-smokers demonstrate a significantly higher prevalence of chronic and acute respiratory symptoms such as chronic cough and sputum production, wheeze and acute bronchitis episodes[x]
- Cannabis smoking is likely to weaken the immune system. Infections of the lung are due to a combination of smoking-related damage to the cells lining the bronchial passage (the fine hair-like projection on these cells filter out inhaled micro-organisms) and impairment of the principal immune cells in the small air sacs caused by cannabis[xi]
- The evidence concerning a possible link between cannabis smoking and COPD has not yet been conclusively established. A number of studies indicate a causal relationship between the two, whereas others contradict these findings[xii]
- The THC in cannabis has been shown to have a bronchodilator effect. This has led to suggestions that THC may have therapeutic benefits in asthma. However, the noxious gases, chronic airway irritation or malignancy after long term use associated with smoking would seem to negate these benefits[xiii]
[i] Annual report on the UK drug situation in 2001, European Monitoring Centre for Drugs and Drug Addiction; Drug Scope, London
[ii] Ashton, H. (2001), Pharmacology and effects of cannabis: a brief review, the Br J of Psychiatry, 178, 101-106
[iii] Wu, TC., Tashkin, DP., Djahed, B. and Rose JE., (1988) Pulmonary Hazards of smoking marijuana as compared with tobacco, New England J of Medicine, 318, 6, 347-351
[iv] Hoffmann, D., Brunnemann, DK., Gori, GB. and Wynder, EL. (1975), On the carcinogenicity of marijuana smoke, Recent Advances in Phytochemistry, 9, 63-81
[v] A Smoking Gun? (2002) British Lung Foundation
[vi] A Smoking Gun? (2002) British Lung Foundation
[vii] National Statistics www.statistics.gov.uk
[viii] http://www.bbc.co.uk/science/hottopics/cannabis/index.shtml
[ix] Written answer to parliamentary question by Caroline Flint MP to Simon Hughes MP 18-03-04
[x] A Smoking Gun? (2002) British Lung Foundation – several studies cited
[xi] Newton, CA., Klein, TW. And Friedman, H. (1994) Secondary immunity to Legionella pneumophila and Th1 activity are suppressed by 9-tetrahydrocannabinol injection, Infect. Immun. 62, 4015-4020
[xii] A Smoking Gun? (2002) British Lung Foundation
[xiii] A Smoking Gun? (2002) British Lung Foundation
