Is cannabis smoking more harmful than cigarette smoking?

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A study published in the journal, Thorax, recently hit the headlines as demonstrating that smoking a cannabis joint was at least twice as harmful to lung function as smoking a cigarette. So what are the dangers of smoking cannabis and how do these risks compare to those of smoking tobacco?

Firstly, we can’t ignore the fact that in most places and circumstances possession of cannabis is a criminal offence with potentially serious legal consequences and testing positive for cannabis use in the workplace can seriously harm your career. That being said, it is difficult to tease out the health effects of cannabis smoking, partly because almost all cannabis smokers are or have been tobacco smokers as well. The recent study compared lung effects on four groups, each consisting of around 80 volunteers: 1. Cannabis users (at least a joint a day for 5 years), 2. Cigarettes only smokers (at least 20 per day for at least a year), 3. Those who smoke both cigarettes and cannabis and 4. Never smokers. When they scanned the lungs for evidence of emphysema they found that only 1% of the cannabis only users had emphysema, as did 19% of the cigarette smokers, 16% of those using both cigarettes and cannabis and 0% of the never smokers. This appears to show that although cannabis smoking worsens lung function, structural damage is common only with cigarette smoking. This finding likely reflects the different ways in which the products are used. A cannabis joint is typically smoked with greater intensity, with larger puff volumes and breath holding, leading to greater smoke and carbon-monoxide exposure than from a single cigarette (hence the greater impact on lung function on a per-smoke basis). However, while most regular cannabis smokers will smoke less than 5 joints per day, most regular cigarette smokers will typically smoke over 15 cigarettes per day. So the overall smoke exposure is typically much greater with tobacco than with cannabis and this is a likely reason for the greater occurrence of tobacco-caused illness.

Chronic cannabis use is associated with the following health effects:
Increased risk of developing a psychotic illness
Respiratory diseases (e.g. bronchitis) and impaired lung function
Dependence (and an associated withdrawal syndrome)
Subtle disturbances of memory and attention
Cannabis use may also be associated with other health problems (e.g. lung cancer, and birth defects in children whose mother smoked cannabis during pregnancy) but the evidence is less clear for these problems.

Tobacco smoking, on the other hand, has been proven to cause a long list of diseases, including the three main causes of premature death: lung cancer, COPD and cardiovascular diseases. The status of tobacco as a legal form of drug use, its less marked psychological effects (e.g. not impairing judgment and driving ability), and the relatively short half-life of the active ingredient (nicotine half-life= 2 hours, versus days for THC) all lead to the tendency for users to take it very frequently (e.g. 15-20 cigarettes per day) and for a very long time (typically starting in teenage years and continuing daily into old age). Cannabis, on the other hand, is more commonly used either less than daily or once or twice per day, and users typically cease use prior to middle age.

So if one is to compare the health effects under typical use conditions, tobacco smoking is much more harmful to health. However, if one were to compare the effects on a “per smoke” basis then the two are likely of similar harmfulness, with cannabis having greater adverse psychological effects.

The human body was not built to inhale smoke of any kind, and whether it’s the result of burning tobacco, cannabis or lettuce, inhalation will cause damage in proportion to the quantity inhaled.
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About the Author


MA, MAppSci, PhD

Dr. Jonathan Foulds is an expert in the field of tobacco addiction.

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