Pubdate: Thu, 14 Nov 2002
Source: Guardian, The (UK)
Copyright: 2002 Guardian Newspapers Limited
Author: Clive Bates


The claim that smoking three cannabis joints a day would damage the lungs 
as much as 20 cigarettes a day needs its own health warning (Report, 
November 11). The two 1987 studies on which this claim appears to be based 
examine a limited range of symptoms, and did not estimate the risks of lung 
cancer and chronic obstructive pulmonary disease (COPD, eg emphysema), 
which are the main fatal lung diseases caused by smoking tobacco. The 
report calls for more research "to establish what link (if any) there is 
between COPD and cannabis smoking". Given that the data don't cover the 
main risks, it is premature to draw precise risk comparisons between 
cannabis and tobacco.

This is not to argue that cannabis is safe. The most important factor will 
be lifetime exposure. Because tobacco is so addictive, it is not unusual 
for a smoker to consume 20 cigarettes a day for 40 years. But such heavy 
and sustained cannabis use is rare. Any comparison of risk needs to include 
the different ways the products are used over a lifetime; the neat 3:20 
formulation cannot do that.

Clive Bates,

Director, Ash
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