CANNABIS CLAIMS GO UP IN SMOKE

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