Comparing cannabis with tobacco: Arithmetic does not add  up

doi:10.1136/bmj.327.7407.165

BMJ 2003;327:165 (19 July), doi:10.1136/bmj.327.7407.165

Letter

Comparing cannabis with tobacco

Arithmetic does not add up

The first 150 words of the full text of this article appear below.

EDITOR—The editorial by Henry et al comparing cannabis with tobacco implies that in the future as many as 30 000 deathsa year in Britain may be caused by smoking cannabis.¹ Butthis conclusion seems to have been based on a series of questionable assumptions.

To expose the lungs to the same amount of tar as an averagecigarette smoker (15-20 a day), cannabis users would have tosmoke four to five times a day, every day of the week. In fact,surveys show that a large majority in Britain are occasional"weekend" users, and few fall into the high use category offour to five times a day.

Another important factor is that unlike cigarette smokers mostcannabis smokers tend to stop when they reach their 30s. Longterm surveys of cigarette smokers showed that those who stopbefore the age of 35 had only a very . . . [Full text of this article]

Les Iversen, professor

Department of Pharmacology, University of Oxford, Oxford OX1 3QT les.iversen@pharm.ox.ac.uk