The risk of lung cancer from cannabis use was restricted to the
upper tertile of joint-yrs of use, with a 5.7-fold greater risk in
those with .10.5 joint-yrs of cannabis use. However, it is
unlikely that this represents a threshold effect, as a linear
relationship has been clearly demonstrated between tobacco
cigarette consumption and risk of lung cancer [35]. The lack of
an association in the lower tertiles may be due to the relatively
small number of cannabis users in the study and the young age
of subjects reducing the time available for high numbers of
joint-yrs to accumulate, resulting in low levels of exposure (up
to 1.39 joint-yrs for the lower tertile).