Colin Blakemore, PhD, ScD, Chair of the Department of Physiology at the University of Oxford, and Leslie Iversen, PhD, Professor of Pharmacology at the University of Oxford, wrote in their Aug. 6, 2001 op-ed in The Times (United Kingdom):

“It is claimed that cannabis smoke is more harmful to the lungs than tobacco smoke because it contains much the same mixture of noxious substances, and because cannabis users inhale more deeply and deposit more tar in their lungs. On the other hand, cannabis users do not smoke 20 to 40 times a day, as many cigarette smokers do. There may be a health risk, and it is compounded by the combination of cannabis with tobacco, but there is currently no indisputable evidence for a link with cancer.

The reports of cancers of the throat, mouth and larynx in cannabis users were based on small numbers and did not rule out effects of the concomitant use of tobacco. A much larger study in the United States monitored the health of a group of 65,000 men and women over a ten-year period. The 27,000 who admitted to having used cannabis showed no association between cannabis use and cancers, nor were there any other serious adverse effects on health.”

Aug. 6, 2001