AAP - published in the Australian January 12, 2012
PEOPLE who occasionally smoke marijuana do not suffer long-term lung damage the way cigarette smokers do and may actually experience a slight improvement, a new study says.
Since the research included more than 5000 people older than 20, the authors said it should help clear up some of the confusion about the risks of marijuana smoking.
However, they warned that the danger of heavy marijuana use was difficult to assess and cautioned against regular or frequent smoking.
"Marijuana is still an illegal drug and it has many complicated effects on the human body and its function," said Stefan Kertesz, senior author of the research published yesterday in the Journal of the American Medical Association.
"In our findings we see hints of harm in pulmonary function with heavy use and other studies have shown that marijuana use increases a user's likelihood of a heart attack . . . and impairs the immune system's ability to fight disease."
Researchers recruited subjects between the ages of 18-30 in four US cities and followed them from 1985 to 2006. They measured "joint-years" in which one joint-year of exposure would be the equivalent of smoking 365 joints or pipe bowls.
For those who reported smoking an average of one joint a day for seven years, or one joint a week for 49 years, the study found no harmful lung effects resulted.
Researchers at the University of Alabama division of preventive medicine and at the Veterans Affairs Medical Centre in Birmingham, measured lung function by assessing the force and volume of each person's exhale.
Those who smoked cigarettes tended to have much higher lifetime exposure to smoking than marijuana users, but when researchers adjusted the data for current and lifetime exposure, they found smokers' lung function got worse over time while pot smokers' lung function actually improved slightly.
"However, the gains . . . were so small that most people would likely not notice at all," he said.