Harmful Cannabis Trumps Tobacco

Here's another hit to the proverbial groin of cannabis advocates. A recent advanced copy of scientific journal Thorax published a study claiming cannabis was 2.5-5 times worse than cigarettes.  I downloaded a copy of the paper, and have summarized its findings below.

Inclusion Criteria
339 people were recruited into four study groups

• Non Smokers (life time exposure of one pack per year of tobacco, 20 joints of cannabis)
• Cannabis Smokers (life time exposure of 5-joint years, with one joint per day)
• Smokers (one pack of cigarettes per day, for at least one year)
• Tobacco and Cannabis users (see above)

The researchers were careful to exclude non-users who yielded positive urine tests for either substance, as well as users of other drugs.  The study used a sample of opportunity (i.e. ads in newspapers, flyers), because of the 3500 random individuals they mailed questionnaires to, only 19 were suitable "cannabis only" users.

Although this will undoubtedly provide some bias in their data (towards those with a concern for their health), the authors argue, "This meant that many potential participants were ineligible, particularly the heaviest cannabis users who were more likely to have used other drugs. As a result, these criteria preferentially excluded such heavy users, suggesting that the effects observed may represent a conservative estimate."

Tests Performed
The following three categories of testing occurred on all subjects.

• Lung Function Tests (a barrage of physiological testing to determine how well the lungs are working)
• CT Scanning (to search for emphysema)
• Blood/Urine Tests (to measure metabolites of THC and nicotine)
• Questionnaires ( smoking history, passive smoking exposure, respiratory symptoms, family history, occupation and known respiratory illnesses, as well as their life time history of cannabis use and preferred method of use)

Study Results
Indeed, joint use was 2.5-5 times worse than tobacco cigarettes.  However, emphysema was not associated with cannabis users as was in tobacco smokers.

According to the authors, "In conclusion, these findings suggest that the predominant effects of cannabis on pulmonary structure, function and symptoms are in causing the symptoms of wheezing, cough, chest tightness and sputum production, large airways obstruction and hyperinflation, but not emphysema."

Interestingly, when subjects were asked to estimate the number of joints they had smoked over the life time (according to a reference in the present study, marijuana users are more accurate in remembering previous use then other drug users), there was a dose dependent response- the more you smoke, the worse the aforementioned symptoms are.

As an interesting side note about the habits of cannabis and tobacco users, the study also demonstrated that, "Cannabis smokers used similar amounts of cannabis whether or not they were also tobacco smokers. However, tobacco smokers who smoked cannabis smoked less tobacco than those who smoked tobacco alone, with a difference of 7.4 pack-years."

Study Implications
So why might cannabis be worse?  Well, from personal experience cannabis smokers a) don't filter the smoke they inhale as tobacco users do; b) inhale and keep the smoke in their lungs much longer than tobacco users.  Although, it is interesting to note that the smoker-group smoked 20 'coffin nails' a day compared to one joint.  That is plenty!

As for public health, the authors only had this to say, "The dose equivalence of 1:2.5–5 between cannabis joints and tobacco cigarettes in causing airflow obstruction is of major public health significance."

If marijuana joints are indeed worse than 'lung darts', might we expect to see more and more pot users sufferring from these afflictions?  

I'm not so sure.  As the authors' put,  "The requirement for cannabis smokers to have a history of at least 5 joint-years was based on the data that one cannabis joint results in three to five times higher levels of carbon monoxide and tar deposition, respectively, thereby achieving an a priori equivalence between the lower limit of cannabis and tobacco smoking levels."

That said, it seems for every year of pack-a-day smoking is near equivalent to 5 years of cannabis use.  However, if cannabis is 5 times worse per joint, as the study's upper limit suggest, then the two are on par (as long as both are being used according to the study's requirements)

What do NowPublic readers think?