Transcript Journal Club Alcohol, Other Drugs, and Health: Current Evidence January–February 2012 Featured Article Association between Marijuana Exposure and Pulmonary Function Over 20 Years Pletcher MJ, et al.

Journal Club
Alcohol, Other Drugs, and Health: Current Evidence
January–February 2012
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Featured Article
Association between
Marijuana Exposure
and Pulmonary Function Over
20 Years
Pletcher MJ, et al. JAMA. 2012;307(2):173–181.
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Study Objective
• To analyze the association between current and
lifetime marijuana use and pulmonary function.
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Study Design
• Longitudinal study* that assessed pulmonary
function and smoking from 1985–2006 in a cohort
of 5115 men and women from 4 US cities.
• Participants underwent baseline examination and 6
follow-up examinations.
• Pulmonary function testing was performed at
baseline and years 2, 5, 10, and 20.
• Lifetime exposure to marijuana was expressed in
joint-years, with 1 joint-year of exposure equivalent
to smoking 365 joints or filled pipe bowls.
*Coronary Artery Risk Development in Young Adults (CARDIA) study.
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Assessing Validity of an
Article About Harm
• Are the results valid?
• What are the results?
• How can I apply the results to
patient care?
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Are the Results Valid?
• Did the investigators demonstrate similarity in all
known determinants of outcomes? Did they
adjust for differences in the analysis?
• Were exposed patients equally likely to be
identified in the two groups?
• Were the outcomes measured in the same way in
the groups being compared?
• Was follow-up sufficiently complete?
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Did the investigators demonstrate similarity in
all known determinants of outcomes? Did they
adjust for differences in the analysis?
• Mixed linear modeling was used to account for
individual age-based trajectories of pulmonary
function and other covariables*, including tobacco
use, which was analyzed in parallel as a positive
control.
• Approximately equal numbers of self-identified
“black, not Hispanic” and “white, not Hispanic” men
and women were recruited to ensure an adequate
sample of the largest minority group in the US at
baseline (1985).
*Race, sex, age, height, waist circumference, secondhand smoke exposure, exposure to
airborne particulates (using study-city yearly averages), education level, and asthma.
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Were exposed patients equally likely
to be identified in the groups?
 Yes.
− The sample included only participants (n=5016)
whose visits provided complete data on pulmonary
function, smoking behavior (tobacco and
marijuana), secondhand smoke exposure, height,
and waist circumference.
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Were the outcomes measured in the
same way in the groups being compared?
 Yes.
− Forced expiratory volume in the first second of
expiration (FEV1) and force vital capacity (FVC)
were measured in the same way for all
participants.
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Was follow-up sufficiently complete?
• Participants contributed an average of 3.9
pulmonary-function measurements per
person over the course of 20 years.
• Fifty-six percent of the sample (2807
participants) attended the year-20
examination.
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What are the Results?
• How strong is the association between
exposure and outcomes?
• How precise is the estimate of the risk?
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How strong is the association between
exposure and outcome?
How precise is the estimate of the risk?
• In adjusted models that considered 4-level
categorizations of current and lifetime exposure,
compared with zero exposure,
– FVC increased with greater lifetime exposure in joint-years (p=0.01), and
FEV1 increased with greater lifetime exposure of up to 10 joint-years and
then declined to 36 mL (95% CI, −6.5 to 79) greater than the zero
exposure level (p=0.049).
– FVC increased with smoking intensity up to 20 marijuana smoking
episodes in the past 30 days and then declined to 20 mL greater than the
zero exposure level (p=0.03).
How Can I Apply the Results to
Patient Care?
• Were the study patients similar to the patients
in my practice?
• Was the duration of follow-up adequate?
• What was the magnitude of the risk?
• Should I attempt to stop the exposure?
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Were the study patients similar to the
patients in my practice?
• The sample was comprised of black and white
women and men from 4 large US cities who
were aged 18–30 years and healthy at
enrollment in 1985.
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Was the duration of follow-up adequate?
• The follow-up period was 20 years.
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What was the magnitude of the risk?
• Low level marijuana exposure was not
associated with declines in pulmonary
function.
• The study was not able to confirm whether
heavy marijuana exposure was associated
with impairments in pulmonary function.
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Should I attempt to stop the exposure?
• From a pulmonary standpoint, there
appears to be no adverse impact from lowlevel marijuana exposure.
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