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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?

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).

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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 low-level marijuana exposure.