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Journal Club

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. JAMA. 2012;307(2):173–181. Study Objective.

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Journal Club

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  1. Journal Club Alcohol, Other Drugs, and Health: Current Evidence January–February 2012

  2. Featured Article Association between Marijuana Exposure and Pulmonary Function Over 20 Years Pletcher MJ, et al. JAMA. 2012;307(2):173–181.

  3. Study Objective • To analyze the association between current and lifetime marijuana use and pulmonary function.

  4. 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.

  5. Assessing Validity of an Article About Harm • Are the results valid? • What are the results? • How can I apply the results to patient care?

  6. 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?

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. What are the Results? • How strong is the association between exposure and outcomes? • How precise is the estimate of the risk?

  12. 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).

  13. 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?

  14. 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.

  15. Was the duration of follow-up adequate? • The follow-up period was 20 years.

  16. 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.

  17. Should I attempt to stop the exposure? • From a pulmonary standpoint, there appears to be no adverse impact from low-level marijuana exposure.

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