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Marijuana Linked to Respiratory Complications


NEW HAVEN, Conn. -- In the long run, smoking marijuana has many of the same effects as smoking cigarettes, such as coughing and wheezing, according to researchers here.

NEW HAVEN, Conn., Feb. 14 -- In the long run, smoking marijuana has many of the same effects as smoking cigarettes, such as coughing and wheezing, according to researchers here.

So found a Yale-led team on the basis of a systematic review of 34 studies that evaluated the effect of marijuana smoking on pulmonary function and respiratory complications and bronchodilation, reported Jeanette Tetrault, M.D., and colleagues, in the February issue of Archives of Internal Medicine.

"While there is convincing data on the effects of tobacco smoke on pulmonary clinical outcomes, the effect of marijuana smoke has been poorly understood," Dr. Tetrault said.

To attempt to fill the gap, she and colleagues divided eligible studies into three groups - challenge studies that experimentally examined airway response to marijuana smoke, studies that looked at changes in pulmonary function associated with long-term use, and studies that looked at respiratory complications associated with long-term use. Some studies fell into more than one category.

All of the 14 studies that looked at respiratory complications found an association with long-term marijuana use, Dr. Tetrault and colleagues found. For example, one large cross-sectional study showed that marijuana smoking, compared with controls, was associated with increased odds of:

  • Cough (with an odds ratio of 2.00 and a 95% confidence interval from 1.32 to 3.01).
  • Phlegm (with an odds ratio of 1.89 and a 95% confidence interval from 1.35 to 2.66).
  • Wheeze (with an odds ratio of 2.98 and a 95% confidence interval from 2.05 to 4.34).
  • All comparisons were significant at P<0.01.

The researchers found 12 studies that used a laboratory challenge design using various measures including specific airway conductance, forced expiratory volume in one second (FEV1) peak flow, airway resistance, and change in methacholine- or exercise-induced bronchospasm.

Most of the studies, regardless of the measure used, reported a bronchodilating effect soon after smoking marijuana, the researchers said.

For example, of the seven studies that measured specific airway conductance, six showed increases of between 8% and 48%. Similarly, of the five that measured FEV1, three showed increases of between 0.15 and 0.25 liters and one showed no effect.

On the other hand, one study measured the effect on specific airway conductance of marijuana use over 47 to 59 days and showed a significant (at P<0.001) decrease over baseline, as well as a decrease in FEV1.

Fourteen studies assessed the impact of long-term marijuana use on pulmonary function, Dr. Tetrault and colleagues said, and the results were mixed.

Overall, however, the studies failed to show a clear association between long-term use and changes in the ratio of FEV1 to forced vital capacity (FVC), in the diffusing capacity of the lung for carbon monoxide (DLCO), or in airway hyper-reactivity.

The researchers noted that the study quality varied greatly. Many, for example, failed to account for confounding factors such as tobacco or other inhaled drugs, there was no standard measure for drug exposure, and outcome measures were not standardized.

Nevertheless, they concluded, "this review should alert primary care physicians to the potential adverse health outcomes" associated with using marijuana.

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