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The study in “Marijuana may boost heart attack risk” appears to be more about the effects of smoking and deep inhalation than a useful examination of the effects of tetrahydrocannabinol, which is what marijuana smokers seek. The report makes it sound as though this active ingredient is the cause of the marginal increase in heart attacks, whereas it is probably due to smoking–whether that be of marijuana, tobacco, or oak leaves. Marijuana smokers inhale unfiltered smoke and hold it in their lungs for a prolonged period. A major component of this smoke (as well as that of cigarettes) is carbon monoxide. This will cause, of course, a sudden reduction in blood-oxygen partial pressure and affect a heart already partially oxygen-compromised by coronary artery disease. Peter Nelson
Nevada City, Calif.