According to the 12 June 2001 issue of Circulation, middle-aged marijuana smokers are at significantly increased risk of myocardial infarction (MI), especially during the hour immediately following smoking.

Dr. Murray A. Mittleman, of Beth Israel-Deaconess Hospital, in Boston, and colleagues collected data from 2624 men and 1258 women who had been treated for first MI at 62 participating medical centers. The subjects were interviewed an average of 4 days after infarction onset.

Of the study participants, 124 reported smoking marijuana at some point within the year prior to the myocardial infarction. Of these, 37 had smoked marijuana within 24 hours before MI, and 9 had smoked within an hour before symptom onset.

Three quarters of the MI survivors who were marijuana users were younger than 50 years of age, and the others were 50 to 69 years of age. In contrast, 30% of the nonusers were aged 70 years or older. The marijuana users were less likely than nonusers to be hypertensive, diabetic or have a history of angina. They were twice as likely to be tobacco smokers and much more likely to be obese.

During the first hour after smoking marijuana, there was a 4.8 fold increase in the relative risk of heart attack, the authors emphasize. However, the risk returned to baseline after an hour.

"Smoking marijuana is a rare trigger of acute myocardial infarction and may pose a health risk to patients with established coronary artery disease and perhaps to individuals with multiple coronary risk factors," the researchers conclude.