B O S T O N, June 12, 2001 -- Thinking of chilling out in your middle age by kicking back and lighting up a joint?

Think again. A new study from Boston's Beth Israel Deaconess Medical Center and Harvard Medical School says marijuana increases the risk of having a heart attack within the first hour of smoking to five times that of non-smokers.

Within the second hour, the risk declines to 1.7 times normal; and returns to an average risk after 2 hours.

The study, lead by Beth Israel director of cardiovascular epidemiology Dr. Murray Mittleman, is reported in this week's issue of the American Heart Association journal Circulation.

Marijuana Like Sex Risk

Mittleman and colleagues interviewed more than 3,880 men and women aged 20 to 92 who had suffered heart attacks to determine what activities were most likely to happen just before a heart attack, during a time frame the doctors call the "hazard period."

One-hundred-and-twenty-four subjects said they had smoked marijuana within the year before their heart attack

The scientists say that this five-fold marijuana risk is a little higher than the risk for sexual intercourse, about the same as that for other types of strenuous exercise, and much less than the risk caused by cocaine, which increases one's chance of having a heart attack 25-fold.

These risks are compounded by other lifestyle conditions that affect heart function, such as such as smoking cigarettes, being overweight, and not participating in physical activity.

Risk Increases With Age

The study also points out marijuana risk could be even higher because the survey did not include people who had heart attacks after smoking who did not survive.

Moreover, Mittleman emphasizes that the five-fold marijuana risk statistic is an average, and that risk levels for young people are probably much less than five times and the risk levels for older people are probably much greater.

"As with any risk factor for heart attack, or for heart disease in general, the risks become more pertinent as we grow older. Marijuana use is no exception," Mittleman says. "As baby boomers enter the age at which coronary disease is the most important cause of death and the leading cause of morbidity [death], we may see an increase in marijuana-associated heart attacks."

What About Pot’s Calming Effect?

But isn't marijuana suppposed to be relaxing?

Well, yes and no. Marijuana seems to have a wide range of effects on people and can be quite different for each individual. Many regular smokers report feeling relaxed, high, happy, and peaceful, along with sleepiness and "the munchies' — extreme thirst and hunger.

But numerous other people, especially those who smoke only occasionally, report feeling depressed, anxious, and paranoid, along with a number of physical symptoms including tremors and breathing irregularities.

Scientists believe smoking marijuana puts a strain on your heart although are not sure whether it is the active ingredient tetrahydrocannabinol (THC) itself or other substances within the inhaled smoke, such as carbon monoxide and burnt plant particles, that have negative effects on the heart.

Previous studies have shown marijuana causes increased heart rate, fluctuations in blood pressure, and a decreased ability for the blood to carry oxygen. The heart is both working harder and getting less oxygen, a situation that increases heart attack risk.

Marijuana could also trigger a heart attack by disrupting the cholesterol plaques that line the blood vessels of people with artery disease. If pieces of plaque break off they can clog the vessels that carry oxygen to the heart and ultimately cause a heart attack.