Children's Health

Study: Early Marijuana Use May Increase Brain Damage

Marijuana is shown for sale at the San Francisco Medical Cannabis Clinic in San Francisco, Friday, Oct. 15, 2010. Attorney General Eric Holder says the federal government will enforce its marijuana laws in California even if voters next month make the state the first in the nation to legalize the drug. (AP Photo/Eric Risberg)

Marijuana is shown for sale at the San Francisco Medical Cannabis Clinic in San Francisco, Friday, Oct. 15, 2010. Attorney General Eric Holder says the federal government will enforce its marijuana laws in California even if voters next month make the state the first in the nation to legalize the drug. (AP Photo/Eric Risberg)  (AP)

Smoking marijuana at a young age causes more brain impairment than those who use the drug later in life or not at all, according to a study from McLean Hospital of the Harvard School of Medicine.

The small study shows that smoking marijuana before the age of 16 leaves individuals with weakened executive function, such as planning, flexibility and abstract thinking.

One of the tests conducted as part of the study included subjects being asked to sort a deck of cards following one set of rules, and then quickly switching to another set of rules without warning. The individuals who started smoking at an early age performed significantly worse than non-users and those who started using marijuana later in life.

In other tests, early marijuana users continued to make the same errors repeatedly.

The study included 33 young marijuana users and 26 non-users.

Previous studies by neuroscientists had shown that those who smoke large amounts of marijuana on a regular basis do not do well on tests of memory and other mental abilities.

Click here to read more on the study from McLean Hospital.