A new research has revealed that the use of marijuana at an early age lead to harmful effects on brain.

The study led by researcher Staci Ann Gruber, PhD, of Harvard Medical School and McLean Hospital, Boston suggests that young adults who start having marijuana before age 16 are more likely to get affected by cognitive impairment later in life. Also, those, who start smoking early, are three-times more likely to smoke more.

The assessment was made on 35 chronic marijuana smokers and the control group was taken as 29 healthy people. Out of the total participants, 20 began smoking marijuana before 16 years of age and 15 commenced the same after the age of 16.

Participants underwent a card-sorting task, so as to assess their cognitive flexibility. The cards were of distinct colors, shapes, numbers and forms. They had to sort the cards without telling them the way to do so. Then, the rule for sorting the cards was changed.

It was found that the tests were carried out well by healthy people in comparison to the marijuana smokers and the early-onset smokers. There was repetition of mistakes by the early-onset smokers, though they were made aware about the rules. They made 14.2 errors, as compared to 6.4 mistakes made by late-onset smokers.

"The early-onset smokers may have trouble with abstract thinking, for instance, or may say something socially inappropriate", said Gruber.