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Study: Pot use after age 18 has less effect on IQ

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RICHMOND, Va. (WTVR)—New research suggests that smoking marijuana after age 18 will have less effects on mental functions.

While studies have previously questioned marijuana’s impact on intelligence, a new study indicates that the age a person first uses marijuana is a huge factor on later intelligence and mental function.  

The new study, by Duke University, was a decades-long study with over 1,000 New Zealand participants.

Researchers tested the IQs of 13-year-olds before marijuana use. They again tested their IQs at 38-years-old, after years of pot smoking.

The outcome of the study linked marijuana use at a young age to a decline in intelligence in adulthood, an irreversible decline. They found an average of an eight-point decline in intelligence levels. Researchers said this is not a huge, or negligible drop, reports CNN.

The simple synopsis by the lead scientist, Madeline Meier was that smoking marijuana as a teenager can literally make your intelligence drop.

“The effect of persistent cannabis use on intellectual functioning is really confined to adolescents, (which) suggests that adolescents, in particular, are vulnerable to the effect of cannabis,” said Meier.

The study also found people who started smoking pot as adults did not suffer any decline in intelligence. Co-author in the study, Richie Poulton said that the message is avoid marijuana use until adulthood, if possible.

In June, the Centers for Disease Control and Prevention reported that 23% of high school teenagers said they had recently smoked marijuana. The study also showed that for the first time, marijuana use had eclipsed cigarette smoking among teens.

Researchers think they know why prolonged pot smoking impacts the brains of teens and not adults.

Teenager’s brains are not fully developed and are more susceptible to the adverse impacts of marijuana. Marijuana could influence neural development, as synapses and neurons are still forming.

The new study was published Monday in the Proceedings of the National Academy of Sciences.

The bottom line is that the study makes ones of the strongest cases to date of a cause and effect relationship on marijuana use and mental ability.