One of key arguments opponents of legal marijuana is underage age use going up and it is bad for kids. Everyone is in agreement, but the same can be said of nicotine and alcohol, thus age limits. While increased underage going up argument has been disproven, there still are concerns about the effects of still developing brain. No one in industry is advocating for a 10 year old to vape, just as no one is serving a 10 year old a whiskey sour. But is someone who starts using at 24 years affected, well a study weighs in on cannabis and IQ.
A large study in New Zealand found that persistent marijuana use disorder with frequent use starting in adolescence was associated with a loss of an average of 6 or up to 8 IQ points measured in mid-adulthood.43 Those who used marijuana heavily as teenagers and quit using as adults did not recover the lost IQ points. People who only began using marijuana heavily in adulthood did not lose IQ points.
An earlier study conducted in 2001 and published in the journal Archives of General Psychiatry revealed that “the former marihuana smokers did not show any cognitive impairments,” the same as a study published four years later in the journal Neurotoxicology and Teratology.
A study conducted in 2001 and published in the journal Archives of General Psychiatry revealed that “the former marihuana smokers did not show any cognitive impairments,” the same as a study published four years later in the journal Neurotoxicology and Teratology.
On the other end of the spectrum are studies suggesting the opposite. As a rule, those kinds of studies mainly focus on the long-term outcomes of those who started using marijuana earlier in life, comparing statistically significant changes in cognitive functioning among those who use cannabis and those who don’t.
The New Zealand study followed 1,037 New Zealanders from age 3 to age 45 to determine the effect marijuana has on brain function. Published in The American Journal of Psychiatry, the study found that those who have been using cannabis early and long-term and on a regular basis showed cognitive impairment after all.
Besides a 5.5 points decline in users’ IQs from childhood to midlife, the results confirmed some deficits in learning and processing speed compared to those who are not marijuana users.
One key note is, as with alcohol, long-term cannabis users also developed memory and attention problems, the study found. And like alcohol and nicotine, early age use of marijuana can have long term negative effects. More research needs to be done regarding adult use.