Pot Makes Kids Stupid: An extensive and broad study out of New Zealand finds that frequent marijuana use in people under 18 results in a measurable loss of IQ, the BBC reports.
Researchers followed 1,000 people from childhood to 38, so they were able to track changes in them before they started using cannabis, if they did.
The study took into account other factors such as education and drug and alcohol use, and found that those who smoked pot at least four times a week before the age of 18 suffered an average 8-point IQ loss. The IQ points did not fully return if the subjects stopped or reduced smoking.
The conclusion? Experts feel that marijuana smoking is relatively safe for adult brains, but it's dangerous for brains that are still developing.