Several studies have previously argued that cannabis lowers IQ levels. For instance, a large New Zealand study of 1,000 individuals measured the IQs of participants at the age of 13, and again at 38, while assessing pot smoking habits in the interim period. The study found that individuals who had reached the age of 18 and had become addicted to cannabis experienced a drop in their IQ scores when measured again at the age of 38. According to this study, it does appear that cannabis lowers IQ.
Although this study has been criticized as it did not control for other life choices during the two IQ testing periods, it has corroborated previous studies find also speculated that cannabis lowers IQ. A new Canadian study also examined whether cannabis lower IQ. The eight year study followed 70 teenagers, who had their IQ tested at the age of 12 and again between the ages of 17 and 20. The study found that teenagers who smoked more than five joints per week experienced an average IQ drop of 4 points. Although this may not sound like a big drop, it’s important to be reminded that 50% of the population have IQs of less than 100. So losing four points will not provide do anyone any favors.