A new study by the University of California San Diego (UC San Diego), the largest long-term study in the US on cannabis use, has found that the drug is negatively affecting teenage brains, particularly in younger users. The study, which tracked over 11,000 children from age 9 to 17, found that while some believe the substance can improve mood and energy, there are also negative effects on cognitive skills. The researchers found that those exposed to THC had worsened memory over time, while CBD did not. However, these findings do not necessarily prove a direct correlation between weed and cognitive impairment, as other factors such as environment or personality may play a role. The findings come as marijuana poisoning cases have increased 56% among New Yorkers under 19.