A large study found that moderate cannabis use in adults over 40 was linked to larger brain volumes and better cognitive function, though experts caution more research is needed before drawing conclusions. A landmark longitudinal study published in JAMA Health Forum followed 463,396 adolescents ages 13-17 through age 26. Past-year cannabis use during adolescence was associated with a doubled risk of developing psychotic and bipolar disorders, plus elevated risks for depression and anxiety.