Cannabis Smoke Reduced Brain Inflammation in Old Mice But Increased It in Young Mice

Aging caused significant increases in hippocampal cytokines. Cannabis smoke interacted with age in the hippocampus: exposure tended to increase cytokine levels in young mice but decrease them in aged mice, including attenuating age-related increases in IL-13 and Dkk1. Effects were largely restricted to the hippocampus, with minimal impact in prefrontal cortex or blood.

Young (4 months) and aged (22 months) C57Bl/6J mice exposed to cannabis (5.5-6.2% THC) or placebo smoke daily for 30 days. Blood, prefrontal cortex, and hippocampus analyzed for multiple inflammatory markers. Both individual cytokine comparisons and global profiles assessed.

This is one of the first studies to show cannabis smoke has fundamentally different effects on brain inflammation depending on age. If confirmed, it could explain why cannabis appears to help some older adults while potentially harming younger users — a critical distinction for clinical guidance.

This age-dependent flip in cannabis effects could be paradigm-shifting. The aging brain has chronic low-grade inflammation that cannabis may reduce, while the young brain's normal immune surveillance may be disrupted by cannabis. This aligns with clinical observations of different cannabis outcomes by age.

Mouse model — effects may not translate to humans. Cannabis smoke includes non-cannabinoid compounds. 30-day exposure only. Specific THC dose delivered via smoke is variable. C57BL/6 strain may not represent all genetic backgrounds. Preprint (not yet peer-reviewed).