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

The takeaway

A 30-day cannabis smoke study found opposite effects by age: smoke increased hippocampal inflammation in young mice but decreased it in aged mice — suggesting cannabis's brain effects fundamentally depend on age.

Older adults considering cannabis, neuroscientists, aging researchers, and anyone interested in why cannabis effects vary by age.

What the researchers found

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.

Why it matters

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.

The numbers in context

Young mice: 4 months. Aged mice: 22 months. 30 days daily smoke exposure. Cannabis: 5.5-6.2% THC. Hippocampus: age-dependent cannabis effects on multiple cytokines. PFC and serum: minimal cannabis effects. IL-13 and Dkk1: age-related increases attenuated by cannabis in aged mice.

How the study worked

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.

What this study cannot tell us

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 Preprint (not yet peer-reviewed).

How to read the evidence

Novel preclinical finding with consistent age-dependent pattern, but preprint status and mouse model limit conclusions.

When this study was published

Published as 2026 preprint, first study systematically comparing cannabis smoke effects on brain inflammation across young and aged subjects.

The bigger picture

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.

Questions still open

Would pure THC or CBD show the same age-dependent effects? Is the hippocampal specificity related to memory effects of cannabis? Could anti-inflammatory cannabis treatments be developed specifically for older adults?

Common questions

Does cannabis affect young and old brains differently?

This mouse study found the effects are actually opposite: cannabis smoke increased brain inflammation in young mice but reduced it in aged mice, particularly in the hippocampus (the memory center). If confirmed in humans, this could explain very different cannabis outcomes by age.

Could cannabis reduce brain inflammation in older adults?

In aged mice, cannabis smoke did reduce several inflammatory markers in the hippocampus. However, this is early animal research — translation to human treatment requires much more study, especially regarding the best form and dose.

Read the original research

Effects of Chronic Cannabis Smoke Exposure on Inflammatory Markers in Periphery and Brain in Young and Aged Mice.

bioRxiv : the preprint server for biology

View on PubMed ↗Publisher’s paper ↗

Citation

Gazarov, Emely A; McCracken, Bailey; Krumm, Zachary A; Zequeira, Sabrina; Setlow, Barry; Bizon, Jennifer L. (2026). Effects of Chronic Cannabis Smoke Exposure on Inflammatory Markers in Periphery and Brain in Young and Aged Mice.. bioRxiv : the preprint server for biology. https://doi.org/10.64898/2026.02.06.703827