Adolescent THC exposure in mice caused persistent dysfunction in brain immune cells (microglia) that lasted into young adulthood but resolved with further aging.
Neuroscience researchers, parents, anyone interested in adolescent cannabis risk
Effects lasted to young adulthood but resolved by later adulthood
What the researchers found
Daily THC from postnatal day 30 to 44 produced microglia dysfunction in both male and female mice that persisted to young adulthood (PND70) but receded by PND120. The effects were prevented by a CB1 receptor antagonist and were not replicated when THC was given to adult mice.
Why it matters
Microglia play critical roles in brain development during adolescence. If THC disrupts their function during this window, it could impair the brain's ability to respond to infections and stress during a vulnerable developmental period.
The numbers in context
THC dose: 5 mg/kg daily for 14 days; dysfunction persisted to PND70 (young adulthood); resolved by PND120; effects blocked by CB1 antagonist
How the study worked
Mice received daily THC (5 mg/kg) during adolescence (PND30-44). Researchers examined microglia transcriptomes at PND70 and PND120, tested responses to immune challenge (LPS) and social stress (repeated social defeat), and used mass cytometry to map brain immune populations.
What this study cannot tell us
Animal study using injected THC at a single dose, which does not replicate human cannabis use patterns. Translating mouse developmental timelines to human adolescence is imprecise.
How to read the evidence
Well-designed animal study with multiple verification methods and controls, but findings need human confirmation.
When this study was published
Published in 2022
The bigger picture
This study provides a biological mechanism for why adolescent cannabis use may carry different risks than adult use. The finding that effects were adolescent-specific and reversible with aging adds nuance to the debate.
Questions still open
- Do lower THC doses or less frequent exposure produce similar microglial effects? Does this dysfunction contribute to the increased psychiatric risk observed in adolescent cannabis users?
Common questions
What are microglia and why do they matter?
Was the THC effect permanent?
Read the original research
Frequent Low-Dose Δ9-Tetrahydrocannabinol in Adolescence Disrupts Microglia Homeostasis and Disables Responses to Microbial Infection and Social Stress in Young Adulthood.
Biological psychiatry, 92(11), 845-860
Citation
Lee, Hye-Lim; Jung, Kwang-Mook; Fotio, Yannick; Squire, Erica; Palese, Francesca; Lin, Lin; Torrens, Alexa; Ahmed, Faizy; Mabou Tagne, Alex; Ramirez, Jade; Su, Shiqi; Wong, Christina Renee; Jung, Daniel Hojin; Scarfone, Vanessa M; Nguyen, Pauline U; Wood, Marcelo; Green, Kim; Piomelli, Daniele. (2022). Frequent Low-Dose Δ9-Tetrahydrocannabinol in Adolescence Disrupts Microglia Homeostasis and Disables Responses to Microbial Infection and Social Stress in Young Adulthood.. Biological psychiatry, 92(11), 845-860. https://doi.org/10.1016/j.biopsych.2022.04.017
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