Both Tobacco and Cannabis Smoking Activated the Same Inflammatory Immune Pathway in Young Adults

In a cohort of 62 primarily African American young adults, researchers measured a specific immune marker: GPR15 expression on helper T cells. Both tobacco and cannabis smoking were strongly associated with increased GPR15 expression (p < 0.001), and that increase was in turn strongly associated with a shift toward pro-inflammatory cytokine ratios.

The key finding was the mediation analysis: increased GPR15 expression accounted for roughly half of the relationship between smoking (either substance) and pro-inflammatory immune markers. In other words, GPR15 appeared to be a major pathway through which both tobacco and cannabis drive systemic inflammation.

This was notable because cannabis and tobacco smoke have different active compounds (THC/cannabinoids vs nicotine) but share the combustion products — tar, carbon monoxide, particulate matter. The shared GPR15 pathway suggests it's the smoke itself, not the specific drug, driving much of the inflammatory response.

This study bridged cannabis and tobacco research by showing they share an inflammatory mechanism. The implication is direct: if you smoke cannabis, your immune system responds to the combustion much like it responds to tobacco smoke. The active ingredient may be different, but the inflammatory damage from inhaling burned plant matter is similar.

This matters for the "cannabis is safer than tobacco" narrative. For the specific dimension of systemic inflammation via inhaled smoke, they appear to be comparably harmful. Vaporizing or edibles would avoid this pathway entirely.