4 Minutes
A small new brain-imaging study suggests people who use tobacco alongside cannabis show distinct changes in brain chemistry compared with those who use cannabis alone. The early results point to a molecular pathway that could help explain why co-use is often tied to worse addiction and mental health outcomes.
What the study measured and why it matters
Researchers compared brain scans from two groups: eight people who used only cannabis and five who reported using both tobacco and cannabis. Across several brain regions, the co‑use group showed significantly higher levels of a key enzyme called fatty acid amide hydrolase (FAAH). FAAH regulates the endocannabinoid system by breaking down anandamide, a neurotransmitter often associated with mood, reward and a sense of well‑being.
FAAH, anandamide and the endocannabinoid system — a quick primer
The endocannabinoid system is a neurochemical network that helps control mood, appetite, pain and reward. Anandamide is one of its primary signaling molecules; FAAH is the enzyme that degrades it. Higher FAAH activity generally means lower anandamide signaling. Animal work has suggested FAAH may also interact with nicotine reward pathways, but human evidence has been limited.
Key findings and expert reactions
The striking result was not just that FAAH levels differed, but how consistent that difference was across the small sample. "This is the first evidence in humans of a molecular mechanism that may underlie why people who use both cannabis and tobacco experience worse outcomes," said lead author Rachel Rabin from McGill University. Co‑author Romina Mizrahi, a psychiatrist at McGill, added that the researchers were surprised by how strong and distinct the effect appeared in co‑users compared with cannabis‑only users.
Why this could matter for addiction and mental health
Variants in the FAAH gene have been linked to higher risk of substance use disorders and anxiety in prior studies. If co‑use reliably raises FAAH or shifts endocannabinoid signaling, that might make people more vulnerable to nicotine and cannabis dependence or to anxiety and mood problems. Epidemiological research already shows that many young people who use both substances report more mental health symptoms than those who use only one.
Limitations: small numbers and unanswered questions
The new work is preliminary and observational. It did not include a tobacco‑only control group, so the change could result from tobacco alone, from an interaction with cannabis, or from other behavioral or genetic differences among participants. The study also lacked detailed measures of dose, frequency, vaping versus smoking, and the time since last use — all factors that could influence brain chemistry.
Where researchers go next
Authors emphasize the need for larger, controlled studies that separate tobacco‑only, cannabis‑only and co‑use groups, and that track changes over time. Future trials should include more diverse participants, account for vaping and cigarette use, and test whether FAAH or related pathways could be targeted to help treat co‑occurring cannabis and tobacco dependence.
Implications for users and clinicians
For now, the takeaway is cautionary rather than conclusive: tobacco and cannabis together may produce neurochemical changes that differ from cannabis alone, and these changes could help explain poorer outcomes in co‑users. Identifying a molecular link like FAAH opens a possible route for developing targeted treatments for people struggling with both substances, but it will take larger, rigorous studies to move from association to action.
Source: sciencealert
Leave a Comment