Co-use of cannabis and tobacco in the same occasion: Acute effects. A systematic review.

Xu J.; Nette A.; Zakala C.; Zhao S.; Matheson J.; Wickens C.; Bonato S.; Di Ciano P. · Psychopharmacology · 2026

**Background & Methods** This systematic review synthesized evidence on acute effects of same-occasion cannabis and tobacco co-use across multiple study designs (RCTs, laboratory studies, epidemiological, qualitative, case reports, and observational studies). A comprehensive search of five databases (Embase, Medline, CINAHL, PsycINFO, Web of Science) from inception through May 2025 identified 18 peer-reviewed papers, theses, and grey literature examining cognitive, subjective, and physiological outcomes of co-use. **Key Findings** - **Cognition**: Three of five studies examining cognitive effects found that cannabis and tobacco each attenuated the effects of the other, though findings were inconsistent across studies, suggesting potential antagonistic rather than additive effects on cognitive performance. - **Subjective Experience**: Eight of twelve studies found no significant differences between co-use effects and individual drug effects. However, two studies reported tobacco dulled cannabis effects while two found tobacco enhanced cannabis's stimulant properties, indicating highly variable subjective outcomes depending on individual factors and study conditions. - **Physiological Measures**: Seven studies evaluated physiological outcomes with inconclusive results, failing to establish consistent patterns of additive, synergistic, or antagonistic effects on heart rate, blood pressure, or other physiological markers. **Dosage & Administration** Not reported. **Safety & Adverse Effects** Not reported. **Evidence Quality** This systematic review is limited by heterogeneous study designs, small sample sizes across included studies, and inconsistent outcome reporting, preventing meta-analytic synthesis. Studies were evaluated using SIGN methodology, but only 18 studies met inclusion criteria, indicating sparse literature on this topic. The mixed and inconclusive findings reflect methodological variability in cannabis dosing, tobacco administration routes, measurement timing, and participant populations. The authors note that large-scale, well-controlled studies investigating the full range of effects are needed. The evidence base does not support definitive conclusions about additive versus antagonistic effects, limiting clinical applicability and harm reduction guidance for co-users.

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