A psychedelic formulation combining DMT and harmine, but not harmine alone, impaired convergent thinking—the ability to find a single correct solution—in 30 healthy men, especially those with higher baseline reasoning. Divergent thinking, the generation of many ideas, showed no overall effect but trended toward reduced fluency and elaboration. In a real-world painting task, both DMT/HAR and harmine reduced transitions associated with incubation, and DMT/HAR uniquely decreased the shift from incubation to illumination, indicating altered pathways to insight. Subjective experiences like altered meaning and insightfulness predicted divergent but not convergent thinking. The effects of DMT/HAR on creativity are not uniform, affecting both cognitive performance and the dynamic creative process.
A psychedelic formulation combining DMT and harmine impaired convergent thinking, especially in people with higher baseline reasoning, while harmine alone had no such effect. Divergent thinking showed no overall change, though there were trend-level reductions in fluency and elaboration under the combined formulation. In a real-world painting task, both the combined formulation and harmine alone reduced incubation-related transitions, and the combined formulation uniquely decreased transitions from incubation to illumination, suggesting altered pathways to insight. Subjective experiences like altered meaning perception and increased insightfulness predicted divergent, but not convergent, thinking outcomes. The effects of psychedelics on creativity are not uniform and depend on the cognitive stage and individual differences.