Kanna (Sceletium tortuosum) is a South African succulent traditionally used by indigenous peoples for its mood-enhancing properties. Recent scientific interest has focused on its effects on the serotonin system. Kanna contains alkaloids such as mesembrine, which are known to act as selective serotonin reuptake inhibitors (SSRIs) and phosphodiesterase-4 (PDE4) inhibitors. Several in vitro and animal studies have demonstrated that these alkaloids can inhibit the reuptake of serotonin, thereby increasing its availability in the synaptic cleft and potentially contributing to mood elevation or anxiolytic effects.

Human clinical evidence is limited but growing. A small number of double-blind, placebo-controlled studies have shown that standardized Kanna extracts can reduce anxiety and improve cognitive flexibility, likely via serotonergic pathways. However, these studies are few, often involve small sample sizes, and are sometimes funded by supplement manufacturers. Thus, while the mechanistic basis for Kanna’s serotonergic action is supported by preclinical research and there is some early clinical evidence, high-quality, large-scale trials are lacking.

In summary, Kanna's use for supporting the serotonin system is grounded in both traditional use and preliminary scientific validation, particularly due to its SSRI-like activity. However, the current level of clinical evidence is moderate and further research is needed for definitive conclusions.