Kanna (Sceletium tortuosum) is a South African medicinal plant sold, often as the standardized extract Zembrin, for stress and mood. Evidence in people is very small: a 3-month safety trial in 37 adults and one 20-person lab stress study.
Also known as: Sceletium tortuosum, Zembrin.
The safety trial used 8 mg or 25 mg of Zembrin once a day for 3 months (Nell 2013); the anxiety study used a single 25 mg dose (Reay 2020). These are study protocols, not a recommendation.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling.
What studies show: in a 3-month placebo-controlled trial in 37 healthy adults, 8 mg and 25 mg of Zembrin a day were well tolerated, with no changes in vital signs, heart tracings (ECG) or lab tests; the trial did not measure effects on mood or stress (Nell 2013). In two small experiments in 20 young healthy volunteers, a single 25 mg dose had no effect in the first, while in the second people reported less anxiety before a simulated public-speaking task; the authors call this the first tentative evidence (Reay 2020).
Safety: in the 3-month trial, the most common side effects (headache, abdominal pain and colds) were more frequent on placebo than on Zembrin (Nell 2013). The sources here do not describe drug interactions.
We could not find a single published half-life or time to peak for kanna that applies to a supplement dose, so we do not list one. Plant extracts are mixtures of many compounds, so no single figure would describe them.
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