Benefits
Calm and anxiety response during stressful tasks
In a brain-imaging study in 16 healthy adults, a single 25 mg dose of the standardized extract lowered the amygdala's reaction to fearful faces and its coupling to the hypothalamus. In a laboratory stress study, a single 25 mg dose went with lower reported anxiety before a public-speaking task, though a separate multitasking task showed no change. All of this used the branded extract.
Executive function and mental flexibility under cognitive load
In a 3-week crossover study in 21 healthy adults, 25 mg a day of the standardized extract improved cognitive set-flexibility and executive-function scores compared with placebo, measured on a computer test battery. Mood and sleep ratings also shifted positively. The study was small and used the branded extract.
Reaction and visual tracking under a cognitive load
In 60 recreationally trained adults aged 20 to 35, 8 days of 25 mg a day of the standardized extract improved performance on a complex reaction task that added a cognitive load, compared with placebo. Simple reaction tasks and self-rated alertness did not change. This was a short study of the branded extract in young, active people.
Mood and sense of well-being
Kanna was traditionally used as a mood enhancer. In the cognition study, mood ratings shifted positively alongside the thinking results, and a 3-month safety study logged unsolicited diary notes of better coping with stress. A controlled trial that measured overall mood in young adults found no change, so the human evidence for mood is thin.
Calm without daytime drowsiness
Kanna is traditionally described as calming but not heavily sedating. In a 3-month safety study of 8 mg and 25 mg a day in healthy adults, the extract was well tolerated, with no sedation signal and with headache reported less often than on placebo. This reflects tolerability and traditional use, not a proven effect on anxiety.
Mechanism of action
Serotonin reuptake blocking in the lab
In test-tube assays a standardized Sceletium tortuosum extract was a potent blocker of the serotonin transporter, with mesembrine the most active single alkaloid. Blocking reuptake leaves more serotonin in the synapse. This is laboratory pharmacology and is not a claim that kanna acts as a medicine.
PDE4 inhibition and cAMP signaling in the lab
The same laboratory work found the extract strongly inhibited the enzyme PDE4, which breaks down the cell messenger cAMP; mesembrenone was active here. Higher cAMP is one proposed reason for possible effects on mood and thinking, but this comes from cell and enzyme studies, not from people.
Lower threat reactivity in the brain
In a human brain-imaging study, a single 25 mg dose of the standardized extract reduced how strongly the amygdala responded to fearful faces and weakened its link to the hypothalamus. The authors read this as a possible biological basis for a calming effect, shown in a single small study.
Clinical trials
Double-blind, placebo-controlled crossover pharmaco-fMRI study of a single 25 mg dose of the standardized Sceletium tortuosum extract Zembrin. (Terburg et al. 2013, Neuropsychopharmacology)
16 healthy adults scanned during perceptual-load and emotion-matching tasks.
A single 25 mg dose lowered amygdala reactivity to fearful faces under low perceptual load and reduced amygdala-to-hypothalamus coupling versus placebo. This is a brain-activity marker in a very small group, not a measure of day-to-day anxiety symptoms.
Randomized, double-blind, placebo-controlled crossover proof-of-concept study of 25 mg a day of Zembrin for 3 weeks, with an author employed by the extract maker. (Chiu et al. 2014, Evid Based Complement Alternat Med)
21 cognitively healthy adults, mean age about 55 years.
Zembrin significantly improved cognitive set-flexibility (P < 0.032) and executive function (P < 0.022) versus placebo on a computer test battery, with positive changes in mood and sleep. The trial was small, short and maker-linked.
Two placebo-controlled, double-blind, between-subject studies of a single 25 mg dose of Zembrin against laboratory stress tasks. (Reay et al. 2020, Hum Psychopharmacol)
20 young healthy volunteers across a multitasking study and a public-speaking study.
Results were mixed: the multitasking study showed no treatment effect, while the public-speaking study found lower subjective anxiety in the Zembrin group before the task and a treatment-by-time effect on heart rate. The authors called it first tentative evidence.
Randomized, placebo-controlled study of 25 mg a day of a Sceletium tortuosum extract for 8 days, testing reaction, visual tracking and mood. (Hoffman et al. 2020, J Strength Cond Res)
60 recreationally trained adults aged 20 to 35 (48 men, 12 women).
The extract improved performance on a complex reaction task with a cognitive load versus placebo, but there was no change in simple reaction, self-rated alertness or total mood score. A short study in young, active people.
Randomized, double-blind, parallel-group, placebo-controlled safety study of 8 mg and 25 mg a day of Zembrin for 3 months; no efficacy outcomes were measured. (Nell et al. 2013, J Altern Complement Med)
37 healthy adults (12 on 8 mg, 12 on 25 mg, 13 on placebo).
Both doses were well tolerated over 3 months, with no concerning changes in vital signs, ECG or blood tests and headache reported less often than on placebo. The study set out to test safety, not benefits; any positive comments were unsolicited diary notes.