What the Research Says About Kanna, Stress and Focus
A brain scan, a mock public speech, reaction tasks and memory tests. Here is what each measured, what moved, what did not, and how much weight it can bear.
When people search for what the research says about kanna and stress, or kanna and focus, they are looking for a short list of lab studies that tend to get over-summarized. Here they are, one by one: the brain-scan study, the mock public speech, the reaction task and the cognitive battery. Each is a small experiment in healthy volunteers using one branded extract. None shows that kanna helps with stress, anxiety or attention in daily life.
Four small studies of the Zembrin kanna extract (mostly 25 mg) measured lab-stress and thinking outcomes in healthy adults. One reported lower amygdala activity to fearful faces, one reported lower anxiety ratings before a mock speech (while a second experiment found nothing), one found better cognitive flexibility, and one a better complex reaction task. Most other measures showed no difference.
What did the kanna amygdala study measure?
It measured brain activity on an fMRI scanner, not stress or feelings. In 2013, Terburg and colleagues scanned 16 healthy undergraduates aged 18 to 21 twice, 5 to 9 days apart, once after a single 25 mg dose of Zembrin and once after placebo, in a double-blind crossover [1].
In a task that varied how busy the viewer's attention was, amygdala activity to fearful versus neutral faces was lower after Zembrin when the task load was low. The effect was not significant when load was high. In a second task, connectivity between the amygdala and hypothalamus was lower. Task errors and reaction times did not differ, the authors saw no general effect on subjective mood, and one of the 16 participants was excluded for near-chance performance [1].
The amygdala is a brain region involved in responses to threatening images. A lower signal in a scanner shows that something measurable happened in these 15 or 16 brains under specific conditions. It does not show that anyone felt calmer, and a scan done two hours after dosing says nothing about day-to-day life. The study was funded partly by a South African company, and one author is a director at the extract's developer [1]. How this fits the proposed mechanism is covered in how kanna works.
What did the public-speaking study find?
It found a lower anxiety rating before the speech in one of two experiments, and nothing in the other. Reay and colleagues published both in 2020, with 20 young healthy volunteers in total, each given a single 25 mg dose of Zembrin or placebo in a double-blind, between-subject design [2].
- Experiment 1 used 20 minutes of a multitasking stressor and measured mood. There was no treatment effect.
- Experiment 2 used a 5-minute simulated public speech and measured anxiety, heart rate and skin conductance. Self-rated anxiety was significantly lower in the Zembrin group at the point before the stressor, and there was a significant treatment-by-time interaction on heart rate [2].
Read that carefully. "Lower before the stressor" is not the same as "lower during the speech." Skin conductance was also recorded, but the abstract does not report a result for it. The authors describe the result as "the first tentative behavioral evidence" and note it came from two small studies [2]. With 20 volunteers split across two experiments, each group held only a handful of people, and a sample that small can be thrown off by who happened to land in which arm.
What do the studies say about cognition and focus?
Results are narrow: two of nine cognitive domains in one trial, and one complex task in another.
Chiu 2014. Twenty-one healthy adults aged 45 to 61 took 25 mg of Zembrin or placebo daily for 3 weeks each, in a crossover with a 3-week washout. On a computerized battery (CNS Vital Signs), cognitive flexibility and executive function scored better on Zembrin than on placebo (reported P values 0.022 and 0.032; the abstract and results table list them in opposite order). Memory, verbal memory, visual memory, reaction time, complex attention, psychomotor speed and processing speed did not differ significantly, and the overall neurocognitive index was not significant [3]. Five participants dropped out, the analysis used completers, and the paper does not describe adjusting for nine tests [3]. Funding came from the extract's developer and its distributor, and one author, an HG&H director, is a trustee of a trust that holds a minor shareholding in the developer [3].
Hoffman 2020. Sixty recreationally trained adults aged 20 to 35 took 25 mg daily for 8 days and were tested two hours after the day-8 dose. Performance on a complex reactive task that required responding to repeated visual stimuli under cognitive load was better with Zembrin. Simple reaction tests, alertness and energy ratings, and total mood score did not differ [4]. The authors concluded there was an ergogenic benefit in complex reactive tasks but no mood benefit in this population [4]. We could not verify the funding.
Neither result is a general "better focus" finding. A cognitive-flexibility score and a reactive-agility task are specific things that happen to be measured in the lab.
Are there other measures, such as EEG?
Yes, one trial recorded brain waves and tests, with many exploratory comparisons. Dimpfel and colleagues gave 60 healthy adults aged 50 to 80 placebo, 25 mg or 50 mg of Zembrin daily for 6 weeks and recorded EEG at rest and during six cognitive tests [5].
The arithmetic test improved with both doses on the first day, and the number-connection test improved with 25 mg on both testing days. EEG changes were mostly specific to each test. The anxiety-rating scale (HAM-A) fell at both doses but significantly only at 50 mg (p = 0.03) [5]. The text we read does not describe correcting for the many comparisons, one author is affiliated with the developer, and the paper is in an open-access journal outside PubMed [5]. Read it as exploratory.
The four studies at a glance
| Study | People, dose | What was measured | What moved | What did not |
|---|---|---|---|---|
| Terburg 2013 [1] | 16 healthy students, 25 mg once | Amygdala activity (fMRI) | Lower amygdala response to fearful faces at low load; lower amygdala-hypothalamus coupling | High-load condition; task performance; subjective mood |
| Reay 2020 [2] | 20 young healthy volunteers, 25 mg once | Anxiety, mood, heart rate under lab stress | Lower anxiety rating before speech; heart-rate interaction (experiment 2) | Entire multitasking experiment (experiment 1) |
| Chiu 2014 [3] | 21 healthy adults, 25 mg daily, 3 weeks | Nine cognitive domains | Cognitive flexibility; executive function | Memory, attention, reaction time, processing speed, overall index |
| Hoffman 2020 [4] | 60 trained adults, 25 mg daily, 8 days | Reactive tasks, tracking, mood | Complex reactive task under cognitive load | Simple reaction, visual tracking, mood, alertness |
What are the limits of this research?
The same limits apply to every row above, and they are large.
- Healthy, mostly young or middle-aged volunteers. Nobody was selected for stress or attention problems.
- Lab stress is not life stress. A mock speech or a multitasking test is a short, controlled stand-in.
- Small samples. Twenty volunteers were split across two experiments and two arms each.
- One extract, one company's product family. All trials used Zembrin. See what Zembrin is.
- Mixed results. Each study had measures that did not move, and one of Reay's two experiments was null.
- Industry ties. Several papers were funded by, or include authors from, the extract's developer or distributor. Independent replication is the missing piece.
A 2026 review of the animal and clinical literature came to a similar conclusion: some positive signals, inconsistent results, benefits limited to specific measures such as EEG or reaction time under cognitive stress, and a need for larger trials in relevant populations [6]. For every published trial in one place, see the clinical studies table. For mood and sleep, see that post.
What is being studied next?
Two registered trials are underway or unreported as of October 29, 2026, and neither has posted results that we found. A Northumbria University trial (NCT05471804) plans 120 adults aged 30 to 50 on 25 mg or placebo for 8 weeks, with subjective stress as the primary outcome [7]. An industry-sponsored decentralized crossover (NCT07511088) plans 250 adults aged 18 to 60 who rate their anxiety after self-identified stressful episodes [8]. Until results appear, they are plans, not evidence.
Whatever those trials find, the studies used 8 to 50 mg of one extract in capsules. Drinks vary from 15 mg to 500 mg of kanna and many add other ingredients, so check the dosage guide. Anyone on serotonergic medicines or who is pregnant or nursing should talk to a doctor first; see is kanna safe.
This page is general information, not medical advice. These statements have not been evaluated by the FDA. Kanna products are not intended to diagnose, prevent or manage any condition, including stress or anxiety. kannadrinks.com is published by Psilly Goose, a kanna drink maker.
References
- Terburg D, et al. Acute effects of Sceletium tortuosum (Zembrin), a dual 5-HT reuptake and PDE4 inhibitor, in the human amygdala and its connection to the hypothalamus. Neuropsychopharmacology 2013;38(13):2708-16. PubMed Central
- Reay J, Wetherell MA, Morton E, Lillis J, Badmaev V. Sceletium tortuosum (Zembrin) ameliorates experimentally induced anxiety in healthy volunteers. Hum Psychopharmacol 2020;35(6):1-7. PubMed
- Chiu S, et al. Proof-of-concept randomized controlled study of cognition effects of the proprietary extract Sceletium tortuosum (Zembrin) targeting phosphodiesterase-4 in cognitively healthy subjects. Evid Based Complement Alternat Med 2014;2014:682014. PubMed Central
- Hoffman JR, Marcus I, Dubnov-Raz G, Gepner Y. Ergogenic effects of 8 days of Sceletium tortuosum supplementation on mood, visual tracking, and reaction in recreationally trained men and women. J Strength Cond Res 2020;34(9):2476-81. PubMed
- Dimpfel W, Gericke N, Suliman S, Chiegoua Dipah GN. Effect of Zembrin on brain electrical activity in 60 older subjects after 6 weeks of daily intake. World J Neurosci 2017;7(1):140-171. SCIRP
- de Jong M, van Niekerk S, Hamman J, van der Kooy F. Mesembryanthemum tortuosum and Zembrin: mixed evidence from in vivo animal and clinical studies on their antidepressant and anxiolytic effects. Planta Med 2026;92(8):806-823. PubMed
- ClinicalTrials.gov. NCT05471804: Psychological effects of 8 weeks supplementation with Sceletium tortuosum extract (Zembrin). ClinicalTrials.gov
- ClinicalTrials.gov. NCT07511088: A decentralized study utilizing non-invasive measures to evaluate a botanical supplement on episodes of mild acute stress and situational anxiety. ClinicalTrials.gov
Frequently asked questions
What did the kanna amygdala study find?
In 16 healthy students, a single 25 mg dose of Zembrin was followed by lower amygdala activity to fearful faces under low perceptual load, but not high load, and lower amygdala-hypothalamus coupling [1]. Task performance did not differ. It is a brain measure, not a health outcome.
Did kanna reduce anxiety in the public-speaking study?
Participants on 25 mg reported lower anxiety before a simulated speech, and heart rate showed a treatment-by-time interaction. The other experiment in the same paper, a multitasking stressor, found no effect. There were 20 young healthy volunteers in total [2].
Does kanna improve focus or memory?
The evidence is thin. One 3-week trial found better cognitive flexibility and executive function, but memory, attention, reaction time and processing speed did not differ significantly [3]. An 8-day trial found better performance on one complex reactive task but not on simple reactions [4].
Were any of these studies done in people with an anxiety disorder?
No. All participants were healthy volunteers, and the results say nothing about any condition.
Which extract and dose were tested?
Zembrin, a standardized extract, at 25 mg in nearly all cases and 50 mg in one trial. Other extracts and drinks have not been tested. See the dosage guide.