Kanna Benefits: What the Research Actually Shows
Five human studies, one standardized extract, small groups of healthy people. Here is what they found and what they cannot tell you.
Kanna benefits have been studied in six small human trials, all using one branded extract, Zembrin, at 8 to 50 mg. They report effects on amygdala activity, some cognitive tests and, in one study, self-reported anxiety during a stress task. Participants were healthy, sample sizes were small, and several authors are linked to the extract's owner. The evidence is promising but preliminary.
What do the human studies on kanna show?
Six published human studies are the core of the evidence on kanna benefits. Each tested Zembrin, a standardized extract of Sceletium tortuosum, in healthy volunteers, at doses from 8 mg to 50 mg. If you want background on the plant first, start with What Is Kanna?
A word on language. The studies measured things: brain scans, test scores, heart rate, ratings people gave themselves. We report what was measured and what happened. None of these studies tested kanna in people with a medical condition, and none shows that kanna or any product containing it helps with one.
Here is each study in a little more detail before the table.
- Terburg 2013. A brain imaging study. After a single 25 mg dose, amygdala reactivity to fearful faces was lower (in the low perceptual load condition), and coupling between the amygdala and hypothalamus was reduced [1].
- Chiu 2014. A three-week cognition trial. Zembrin at 25 mg per day improved cognitive set flexibility (P < 0.032) and executive function (P < 0.022) versus placebo. The authors also reported positive changes in mood and sleep [2].
- Reay 2020. Two small experiments. In the first, which used a multitasking stressor, there was no treatment effect. In the second, a simulated public-speaking task, a single 25 mg dose was associated with lower subjective anxiety beforehand and a significant treatment-by-time effect on heart rate [3].
- Nell 2013. A three-month safety and tolerability trial at 8 mg or 25 mg a day. There were no differences in vital signs, ECG or bloodwork, and headache was the most common adverse event, more often in the placebo group. Efficacy was not assessed [4].
- Hoffman 2020. Eight days of 25 mg in recreationally trained adults. Performance on a complex reactive task under cognitive load improved. Mood scores and alertness ratings did not change [5].
Study-by-study table
| Study | People | Dose | Duration | What they measured | Result | Limits |
|---|---|---|---|---|---|---|
| Terburg et al. 2013 [1] | 16 healthy participants | 25 mg Zembrin | Single dose | Brain activity (fMRI) while viewing fearful faces | Lower amygdala reactivity (low perceptual load) and reduced amygdala-hypothalamus coupling vs placebo | Small; brain measure, not a health outcome; one extract |
| Chiu et al. 2014 [2] | 21 healthy adults, mean age 54.6 | 25 mg/day Zembrin | 3 weeks (crossover) | Cognitive tests, mood, sleep | Better cognitive set flexibility and executive function vs placebo; positive changes in mood and sleep reported; well tolerated | Small; healthy adults; one extract; authors linked to the extract's owner |
| Reay et al. 2020 [3] | 20 young healthy volunteers across two studies | 25 mg Zembrin | Single dose | Self-rated anxiety and heart rate during stressors | Study 1 (multitasking): no effect. Study 2 (public speaking): lower anxiety before the stressor and a heart-rate interaction | Very small; one of two studies null; short-term; authors call the evidence "tentative"; authors linked to the extract's owner |
| Nell et al. 2013 [4] | 37 healthy adults | 8 mg or 25 mg/day Zembrin | 3 months | Safety: vital signs, ECG, bloodwork, adverse events | No differences from placebo; headache most common and more frequent on placebo | Efficacy not assessed; healthy adults; authors linked to the extract's owner |
| Hoffman et al. 2020 [5] | 60 recreationally trained adults | 25 mg Zembrin | 8 days | Reaction and visual tracking under cognitive load; mood and alertness ratings | Better complex reactive task performance under load; no change in mood score or alertness | Short; fit, active adults; one extract; some measures did not move |
| Dimpfel et al. 2017 [10] | 60 adults aged 50 to 80 | 25 or 50 mg/day Zembrin | 6 weeks (parallel, 3 arms) | EEG, cognitive tests, anxiety (HAM-A), mood (POMS) | Some EEG and cognitive-test changes; HAM-A anxiety score fell with 50 mg (p = 0.03); most mood changes not significant | Small groups; many outcomes; co-author from the Zembrin developer; authors call some findings tentative |
All doses are of Zembrin, a standardized extract. Author-affiliation notes come from the PubMed records, which list HG&H Pharmaceuticals or a related company for Nell, Chiu and Reay.
What are the plain-English takeaways?
Zembrin at 25 mg has been associated with measurable changes in a few lab-style outcomes in healthy people. That is a long way from showing that anyone will feel better.
Taking the studies together:
- Something measurable happens in the brain. The Terburg scan fits with the lab finding that kanna alkaloids act on the serotonin transporter and PDE4. The mechanism itself is still debated, as covered in our explainer.
- Cognition results are tentative. One three-week trial found better set flexibility and executive function. Another found a task-specific improvement under load. Neither is a broad "sharper thinking" result.
- Mood and anxiety findings are mixed. Chiu reported positive changes in mood and sleep. Reay found lower self-reported anxiety in one stress task and nothing in the other. Hoffman found no change in mood or alertness ratings.
- Short-term tolerability looked fine in healthy adults. The three-month trial found no differences in vital signs, ECG or bloodwork against placebo [4]. That says little about people taking medication or about long-term use at other doses.
It is worth noticing what is missing. There are no trials in people with a diagnosed condition, none on drinks, and none comparing Zembrin with other kanna extracts. Replication by researchers with no tie to the extract's owner would make the picture much clearer.
How good is the evidence for kanna?
Independent reviewers describe it as promising but limited. A 2026 critical review of animal and clinical studies found a favourable safety profile and potential efficacy, but called the evidence mixed and pointed to small sample sizes [6]. A 2021 review of the plant's chemistry and pharmacology noted that Sceletium tortuosum has not yet been studied in a clinical population, meaning patients, and that findings come from healthy volunteers and animals [7].
Put the weaknesses side by side:
- Small samples. The largest study had 60 people. Most had 16 to 37.
- Healthy volunteers. Results may not carry over to anyone else.
- One extract. Every trial here used Zembrin. Findings do not automatically apply to other extracts or products.
- Short durations. Single doses to three months.
- Mixed outcomes. Some measures improved, some did not, and one of Reay's two studies was null.
Animal safety work exists as well. In rats, a toxicology assessment of Zembrin set no-observed-adverse-effect levels at 5,000 mg/kg/day in an acute study and 600 mg/kg/day in a 90-day study [8]. Animal data do not translate directly to people, but they are part of why researchers describe the safety picture as favourable.
Who paid for the research?
Several of the Zembrin trials list authors from HG&H Pharmaceuticals, the company that owns Zembrin, or related companies. In the PubMed records for Nell, Chiu and Reay, author affiliations show HG&H or American Medical Holdings.
That is common in supplement research and it does not mean the results are wrong. Companies often fund the only trials that get done on a proprietary ingredient. It does mean the findings deserve extra caution until independent groups repeat them. We did not review funding statements for Terburg 2013 or Hoffman 2020 beyond what appears in the PubMed records, so we make no claim either way for those two.
We also disclose our own position. This site is published by Psilly Goose, which makes a kanna drink. We've kept product recommendations off the study summaries for that reason, and our ranking is on a separate page.
What does this mean for kanna drinks?
Not much directly, because the doses and extracts in drinks differ from what was studied. Every human trial used Zembrin, at 8 mg to 50 mg per day. Canned drinks on the market list anywhere from 15 mg to 500 mg of kanna, and only some name the extract.
Three practical points:
- Dose. A can with 15 mg is below the 25 mg most trials used. A can with 500 mg of an unnamed extract has no matching clinical data. Our dosage guide lists what each brand states.
- Extract. Milligrams of one extract are not comparable with milligrams of another. Some cans, including Silly, do not state the extract's standardization on the label.
- Everything else in the can. Many kanna drinks also contain kava, caffeine, L-theanine or lion's mane. The Zembrin studies say nothing about those combinations.
In short, the trials are a reason to be curious about kanna, not evidence that a particular drink does anything.
What about safety?
Talk to a doctor or pharmacist before using kanna if you take any serotonergic medicine, and avoid it if you are pregnant or nursing unless a clinician advises otherwise. Interaction concerns have been raised with MAOIs, SSRIs, SNRIs, tricyclic antidepressants, antipsychotics, triptans and St. John's wort, and the interactions are not fully understood. There are no data on pregnancy or breastfeeding, and the FDA has not reviewed sceletium for safety and effectiveness [9]. Our safety guide goes deeper.
These statements have not been evaluated by the FDA. Kanna products are not intended for the diagnosis, prevention or management of any disease.
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
- 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
- Reay J et al. Sceletium tortuosum (Zembrin) ameliorates experimentally induced anxiety in healthy volunteers. Hum Psychopharmacol 2020;35(6):1-7. PubMed
- Nell H et al. A randomized, double-blind, parallel-group, placebo-controlled trial of extract Sceletium tortuosum (Zembrin) in healthy adults. J Altern Complement Med 2013;19(11):898-904. PubMed
- Hoffman JR et al. 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
- de Jong M et al. 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
- Olatunji TL et al. Sceletium tortuosum: a review on its phytochemistry, pharmacokinetics, biological and clinical activities. J Ethnopharmacol 2021;280:114476. PubMed
- Murbach TS et al. A toxicological safety assessment of a standardized extract of Sceletium tortuosum (Zembrin) in rats. Food Chem Toxicol 2014;74:190-9. PubMed
- WebMD. Sceletium: uses, side effects, interactions. WebMD
- 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: a prospective, randomized, double-blind, placebo-controlled, 3-armed study in a parallel design. World J Neurosci 2017;7(1):140-171. SCIRP
Frequently asked questions
What are the benefits of kanna?
Small human studies of a standardized extract called Zembrin have reported effects on brain activity, some cognitive tests and, in one study, self-reported anxiety during a stress task. The studies are small, in healthy people, and several have industry-linked authors, so they are not proof of a health benefit.
Has kanna been proven to help anxiety or depression?
No. The published human studies were in healthy volunteers, not patients. A 2021 review noted the plant has not yet been studied in a clinical population, and a 2026 review described the evidence as mixed.
Do kanna drinks work like the studied extract?
Not necessarily. Nearly all human trials used Zembrin at 8 mg or 25 mg. Drinks use different extracts at doses from 15 mg to 500 mg, so the results do not transfer directly. See the dosage guide.
Is kanna safe?
Short trials in healthy adults reported few side effects, mainly headache. Kanna may interact with serotonergic medicines, and there are no pregnancy data. See Is Kanna Safe?
Who funded the kanna research?
Author affiliations on several trials, including Nell 2013, Chiu 2014 and Reay 2020, list HG&H Pharmaceuticals (Zembrin's owner) or a related company. That does not invalidate the findings, but readers should know it.