Kanna
Summary
Kanna research is small and short. Four placebo-controlled studies of 16 to 60 healthy adults, all using 25 mg of the Zembrin extract, found some changes in cognitive flexibility, stress-task anxiety or brain fear responses, alongside null mood results (grade D). No trial has tested people with anxiety or depression. Most trials involved the extract's developer or distributor. A 3-month safety trial found no problems at 8–25 mg/day.
Key facts
- A succulent from South Africa whose mesembrine-type alkaloids act on serotonin reuptake and the PDE4 enzyme in lab studies[7][4]
- Cognitive flexibility (D), anxiety during a lab stress task (D), amygdala fear response on fMRI (D), complex reaction time (D)[2][3][4][5]
- None set; kanna is a herb, not a nutrient[6]
- None studied in people; a theoretical serotonin-excess risk with antidepressants follows from its mechanism[7]
- A 3-month placebo-controlled trial in 37 healthy adults found no changes in vital signs, ECG or blood tests[1]
- 4 graded human outcomes on this page
- October 10, 2026
How it works
ProposedMesembrine, the best-known kanna alkaloid, blocks the serotonin transporter in binding assays, more potently than fluoxetine, and the Zembrin extract also inhibits the PDE4 enzyme. In one fMRI study a single 25 mg dose dampened amygdala reactivity to fearful faces. How these lab actions translate into mood effects in people is not established.[7][4]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Cognition | Grade D | Mixed | RCT · n = 60 · 2020 | 2 rows |
| Stress | Grade D | Mixed | RCT · n = 20 · 2020 | 2 rows |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Reaction performance, alertness and mood | Mixed | Grade D | RCT · n = 60 · 2020 Recreationally trained men and women aged 20–35 (Israel) Form: Sceletium tortuosum extract · Dose: 25 mg/day · Duration: 8 days Complex reactive performance under cognitive load improved versus placebo, but alertness, energy, total mood score and simple reaction time did not change. | 32740286 (opens PubMed)Source [5] |
| Cognitive set flexibility and executive function | Improved | Grade D | Crossover RCT · n = 21 · 2014 Cognitively healthy adults (mean age 55, Canada) Form: Zembrin standardized extract · Dose: 25 mg/day · Duration: 3 weeks per arm Cognitive set flexibility (p<0.032) and executive function (p<0.022) improved versus placebo; positive changes in mood and sleep were reported. Well tolerated. | 25389443 (opens PubMed)Source [2] |
| Anxiety and mood during laboratory stress tasks | Mixed | Grade D | RCT · n = 20 · 2020 Young healthy volunteers (UK) Form: Zembrin standardized extract · Dose: 25 mg, single dose · Duration: Single dose No treatment effect in the multitasking study. In the public-speaking study, subjective anxiety was lower before the stressor and heart rate response differed versus placebo. | 32761980 (opens PubMed)Source [3] |
| Amygdala reactivity to fearful faces (fMRI) | Improved | Grade D | Crossover RCT · n = 16 · 2013 Healthy adults (Netherlands) Form: Zembrin standardized extract · Dose: 25 mg, single dose · Duration: Single dose Amygdala reactivity to fearful faces under low perceptual load was reduced, and amygdala–hypothalamus coupling fell during emotion matching. | 23903032 (opens PubMed)Source [4] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Zembrin (standardized 2:1 hydroethanolic extract) | Varies[8] | No human pharmacokinetic data in our sources.[8] | Well tolerated at 8 and 25 mg/day for 3 months; rat studies found no adverse effects up to the highest doses tested.[1][8] | All human trials cited here (8–25 mg/day) |
| Dried or fermented kanna plant (traditional; chewed, brewed, snuffed or smoked) | Varies[9][6] | Alkaloid content varies widely by plant and preparation.[9] | No controlled human safety data.[6] | Not tested in controlled trials |
Studied doses
Doses studied in human trials ranged from 8 to 25 mg/day of the Zembrin extract, from a single dose to 3 months; every efficacy study used 25 mg. Results do not transfer to raw plant material or other extracts, whose alkaloid content differs.[1][2][3][5]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Medicines
- Antidepressants and other serotonergic drugsReviewNo human interaction studies. Because mesembrine blocks serotonin reuptake in lab assays, combining kanna with these drugs carries a theoretical risk of excess serotonin. Do not combine without your prescriber.[7]
- PDE4 inhibitorsReviewThe Zembrin extract inhibits PDE4 in lab work; additive effects are theoretical and unstudied.[4]
Who should be careful
- Taking antidepressants
- Kanna acts on the same serotonin transporter as SSRIs in lab assays; no safety data exist for the combination.[7]
- Depression or anxiety disorders
- No trial has tested kanna in people with these conditions; a 2026 review calls for trials in relevant populations.[6]
- Pregnancy and breastfeeding
- No human safety data.[6]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Safety
Short-term safety data are reassuring but come from small, industry-linked studies of one extract.
- 3-month trial
- At 8 and 25 mg/day for 3 months, vital signs, ECG and blood tests did not differ from placebo; headache, stomach pain and colds were more common on placebo.[1]
- Animal toxicology
- In rats, a 90-day study found no treatment-related adverse effects up to 600 mg/kg/day, the highest dose tested.[8]
- Serotonin
- Mesembrine's serotonin-reuptake action is the basis for caution with antidepressants.[7]
How to read the label
- Label dose vs clinical doseTrials used 25 mg/day of Zembrin (8 mg in one safety arm). Products listing hundreds of milligrams of "kanna powder" or a different extract are not comparable.[1][2][8]
- Check the extractZembrin is standardized to 0.35–0.45% total alkaloids, mostly mesembrenone and mesembrenol; other extracts may be standardized to mesembrine instead.[8]
- Name changesKanna may be labeled Sceletium tortuosum or Mesembryanthemum tortuosum; they are the same plant.[6]
Cost per studied dose, without the sales pitch
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Cost per studied dose
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Frequently asked questions
Does kanna help with anxiety?
Only lab-stress data in healthy people: one single-dose study found lower anxiety before a speaking task, and another found no effect. No trial has tested anxiety disorders.[3][6]
Does kanna improve focus?
A 21-person, 3-week crossover trial found better cognitive flexibility, and an athlete study found faster complex reactions but no mood change. Both were small.[2][5]
How much kanna is used in studies?
25 mg/day of the Zembrin extract in every efficacy trial; 8 mg/day was also tested for safety.[1][2][3][5]
Can I take kanna with an SSRI?
Not without your prescriber. Kanna's main alkaloid blocks serotonin reuptake in lab assays, and the combination has never been studied.[7]
Is kanna safe?
A 3-month trial at 8–25 mg/day found no safety signals in 37 healthy adults. Longer use and use with medications are unstudied.[1]
Sources
- [1]A randomized, double-blind, parallel-group, placebo-controlled trial of Extract Sceletium tortuosum (Zembrin) in healthy adults.. J Altern Complement Med, 2013. RCT
- [2]Proof-of-Concept Randomized Controlled Study of Cognition Effects of the Proprietary Extract Sceletium tortuosum (Zembrin) Targeting Phosphodiesterase-4 in Cognitively Healthy Subjects: Implications for Alzheimer's Dementia.. Evid Based Complement Alternat Med, 2014. crossover-RCT
- [3]Sceletium tortuosum (Zembrin(®) ) ameliorates experimentally induced anxiety in healthy volunteers.. Hum Psychopharmacol, 2020. RCT
- [4]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. crossover-RCT
- [5]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. RCT
- [6]Mesembryanthemum tortuosum and Zembrin: Mixed Evidence from In vivo Animal and Clinical Studies on their Antidepressant and Anxiolytic Effects.. Planta Med, 2026. review
- [7]Mesembrine: The archetypal psycho-active Sceletium alkaloid.. Phytochemistry, 2019. review
- [8]A toxicological safety assessment of a standardized extract of Sceletium tortuosum (Zembrin®) in rats.. Food Chem Toxicol, 2014. animal-study
- [9]A Chewable Cure "Kanna": Biological and Pharmaceutical Properties of Sceletium tortuosum.. Molecules, 2021. review
What changed
- First draft. Every PMID checked against NCBI E-utilities esummary (title and year taken from the record) and abstracts read for the cited rows.
- Adversarial review pass: every evidence row re-read against its PubMed abstract. Industry ties taken from PMC4217361 (HG&H and PL Thomas funding; Gericke and Badmaev roles) and PMC3828542 (H.L. Hall and Sons funding; Gericke role). The 3-month safety RCT (PMID 23441963) measured no efficacy outcomes, so it appears in safety, not as an evidence row. No NIH ODS, NCCIH or LPI page exists for kanna; the page relies on trials and a 2026 conflict-free review. Retraction, expression-of-concern and erratum check run on all 9 PMIDs: none flagged (an erratum on a different review, PMID 34333104, kept that review out of the sources). Page set indexable.