Kanna (Sceletium Tortuosum): Benefits, Side Effects, Dosage And Safety

Kanna is the common name for Sceletium tortuosum, a South African succulent that has been chewed, fermented and used as a mood-lifting plant for centuries. Its main alkaloids, especially mesembrine, block the serotonin transporter and inhibit the enzyme PDE4 in lab tests. A small number of human trials of a standardized extract called Zembrin (8–25 mg a day) suggest modest effects on stress reactivity and some measures of thinking, but the research is thin, and kanna should not be mixed with SSRIs, MAOIs or other serotonergic drugs.

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What Is Kanna?

Kanna is a low-growing succulent native to the Western and Northern Cape of South Africa. Its botanical name is Sceletium tortuosum, and you will also see it sold as “sceletium,” “kougoed” or simply “kanna herb.” Traditional preparations involved chewing or fermenting the plant material, which is why one recent review calls it “a chewable cure.”^[2]

Today kanna is sold as dried powder, tinctures, capsules and concentrated extracts. The form with by far the most research behind it is Zembrin, a standardized 2:1 extract that was used in every human trial described on this page.^[3]

How Kanna Works: Mesembrine, Serotonin And PDE4

Kanna’s activity is attributed mainly to a group of alkaloids: mesembrine, mesembrenone and mesembrenol. In a 2011 lab study, a standardized ethanolic extract of the plant was a potent blocker of the serotonin (5-HT) transporter and also inhibited phosphodiesterase-4 (PDE4), without affecting other phosphodiesterases. Mesembrine was the most potent alkaloid at the serotonin transporter, while mesembrenone was active against both the transporter and PDE4.^[1]

Those two actions explain both the interest and the caution:

• Serotonin reuptake inhibition is the same basic mechanism used by SSRI antidepressants. It is why kanna is studied for mood and anxiety, and why it should not be stacked with serotonergic medications.
• PDE4 inhibition raises cyclic AMP inside cells, a pathway linked to memory and alertness. This is the rationale for testing Zembrin on cognition.^[4]

Keep in mind that these mechanisms were measured in test tubes. How strongly a 25 mg oral dose engages them in the human brain is not well established.

Kanna Benefits: What The Research Shows

The human evidence base for kanna consists of a handful of small, mostly industry-linked studies of Zembrin in healthy volunteers. There are no large trials and no studies in people with diagnosed anxiety or depression.^[8]

Stress And Anxiety Reactivity (Evidence: Limited)

In a double-blind, placebo-controlled crossover fMRI study, 16 healthy volunteers took a single 25 mg dose of Zembrin. Compared with placebo, the extract reduced amygdala reactivity to fearful faces under low perceptual load and reduced coupling between the amygdala and hypothalamus during an emotion-matching task. The authors described this as the first evidence that the extract dampens the brain’s threat circuitry.^[5]

A separate double-blind study in 20 healthy young adults found that a single 25 mg dose reduced anticipatory anxiety before a simulated public-speaking task, but it had no anxiety-lowering or cognitive effect during a multitasking stress test.^[6][8]

Brain-imaging changes and one lab stress test are a reasonable start, but they do not show that kanna relieves real-world anxiety.

Cognitive Flexibility And Executive Function (Evidence: Limited)

In a randomized, placebo-controlled crossover trial, 21 cognitively healthy adults aged 45 to 65 took 25 mg of Zembrin daily for three weeks. Zembrin improved cognitive set flexibility and executive function compared with placebo, but it did not change the overall composite score across the nine-test battery.^[4][8]

In 60 recreationally trained adults aged 20 to 35, eight days of 25 mg Zembrin improved performance on complex reaction tasks that carried a cognitive load. It did not change simple reaction time, self-rated alertness and energy, or total mood scores compared with placebo.^[7] The analysis was not corrected for multiple comparisons, which raises the chance of false-positive findings.^[8]

Mood, Well-Being And Sleep (Evidence: Preliminary)

Kanna’s reputation as a mood lifter comes mostly from traditional use and anecdote. In the three-month safety trial, some participants taking Zembrin wrote unsolicited diary notes about better stress coping and sleep, but well-being was not a measured outcome.^[3] In the three-week cognition trial, Zembrin did not change depression scores, though participants reported better subjective sleep quality.^[8]

Study	Participants	Zembrin Dose	Main Finding
Nell et al., 2013	37 healthy adults	8 or 25 mg/day for 3 months	Safety study; well tolerated, no lab or ECG changes
Terburg et al., 2013	16 healthy adults	25 mg, single dose	Lower amygdala reactivity to fearful faces (fMRI)
Chiu et al., 2014	21 adults aged 45–65	25 mg/day for 3 weeks	Better cognitive flexibility and executive function
Hoffman et al., 2020	60 active adults	25 mg/day for 8 days	Better complex reaction performance under cognitive load
Reay et al., 2020	20 young adults	25 mg, single dose	Less anticipatory anxiety before a speaking task

Kanna Dosage: What Doses Were Studied?

The only doses with controlled human data are for the Zembrin extract. The most common dose is 25 mg taken once a day.^[8]

Purpose	Dose	Duration	Study
Safety and tolerability	8 mg or 25 mg Zembrin daily	3 months	Nell 2013[3]
Executive function	25 mg Zembrin daily	3 weeks	Chiu 2014[4]
Reaction performance under load	25 mg Zembrin daily	8 days	Hoffman 2020[7]
Threat reactivity / anticipatory anxiety	25 mg Zembrin	Single dose	Terburg 2013; Reay 2020[5][6]

There is no validated kanna extract dosage for raw powder, tinctures or high-concentration “10x” or “20x” extracts, because those products have not been tested in controlled trials. Alkaloid content varies a lot between plant material and processing methods, so a gram of one powder is not equivalent to a gram of another. If you use kanna at all, a standardized extract at the studied 25 mg dose is the only option with published safety data.

Kanna Extract Vs Powder: Forms And What To Look For

• Standardized extract (Zembrin): A 2:1 extract standardized for its alkaloids and the form used in every trial above.^[3] If a label names Zembrin, you know which research it maps to.
• Generic kanna extract powder: Often sold by a ratio (10:1, 20:1) without a stated alkaloid percentage. A ratio tells you how much plant went in, not how much mesembrine came out.
• Dried kanna powder or “kanna herb”: Closest to traditional use, but alkaloid content is unpredictable and there are no dosing studies.
• Kanna tincture and capsules: Convenience formats. Judge them by what extract they contain and whether total alkaloids are listed.

Whatever the form, look for a certificate of analysis that shows alkaloid content and screening for contaminants. Reviews of the plant note real concerns about quality, standardization and authenticity across botanical products.^[2]

Is Kanna Safe? Kanna Side Effects

For the Zembrin extract in healthy adults, the short-term safety record is reassuring. In the three-month randomized trial, 8 mg and 25 mg daily doses caused no meaningful changes in vital signs, ECG, body weight, blood counts or blood chemistry. Headache was the most common adverse event, followed by abdominal pain and upper respiratory infections, and each was more frequent in the placebo group than in the kanna groups.^[3]

Side effects reported in kanna trials include:^[8]

• Headache
• Mild stomach discomfort or abdominal pain
• Constipation, decreased appetite, insomnia and irritability (rated “possibly” related in a few participants)

Important limits on that safety picture:

• Safety has not been established beyond three months of use.^[8]
• The data apply to low-dose standardized extract, not to large doses of raw powder, concentrated extracts or smoked or snorted products.
• No trials have included pregnant or breastfeeding women, children or people with psychiatric diagnoses.

Drug Interactions: Do Not Mix Kanna With SSRIs, MAOIs Or Serotonergic Drugs

This is the most important safety point on this page. Because kanna’s alkaloids inhibit the serotonin transporter, kanna should not be used with drugs that alter serotonin uptake or release, including SSRIs and SNRIs.^[8] That warning is based on mechanism rather than documented case reports, but the risk it guards against is serious.

Combining two or more serotonin-raising drugs can trigger serotonin syndrome, a potentially life-threatening reaction. Symptoms can appear within minutes to hours and include agitation, fast heartbeat, high blood pressure, fever, loss of coordination, overactive reflexes, nausea, vomiting and diarrhea. Older antidepressants called MAOIs can also trigger it when combined with other serotonergic drugs. Untreated, serotonin syndrome can be fatal.^[9]

Avoid kanna, or use it only under a doctor’s direction, if you take or recently stopped:

• SSRIs or SNRIs (for example, sertraline, fluoxetine, escitalopram, venlafaxine)
• MAOIs, including some older antidepressants
• Triptans for migraine, tramadol, meperidine, fentanyl or dextromethorphan^[9]
• Recreational drugs such as MDMA, amphetamines or LSD^[9]
• Prescription PDE4 inhibitors such as roflumilast^[8]

Also avoid kanna if you are pregnant or nursing, have bipolar disorder, or are being treated for depression, unless your prescriber approves it. Do not use kanna to replace or taper off an antidepressant.

How Kanna Pairs With Other Nootropics

No studies have tested kanna in combination with other supplements, so any stack is guesswork. If you are healthy, take no serotonergic medications and want to experiment, a cautious approach is to keep stacks simple:

• L-theanine is a common, well-tolerated pairing for calm focus and does not act on the serotonin transporter.
• Avoid stacking kanna with other mood-active botanicals such as saffron until you know how you respond to each one alone, since their combined effects are untested.
• If stress is your main goal, adaptogens like Rhodiola rosea and ashwagandha have larger research bases. See our adaptogens guide.

For an overview of combinations that are better studied, see our guide to nootropic stacks and our page on nootropic side effects.

Where To Buy Kanna

If you decide to try kanna, choose a single-ingredient product that names its extract (ideally Zembrin) and lists alkaloid content, and avoid blends that hide the dose in a proprietary formula. For third-party-tested single ingredients, we generally point readers to Nootropics Depot. On Amazon, buy only from listings marked “Sold by Nootropics Depot.”

Check Nootropics Depot Kanna Options

If you would rather avoid serotonergic botanicals altogether, browse our ingredient library or our roundup of the best nootropics for options with a deeper evidence base.

Kanna FAQs

What Is Kanna Used For?

Traditionally, kanna was chewed or fermented as a mood-lifting plant.^[2] Today it is marketed for stress, mood and focus. The best human evidence is for short-term changes in threat reactivity and some executive function measures with 25 mg of Zembrin, and it remains limited.^[4][5]

Does Kanna Get You High?

The controlled trials used 8–25 mg of standardized extract and reported mild adverse events such as headache; they were not designed to study intoxication.^[3] Reports of a “kanna high” come from online anecdotes about much larger or concentrated doses, which have no safety data. We do not recommend using kanna recreationally.

How Long Does Kanna Last?

We could not find published human pharmacokinetic studies that define how long kanna’s effects last. In the single-dose studies, effects were measured within a few hours of a 25 mg dose, and in one trial testing took place two hours after the last dose.^[7]

Can You Take Kanna With An SSRI?

No. Kanna inhibits the serotonin transporter, and it should not be combined with SSRIs, SNRIs or other serotonergic drugs because of the risk of serotonin syndrome.^[8][9] Talk with your prescriber before using any mood-active supplement.

Is Kanna A Nootropic?

Loosely, yes. It is marketed as one, and two small trials found improvements in cognitive flexibility and reaction performance under cognitive load.^[4][7] Its evidence is weaker than that of better-studied ingredients covered in our what are nootropics guide.

How Much Kanna Should I Take?

The studied dose is 25 mg of the Zembrin extract once daily, with 8 mg also tested for safety.^[3] There are no evidence-based doses for raw powder or unstandardized extracts.

References

1. Harvey AL, Young LC, Viljoen AM, Gericke NP. Pharmacological actions of the South African medicinal and functional food plant Sceletium tortuosum and its principal alkaloids. Journal of Ethnopharmacology. 2011;137(3):1124-1129. DOI
2. Manganyi MC, Bezuidenhout CC, Regnier T, Ateba CN. A chewable cure “kanna”: biological and pharmaceutical properties of Sceletium tortuosum. Molecules. 2021;26(9):2557. DOI
3. Nell H, Siebert M, Chellan P, Gericke N. A randomized, double-blind, parallel-group, placebo-controlled trial of extract Sceletium tortuosum (Zembrin) in healthy adults. Journal of Alternative and Complementary Medicine. 2013;19(11):898-904. DOI
4. Chiu S, Gericke N, 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: implications for Alzheimer’s dementia. Evidence-Based Complementary and Alternative Medicine. 2014. PMC
5. Terburg D, Syal S, Rosenberger LA, 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). DOI
6. Reay J, Wetherell M, Morton E, Lillis J, Badmaev V. Sceletium tortuosum (Zembrin) ameliorates experimentally induced anxiety in healthy volunteers. Human Psychopharmacology: Clinical and Experimental. 2020. DOI
7. Hoffman JR, Markus 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. Journal of Strength and Conditioning Research. 2020;34(9):2476-2481. PubMed
8. Alzheimer’s Drug Discovery Foundation. Sceletium tortuosum (supplement). Cognitive Vitality report. ADDF Cognitive Vitality
9. MedlinePlus Medical Encyclopedia. Serotonin syndrome. U.S. National Library of Medicine. MedlinePlus