Zembrin: What It Is, What the Trials Tested and Who Paid for Them
Most human research on kanna used one branded extract. That is useful, and it comes with caveats worth knowing.
If you have read anything about kanna research, you have read about Zembrin. Nearly every published human trial of kanna used this one branded extract, which is why it keeps appearing in studies, supplements and drink labels. This post explains what it is, lays out each trial with its dose, size and ties to the extract's owner, and clarifies why "contains kanna" and "contains Zembrin" are different claims.
Zembrin is a trademarked, standardized extract of Sceletium tortuosum (kanna) developed by HG&H Pharmaceuticals [3][7]. Human studies used 8 to 25 mg of it, in small groups of healthy adults, and several were co-authored by people tied to its developer or distributor [2][7]. Results apply to Zembrin, not to every kanna product.
What is Zembrin?
Zembrin is the trade name of a standardized extract of kanna, made from a plant variety traditionally called "mak" (mild) [3].
A 2014 toxicology paper describes it as a hydroethanolic extract standardized to 0.35 to 0.45% total alkaloids, with mesembrenone and mesembrenol making up at least 60% of those alkaloids and mesembrine under 20% [3]. A 2013 safety trial calls it a "2:1 standardized extract" [5]. The extract was developed by HG&H Pharmaceuticals in South Africa; a 2013 imaging paper describes HG&H as "the company that has developed the extract" [7], and a 2014 cognition paper identifies P L Thomas as the North American distributor of Zembrin [2].
The lab pharmacology work on kanna, including its serotonin-transporter and PDE4 findings, was done with this same extract [1]. Notice the middle figure above: Zembrin is not especially high in mesembrine, the alkaloid most kanna discussion centers on. It is rich in related alkaloids. Our mesembrine explainer goes into why that matters.
Is Zembrin the same as kanna?
No. It is one extract with a specified alkaloid profile, while kanna products vary widely.
Alkaloid content in the plant differs by site, growing conditions and plant part [4][9], and traditional fermentation changes the mix: in one controlled experiment mesembrine fell from 1.33% to 0.05% as another alkaloid appeared [10]. A powder, a differently made extract or a fermented tea will not match Zembrin's profile. That does not make them worse, but it does mean the Zembrin studies cannot be used to describe them. See kanna extract and what is kanna.
What did the Zembrin trials test?
Mostly short, small studies in healthy adults, using 8 or 25 mg of the extract.
| Study | Design and people | Zembrin dose | What it measured and found |
|---|---|---|---|
| Nell 2013 [5] | Randomized, double-blind, placebo-controlled; 37 healthy adults; 3 months | 8 mg or 25 mg daily | Safety only. No apparent differences from placebo in vitals, ECG or bloodwork; headache most common and more frequent on placebo. Efficacy was not assessed. |
| Terburg 2013 [7] | Double-blind, placebo-controlled crossover fMRI; 16 healthy participants | 25 mg, single dose | Lower amygdala reactivity to fearful faces under one condition, and weaker amygdala-hypothalamus coupling. |
| Chiu 2014 [2] | Double-blind, placebo-controlled crossover; 21 healthy adults, mean age 54.6; 3 weeks each arm | 25 mg daily | Better cognitive set flexibility and executive function than placebo; authors report mood and sleep also improved; well tolerated. |
| Reay 2020 [6] | Two double-blind, placebo-controlled studies; 20 young healthy volunteers in total | 25 mg, single dose | Study 1 (multitasking stressor): no treatment effect. Study 2 (simulated public speaking): lower self-reported anxiety before the stressor and a heart-rate interaction. |
| Hoffman 2020 [11] | Randomized, placebo-controlled; 60 recreationally trained adults aged 20 to 35; 8 days | 25 mg daily | Better performance on a complex reactive task under cognitive load; no significant difference in mood or alertness scores. |
Read these as "what was measured", not as proof of any benefit. The cognition and anxiety-task results have not been replicated at scale, one of the two Reay studies found nothing, and the mood outcome in Hoffman did not move. Our research page has the fuller picture.
Who funded the Zembrin trials, and does it matter?
It matters for how much weight to give them: several trials had direct ties to the extract's developer or distributor.
- Terburg 2013: funded by H.L. Hall and Sons, Ltd, South Africa, and a Netherlands research grant. Co-author Nigel Gericke is Director of Medical and Scientific Affairs at HG&H Pharmaceuticals, "the company that has developed the extract" [7].
- Chiu 2014: financially supported by HG&H Pharmaceuticals and P L Thomas & Co. Gericke disclosed his HG&H role and a minor shareholding held through a trust. Co-author Vladimir Badmaev is listed with a P L Thomas affiliation; the disclosure says he was formerly its director of medical and scientific affairs. The paper's conflict-of-interest line states no competing financial interests [2].
- Nell 2013: Gericke is a listed author. The funding statement was not available to us, so we do not describe it [5].
- Reay 2020: Badmaev is a listed author, affiliated with American Medical Holdings Inc. We did not see the funding statement [6].
- Hoffman 2020: authors are from Israeli universities and hospitals. We did not see a funding statement [11].
- Rat toxicology (Murbach 2014): authors include staff of HG&H Pharmaceuticals and contract research laboratories [3].
Industry involvement does not make a study wrong. Many supplement ingredients are only studied because a manufacturer pays for it. It does mean the evidence base is not independent of the product being sold, and that replication by unaffiliated groups would carry extra weight. This site is also published by a kanna drink maker, which is why we state it on every page.
What is the Zembrin dose in studies versus on labels?
Studies used 8 and 25 mg of Zembrin. Labels use all sorts of numbers, and most do not name the extract.
A product that lists "25 mg kanna extract" is not necessarily Zembrin and not necessarily the same strength. Without the extract's name, ratio and alkaloid content, the number cannot be matched to the trials. As a rough illustration of scale, 25 mg of an extract specified at 0.35 to 0.45% total alkaloids [3] contains on the order of 0.09 to 0.11 mg of total alkaloids (our arithmetic from the published specification), and under about 0.02 mg of mesembrine (at most roughly 0.0225 mg) if mesembrine is below 20% of them. Check kanna dosage for how milligrams differ among drinks, and how to read a kanna label for what to look for. This post describes doses used in research; it does not recommend one.
What is known about Zembrin safety?
Limited but reassuring in the narrow settings tested, with the usual serotonergic cautions.
In the 3-month trial above, vital signs, ECG, hematology and biochemistry showed no apparent differences from placebo, and both doses were well tolerated [5]. Rat studies reported no treatment-related adverse effects, with no-observed-adverse-effect levels of 5,000 mg/kg/day for 14 days and 600 mg/kg/day for 90 days, the highest doses tested [3]. Animal results do not translate directly to people. WebMD lists headache and upset stomach as common side effects of sceletium, names SSRIs, SNRIs, MAOIs, tricyclics, antipsychotics, triptans and St. John's wort as possible interaction concerns, and says safety in pregnancy and breastfeeding is unknown [8]. Talk to a doctor if any of that applies; see is kanna safe.
What do independent reviews conclude?
That the evidence is promising but thin and inconsistent.
A 2026 critical review of animal and clinical studies of Zembrin and related products found a favorable safety profile and potential efficacy, but also small samples, studies in clinically irrelevant populations, and results that were not consistent across studies. It calls for large trials in relevant populations [12]. A 2021 review noted the plant "has not yet been studied in a clinical population" [13]. The FDA has not approved Zembrin or kanna for any condition [8].
This page is general information, not medical advice. These statements have not been evaluated by the FDA. Kanna products are not intended for any disease or health condition. kannadrinks.com is published by Psilly Goose, a kanna drink maker.
References
- Harvey AL, et al. Pharmacological actions of the South African medicinal and functional food plant Sceletium tortuosum and its principal alkaloids. J Ethnopharmacol 2011;137(3):1124-9 (study used a standardised extract, Zembrin). 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. Abstract on PubMed; affiliations, financial support and disclosure in the PMC
- 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
- Manganyi MC, et al. A chewable cure "Kanna": biological and pharmaceutical properties of Sceletium tortuosum. Molecules 2021;26(9):2557. PMC
- 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
- Reay J, et al. Sceletium tortuosum (Zembrin) ameliorates experimentally induced anxiety in healthy volunteers. Hum Psychopharmacol 2020;35(6):1-7. PubMed
- 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 (funding and disclosure section). PMC
- WebMD. Sceletium: Uses, side effects, interactions. webmd.com
- Reddy K, et al. Mass spectrometry metabolomics and feature-based molecular networking reveals population-specific chemistry in some species of the Sceletium genus. Front Nutr 2022;9:819753. PMC
- Patnala S, Kanfer I. Investigations of the phytochemical content of Sceletium tortuosum following the preparation of "Kougoed" by fermentation of plant material. J Ethnopharmacol 2009. 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
Frequently asked questions
What is Zembrin?
Zembrin is the trademarked name of a standardized Sceletium tortuosum (kanna) extract developed by HG&H Pharmaceuticals of South Africa [3][7]. A 2014 toxicology paper describes it as a hydroethanolic extract standardized to 0.35 to 0.45% total alkaloids [3].
Is Zembrin the same as kanna?
No. Zembrin is one specific extract of kanna. Plain kanna powder, other extracts and fermented preparations have different alkaloid profiles, so results from Zembrin studies do not automatically apply to them [3][4].
What dose of Zembrin was used in studies?
Human studies used 8 mg and 25 mg daily for three months in a safety trial [5], a single 25 mg dose in two lab studies [6][7], and 25 mg daily for three weeks in a cognition study [2]. These are study doses, not recommendations. See kanna dosage.
Were the Zembrin studies independent?
Partly. Several authors were employed by or tied to the extract's developer or its North American distributor, and one trial was financially supported by both [2][7]. For some trials we could not see a funding statement, and none of the trials were large. See the table in this post.
What are Zembrin's side effects?
In a three-month trial of 37 healthy adults, headache was the most common reported event and was more frequent on placebo [5]. WebMD lists headache and upset stomach as common sceletium side effects and flags interactions with serotonergic medicines [8].