Kanna Tolerance: Reports vs. Evidence
Online forums are full of claims about tolerance, reverse tolerance and tolerance breaks. The research has not tested any of them.
Kanna tolerance is one of those topics where the internet is confident and the research is silent. Forum threads describe needing more over time, needing less over time, taking breaks, and "resetting." That is a lot of detail for something no study has measured. This post separates what people report from what trials show, and says plainly where the evidence stops.
No clinical study has measured tolerance to kanna. The longest human trial gave 37 healthy adults 8 mg or 25 mg of one extract daily for 3 months and assessed safety and tolerability, not tolerance [1]. Claims about building tolerance, reverse tolerance or tolerance breaks come from anecdote. They may be true for some people, but they are untested.
What does tolerance mean, and how is it different from tolerability?
Tolerance means the body adapts so that more of a substance is needed to get the same effect.
NIDA's research guide describes it this way: the body adapts to a drug, "requiring more of it to achieve a certain effect (tolerance)," and produces drug-specific physical or mental symptoms if use stops abruptly (withdrawal). NIDA adds that physical dependence of this kind can occur with many drugs, including prescription medicines taken as directed, and does not by itself constitute addiction [4]. We cover that distinction in is kanna addictive.
Tolerance is easily confused with tolerability, which is a clinical-trial term for how well participants cope with a treatment: side effects, dropouts, lab values. A study can report that a product was "well tolerated" and say nothing about whether the effect fades over time. That is exactly the situation with kanna.
What did the human trials cover?
Single doses, up to 3 weeks of daily use, and one 3-month safety trial, none designed to test for tolerance.
| Study | Who | Dose and length | What it measured |
|---|---|---|---|
| Dimpfel 2017 [12] | 60 healthy adults aged 50 to 80 | 25 mg or 50 mg daily for 6 weeks | EEG, cognitive tests, mood, sleep questionnaire |
| Terburg 2013 [5] | 16 healthy adults | One 25 mg dose | Brain-imaging response to fearful faces |
| Reay 2020 [6] | 20 healthy volunteers across two studies | One 25 mg dose | Anxiety and heart rate during lab stress tasks |
| Hoffman 2020 [3] | 60 recreationally trained adults | 25 mg daily for 8 days | Reaction tasks, mood, alertness |
| Chiu 2014 [2] | 21 adults, mean age 54.6 | 25 mg daily for 3 weeks, then a 3-week washout and crossover | Cognition, mood, adverse events |
| Nell 2013 [1] | 37 healthy adults | 8 mg or 25 mg daily for 3 months | Safety: vitals, ECG, bloodwork, adverse events |
Look at what is absent. In the Nell trial, no efficacy variables were assessed at all [1], so it could not show whether an effect faded. The studies that did measure effects mostly measured them once, after a single dose or at the end of a short course [3][5][6]. The Chiu cognition study measured over 3 weeks but with only a single dose level [2]. No trial we found compared early and late responses, tested higher doses after weeks of use, or asked whether participants needed more over time. A 2026 critical review of the animal and clinical evidence similarly stresses small samples and mixed results [7].
That the 3-month trial found no differences in vital signs, ECG or bloodwork versus placebo, and called both doses well tolerated [1], is useful safety information. It is not tolerance data. For funding and conflict notes, several of these trials involved authors affiliated with the extract's owner, and most used the same standardized extract, Zembrin [1][2][5][6].
Is there animal or lab evidence on tolerance?
Not on tolerance specifically, as far as we found.
Animal work on Sceletium has looked at other things. A 2014 rat study used standard behavioral tests, including conditioned place preference, a test used to model abuse liability, and reported that a Sceletium extract did not cause preference or aversion [8]. A conditioned place preference test is not a tolerance test, and a rat result may not carry over to people. The lab studies that describe kanna's mechanism measured how an extract affects the serotonin transporter and the enzyme PDE4 in a dish [9]. Those findings do not tell you what happens with repeated use in a person.
A 2021 review of the plant's chemistry, pharmacokinetics and clinical activities describes the clinical evidence as coming from healthy volunteers and notes that the plant had not yet been studied in a clinical population [10]. In plain terms, the question you are asking has not been put to the plant.
What do people report, and how much should that count?
User reports can point to questions worth studying, but they cannot answer them.
Online communities contain accounts of kanna "wearing off" with daily use, of effects seeming stronger after a break, and of the opposite. We do not cite those accounts because they cannot be checked. People differ in the product they take, how much it contains, what else they use, how much they sleep, and what they expect. Expectation alone can change how a drink feels. Products also vary: dose and extract differ widely between brands, which is why milligrams on one label are not comparable to another [11]. A person who changed brands may attribute the change to tolerance.
Two opposite reports can both be real for different people, and neither tells you what is typical. That is what controlled studies are for, and none exist here.
Can you take kanna every day?
One 3-month trial found daily use of one extract well tolerated in healthy adults; beyond that, the evidence runs out.
That trial used 8 mg or 25 mg once daily, with 12, 12 and 13 people in the three groups [1]. It was small, limited to healthy adults, and used one extract, so it cannot establish what happens at other doses, in other populations, over longer periods, or with products with different alkaloid content. We also cannot say how often is "too often." We do not recommend a schedule, because we cannot support one. A clinician is the right person to ask, particularly if you take a medicine that affects serotonin; WebMD lists SSRIs, SNRIs, MAOIs, tricyclics, antipsychotics, triptans and St. John's wort as interaction concerns for sceletium [11]. See kanna and drug interactions, is kanna safe and kanna dosage.
What about redosing, tolerance breaks and reverse tolerance?
All three are untested for kanna.
- Redosing: no study gave a second dose after a first, so there are no data on stacking amounts within a day. Product pages sometimes set their own daily limits, which reflect each company's caution, not trial results.
- Tolerance breaks: no study tested whether pausing changes later responses.
- Reverse tolerance: the idea that a smaller amount works better over time comes from user reports. We found no study of it for kanna.
If you feel that something is working less well, or you find yourself wanting more than you planned, that is worth discussing with a clinician rather than solving by yourself. If it feels harder to stop than you expected, SAMHSA's National Helpline is free and confidential at 1-800-662-4357 (samhsa.gov).
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
- 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
- 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. PMC
- 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
- National Institute on Drug Abuse. Principles of Drug Addiction Treatment: A Research-Based Guide, 3rd ed. nida.nih.gov
- 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
- Reay J, et al. Sceletium tortuosum (Zembrin) ameliorates experimentally induced anxiety in healthy volunteers. Hum Psychopharmacol 2020;35(6):1-7. 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
- Loria MJ, et al. Effects of Sceletium tortuosum in rats. J Ethnopharmacol 2014;155(1):731-5. PubMed
- 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. PubMed
- Olatunji TL, et al. Sceletium tortuosum: a review on its phytochemistry, pharmacokinetics, biological and clinical activities. J Ethnopharmacol 2021;280:114476. PubMed
- WebMD. Sceletium: Uses, side effects, interactions. webmd.com
- 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
Frequently asked questions
Does kanna build tolerance?
Unknown. We found no clinical study designed to measure tolerance to kanna. Human trials ran from a single dose to 3 months at fixed doses, including one 6-week trial at 25 or 50 mg (Dimpfel 2017) [12], and none reported on tolerance [1][2][3].
Can you take kanna every day?
The longest human trial gave healthy adults 8 mg or 25 mg of one extract once daily for 3 months, and reported good tolerability [1]. That is one extract and 37 people, and it does not establish how any other product behaves. Talk to a clinician, and see kanna dosage.
What is reverse tolerance with kanna?
Reverse tolerance means a smaller amount seems to work better over time. It appears in user reports online, but we found no study of it for kanna. Reports are not evidence.
Do you need a tolerance break from kanna?
There is no research on tolerance breaks for kanna. No study tested whether pauses change anything, so any schedule you read is untested.
Is tolerance the same as tolerability?
No. Tolerance means needing more of something for the same effect. Tolerability means how well people put up with it. The 3-month trial measured tolerability, not tolerance [1].