Kanna Side Effects: What the Studies Recorded
Small trials in healthy adults recorded few adverse events, but the data are short, narrow and mostly tied to one extract.
Kanna side effects are a high-intent search, and the answers online conflict. Some pages say there are none. Others list a dozen. This post sticks to what human studies actually recorded, with the dose, the number of people and how long they were followed, and then says plainly what nobody has measured. It is a spoke of our broader guide, is kanna safe?
WebMD lists headache and upset stomach as the common side effects of sceletium (kanna) [3]. In a 3-month trial of 37 healthy adults taking 8 mg or 25 mg of one extract daily, headache was the most common adverse event and was more frequent on placebo [1]. Long-term effects and effects in people on medication are largely unstudied.
What are the common side effects of kanna?
WebMD names two: headache and upset stomach. It adds that side effects may differ with the dose or the product [3].
It also tells readers to stop using sceletium and get help right away for signs of a serious allergic reaction, which it describes as breathing problems, swelling of the face or throat, hives or fainting [3]. People who are allergic to sceletium or any ingredient in a product should not use it [3].
That short list is consistent with what the trials below saw. It is also a reminder of how thin the evidence is. WebMD is a consumer reference, not a systematic safety database, and the studies behind it were small.
What did the human trials record?
Two controlled trials reported tolerability data; two more report none in their abstracts. All four used the same branded extract, Zembrin, at 25 mg or less per day, though a separate 6-week trial also tested 50 mg (Dimpfel 2017 [12]; see kanna dosage).
| Study | Who, how many | Dose and length | What was recorded |
|---|---|---|---|
| Nell 2013 [1] | 37 healthy adults; 12 on 8 mg, 12 on 25 mg, 13 on placebo | 8 mg or 25 mg once daily for 3 months | No apparent differences in vital signs, ECG, body weight or physical exam; no significant changes in blood counts or chemistry. Most common adverse event was headache, then abdominal pain and upper respiratory infections, all more frequent in the placebo group. |
| Chiu 2014 [2] | 21 healthy adults, mean age 54.6 | 25 mg daily for 3 weeks versus placebo (crossover) | Described as well tolerated. 9.5% of the kanna group reported transient stomach discomfort that resolved on its own. The placebo group reported more adverse events overall. Blood pressure, pulse, temperature and weight did not change significantly. Two participants dropped out during the placebo phase and three during the kanna phase; reasons were not given. |
| Reay 2020 [5] | 20 young healthy volunteers across two experiments | Single 25 mg dose | The abstract reports effects on anxiety and heart rate during lab stress tasks. It does not report adverse events. |
| Hoffman 2020 [6] | 60 recreationally trained adults aged 20 to 35 | 25 mg for 8 days | The abstract reports performance and mood outcomes. It does not report adverse events. |
A 2013 imaging study of 16 healthy participants who received a single 25 mg dose also exists [7]; its abstract does not describe side effects.
Two details are worth underlining. First, in the 3-month trial the common complaints were more frequent on placebo than on kanna. That does not mean kanna prevents headaches. It means that in a small group, ordinary background complaints showed up whatever people took [1]. Second, the Chiu authors wrote that the rate of mild and moderate adverse events was low and that no life-threatening events were found, but they also listed a single dose level, a short period and a small sample as limitations [2].
The Chiu study, for example, excluded pregnancy, active suicide risk, a body mass index above 30 and several serious untreated medical conditions [2]. The people studied were not a cross-section of everyone who might buy a kanna drink.
Are there long-term side effects?
Nobody knows. The longest controlled human safety trial we found ran 3 months [1], and we found nothing that followed people for years.
There is animal data. A 2014 toxicology paper tested the same extract in rats: a 14-day study at up to 5,000 mg/kg per day and a 90-day study at up to 600 mg/kg per day. It reported no mortality or treatment-related adverse effects, and set those top doses as the no-observed-adverse-effect levels [4]. Two cautions apply. Rat results do not carry over directly to people, and the study was run with authors from the company that makes the extract [4].
A 2026 critical review of animal and clinical studies described a "favourable safety profile" but also small samples and studies in clinically irrelevant populations [10]. We read the abstract only, not the full text.
If you want to see what doses those studies used, see kanna dosage. This site does not recommend a dose.
Is kanna hard on the liver?
We found no evidence that it is, and also not much evidence either way. That is a different statement from "it is safe for the liver."
- In the 3-month trial, blood chemistry and blood counts showed no significant changes between the start and end of the study [1].
- We searched PubMed for Sceletium and kanna papers mentioning case reports, toxicity, or adverse events and found no report of liver injury attributed to kanna. We also found no Sceletium entry in NIH's LiverTox database (checked October 29, 2026). Absence of reports is not proof of absence, particularly for a product with few users on record.
- WebMD lists "kidney or liver problems" among the conditions to tell a provider about before using sceletium [3].
- Some kanna drinks also contain kava. The liver questions that apply to kava are a separate issue from kanna; see kanna vs kava.
WebMD also notes that some sceletium products have been found to contain other ingredients, such as ephedrine, which can cause serious side effects [3]. When a reaction happens with a supplement, the product itself is part of the question.
Can kanna cause anxiety or other mood effects?
We did not find a trial that reported anxiety as an adverse effect of kanna, but the trials were not designed to look for it.
Because kanna's lab activity involves the serotonin transporter [11], it is reasonable to ask whether mood-related effects could go either way for some people. That is a hypothesis, not a finding. Individual experiences are not captured by 20-to-60-person studies in healthy volunteers. If a product makes you feel worse, jittery or unwell, stop and talk to a clinician. If you take antidepressants or other serotonin-affecting medicine, see our post on kanna and SSRIs before anything else.
When is a side effect serious?
Allergic signs (trouble breathing, swelling of the face or throat, hives, fainting) call for stopping and getting help right away [3]. Symptoms that suggest too much serotonin call for contacting a provider right away.
MedlinePlus describes serotonin syndrome as a reaction usually seen when two or more serotonin-affecting medicines or substances are combined. Symptoms can begin within minutes to hours and include agitation or restlessness, fast heartbeat, high blood pressure, diarrhea, overactive reflexes, loss of coordination, nausea and a rise in body temperature [8]. No case of serotonin syndrome attributed to kanna turned up in our PubMed search, and the interaction question is covered in kanna drug interactions. If you are not sure whether something is an emergency, WebMD lists Poison Control at 800-222-1222 for overdose concerns [3].
Kanna may also matter in specific situations such as pregnancy, surgery or other medicines. Those are in who should not take kanna.
Why do the numbers not tell the whole story?
Because the evidence has four built-in limits, and a clean-looking table can hide them.
- Small and short. Thirty-seven people for 3 months is the longest, and three weeks or less is more typical [1][2][5][6].
- Healthy volunteers. A 2021 review notes the plant has not yet been studied in a clinical population [9].
- One extract. Zembrin is a standardized extract. Other products differ in alkaloid content, and WebMD notes that chemistry can vary with growing conditions, harvest timing and processing, so effects may differ between brands [3].
- Industry links. Several of these papers have authors tied to the company that owns Zembrin [2][4].
Kanna drinks add a fifth issue: labels range widely in milligrams and extract type, so a published trial dose does not map neatly to a can. Our ranking of kanna drinks lists what each label states.
This page is general information, not medical advice, and it cannot tell you whether kanna is right for you. Talk to a doctor or pharmacist, especially if you take any medicine. Do not stop or change a prescribed medicine on your own. These statements have not been evaluated by the FDA, and kanna products are not intended for any disease or health condition.
References
- 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. 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. PubMed Central
- WebMD. Sceletium: Uses, side effects, interactions. webmd.com
- Murbach TS, Hirka G, Szakonyine IP, Gericke N, Endres JR. A toxicological safety assessment of a standardized extract of Sceletium tortuosum (Zembrin) in rats. Food Chem Toxicol 2014;74:190-9. PubMed
- Reay J, Wetherell MA, Morton E, Lillis J, Badmaev V. Sceletium tortuosum (Zembrin) ameliorates experimentally induced anxiety in healthy volunteers. Hum Psychopharmacol 2020;35(6):1-7. PubMed
- 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. J Strength Cond Res 2020;34(9):2476-81. 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. PubMed
- MedlinePlus. Serotonin syndrome. National Library of Medicine. medlineplus.gov
- Olatunji TL, et al. Sceletium tortuosum: a review on its phytochemistry, pharmacokinetics, biological and clinical activities. J Ethnopharmacol 2021;280:114476. 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
- 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
- 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
What are the side effects of kanna?
WebMD lists headache and upset stomach as the common ones, and says effects may vary with dose or product [3]. In a 3-month trial of 37 healthy adults, headache was the most commonly reported adverse event, and it occurred more often in the placebo group [1].
Does kanna cause headaches or an upset stomach?
It can be listed that way: WebMD names both [3]. In the trials we read, the numbers were small. In a 3-week crossover study of 21 adults, 9.5% on kanna reported transient stomach discomfort that resolved on its own [2]. In the 3-month study, headaches were more common on placebo [1].
Are there long-term side effects of kanna?
Unknown. The longest controlled human safety trial we found lasted 3 months [1]. Rats given the same extract for 90 days showed no treatment-related adverse effects [4], but rat data do not settle the question for people.
Is kanna hard on the liver?
We found no case report of liver injury attributed to kanna and no kanna entry in NIH's LiverTox database (checked October 29, 2026). In the 3-month trial, blood chemistry showed no significant changes [1]. That is reassuring but limited to 37 healthy adults. Tell your clinician if you have liver or kidney problems [3].
When should I stop and get help?
WebMD says to stop sceletium and get help right away for signs of a serious allergic reaction such as breathing problems, swelling of the face or throat, hives or fainting [3]. If you take serotonin-affecting medicine and develop agitation, fast heartbeat or fever, contact a provider right away [8].