How Does Kanna Work?
Two lab findings, one counter-finding, and a long list of things nobody has measured in people yet.
How does kanna work? The short version is that lab studies suggest two actions: blocking the serotonin transporter and inhibiting an enzyme called PDE4. The longer version is that these are test-tube and animal findings, the mechanism is still being argued about, and no human trial has confirmed either action in a living person. This post walks through what was found, what it can and cannot tell you, and why it matters for medication safety.
In lab tests, kanna's mesembrine-type alkaloids bound the serotonin transporter, and a standardized extract inhibited the enzyme PDE4 [1]. A cell study argued monoamine release may come first [2]. Kanna is not an SSRI or any approved drug, no human trial measured these actions directly, and the proposed serotonin activity is why medication interactions are a concern.
Which compounds in kanna are active?
The mesembrine-type alkaloids are the main suspects, chiefly mesembrine and mesembrenone. Researchers have identified around 25 alkaloids in the plant, with the mesembrine class predominant, as covered in what is kanna and, in more depth, in our mesembrine guide.
A review of the chemistry describes mesembrine and mesembrenone as the two major active alkaloids and says they are still being characterized [3]. Alkaloid content varies a lot between plants and extracts, which is one reason results from one extract do not carry over to another. In Zembrin, the standardized extract used in most human work, the four main alkaloids made up 0.4% of the extract in the Chiu trial [4], and in one analysis mesembrenone made up about 48% of those alkaloids and mesembrine about 13% [5].
What does kanna do to the serotonin transporter?
In lab binding tests, the extract and several of its alkaloids latch onto it. The serotonin transporter (also called SERT or the 5-HT transporter) is the protein that clears serotonin from the gap between nerve cells.
In a 2011 study, a standardized kanna extract blocked ligand binding at the transporter with an IC50 of 4.3 µg/ml. Of three purified alkaloids tested, mesembrine was the most potent (Ki 1.4 nM), and mesembrenone was active at the transporter as well [1]. IC50 and Ki are measures of how much of a substance it takes to block half of the activity, or how tightly it binds; lower numbers mean stronger action in that assay. These are concentrations in a dish. How much of any alkaloid reaches the brain after a normal oral dose is a separate question that we could not answer from the sources we reviewed.
What is PDE4 and what does kanna do to it?
PDE4 belongs to the phosphodiesterase family, enzymes that break down cyclic nucleotides such as cAMP, messenger molecules that relay signals inside cells [6]. In the same 2011 study the extract had a strong inhibitory effect on PDE4 (IC50 8.5 µg/ml) but not on other phosphodiesterases, and mesembrenone was active against both PDE4 and the serotonin transporter [1].
The study's authors suggested that these two actions may explain the clinical effects of the plant. That was a hypothesis then, and it remains one. A related 2013 brain imaging study titled its result "a dual 5-HT reuptake and PDE4 inhibitor," but the scan measured amygdala activity, not either target [7]. See what the research says about stress and focus for that study.
Is the mechanism settled?
No. At least three findings pull in different directions.
- Release versus reuptake. A 2016 cell study of a high-mesembrine extract (Trimesemine) found it down-regulated the serotonin transporter much as the SSRI citalopram did, and increased a vesicular monoamine transporter. The authors concluded that reuptake inhibition may be secondary to monoamine-releasing activity. The extract also mildly inhibited the enzyme MAO-A in the dish [2]. This was done in cultured human astrocytes and mouse hippocampal cells, not in people.
- Which alkaloid does what. In a 2024 zebrafish larvae study of Zembrin, only mesembrine reproduced the extract's anxiolytic-like behavior, while an antidepressant-like effect in a reserpine model appeared only at higher extract concentrations and with no single alkaloid responsible. The authors suggested several constituents may work together [8].
- Other neurotransmitters. A 2025 mouse study of two wild-collected chemotypes found raised noradrenaline and lowered GABA in brain regions after 35 days of dosing, with the effect differing from a commercial extract [9]. Different plants, different chemistry, different effects.
The common thread: kanna probably touches several systems, and which ones matter in a person is unknown. Rodent and fish behavior tests are screening tools and do not translate directly to people.
Is kanna an SSRI?
No. SSRIs, or selective serotonin reuptake inhibitors, are prescription antidepressants [10]. They are single, purified, dose-controlled drugs with decades of human testing. Kanna is a plant extract with dozens of compounds, varying content and a handful of small trials.
The overlap is real but partial: in the lab some kanna alkaloids act on the same transporter that SSRIs target, and one cell study compared an extract's effect directly with citalopram's [2]. That overlap is the reason caution is warranted, not a sign that kanna works like a medication. Saying it "boosts serotonin" would overstate the evidence, and we avoid the phrase.
What has been shown in people?
Outcomes, not mechanisms. Human trials have measured an amygdala scan, cognitive tests and rating scales, in healthy volunteers [4][7]. None of the trials we found measured serotonin levels, transporter occupancy or PDE4 activity, so the lab mechanism has not been tested in a person. We summarize every published trial in the clinical studies table and the plain-English view in what the research actually shows.
Why does the mechanism matter for safety?
Because serotonin-active substances can add up. The NIMH warns that mixing antidepressants with other drugs or supplements that affect serotonin, such as migraine triptans or St. John's wort, can trigger serotonin syndrome, a rare but life-threatening illness with symptoms including agitation, muscle twitches, hallucinations and high fever [10].
WebMD's page on sceletium lists possible interactions with MAOIs, SSRIs, SNRIs, tricyclic antidepressants, antipsychotics, triptans and St. John's wort, and says the interactions are not fully understood. It also states that it is not known whether sceletium affects pregnancy or passes into breast milk [11]. No one has published a controlled human study of kanna combined with these medicines, so the honest position is that the risk is unquantified. Talk to a doctor or pharmacist before using kanna if you take any of them, and read kanna and drug interactions, kanna and SSRIs and our safety guide.
This page is general information, not medical advice. These statements have not been evaluated by the FDA. Kanna products are not intended to diagnose, prevent or manage any disease or health condition. kannadrinks.com is published by Psilly Goose, a kanna drink maker.
References
- 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. J Ethnopharmacol 2011;137(3):1124-9. PubMed
- Coetzee DD, Lopez V, Smith C. High-mesembrine Sceletium extract (Trimesemine) is a monoamine releasing agent, rather than only a selective serotonin reuptake inhibitor. J Ethnopharmacol 2016;177:111-6. PubMed
- Krstenansky JL. Mesembrine alkaloids: review of their occurrence, chemistry, and pharmacology. J Ethnopharmacol 2017 (review). 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
- Gericke J, Lekhooa M, Steyn SF, Viljoen AM, Harvey BH. An acute dose-ranging evaluation of the antidepressant properties of Sceletium tortuosum (Zembrin) versus escitalopram in the Flinders Sensitive Line rat. J Ethnopharmacol 2022 (rat study; cited here for the extract's alkaloid profile only). PubMed
- Cyclic nucleotide phosphodiesterases as drug targets. Pharmacol Rev 2025 (review). 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 Central
- Gericke J, Harvey BH, Pretorius L, Ollewagen T, Benecke RM, Smith C. Sceletium tortuosum-derived mesembrine significantly contributes to the anxiolytic effect of Zembrin, but its anti-depressant effect may require synergy of multiple plant constituents. J Ethnopharmacol 2024. PubMed
- Kaschula CH, et al. Differential impact of extracts from distinct Sceletium tortuosum chemotypes on central neurotransmitter concentrations in C57BL/6 mice. J Ethnopharmacol 2025. PubMed
- National Institute of Mental Health. Mental health medications. nimh.nih.gov
- WebMD. Sceletium: uses, side effects, interactions. webmd.com
Frequently asked questions
How does kanna work in the brain?
In lab tests, kanna alkaloids such as mesembrine bind the serotonin transporter, and a standardized extract inhibited an enzyme called PDE4 [1]. Whether these actions explain anything in people is not established, and one cell study argued the picture is more complicated [2].
Is kanna an SSRI?
No. SSRIs are prescription antidepressants with a defined, tested action. Kanna is a plant extract whose alkaloids showed some overlapping activity at the serotonin transporter in the lab. That overlap is why combining it with serotonergic medicines is a concern.
Does kanna boost serotonin?
That is an oversimplification we avoid. Lab work shows binding to the serotonin transporter and, in one study, signs of monoamine release [1][2]. No human trial we found measured serotonin levels or transporter occupancy.
What is PDE4 and why does it matter for kanna?
PDE4 is an enzyme that breaks down cAMP, a signaling molecule inside cells. A standardized kanna extract inhibited PDE4 in a lab assay [1]. What that does in the body after a normal dose is not known.
Is it safe to take kanna with antidepressants?
Not without medical advice. Because kanna's alkaloids act on the serotonin transporter in lab tests, combining it with SSRIs, SNRIs, MAOIs, triptans or St. John's wort is a recognized concern. See kanna and SSRIs.