Kanna (Sceletium tortuosum) appears to be safe at low, standardized doses based on the limited clinical evidence available. In a three-month human trial, daily doses of 8 mg and 25 mg of a standardized extract produced no concerning changes in blood pressure, heart rate, ECG readings, or body weight compared to placebo. That said, kanna is a psychoactive plant that affects serotonin activity in the brain, and the safety picture gets more complicated at higher doses, with unstandardized products, or if you take certain medications.
How Kanna Works in the Brain
Kanna contains a group of alkaloids, the most important being mesembrine and mesembrenone. These compounds do two things. First, they block the serotonin transporter, the same molecular target that prescription antidepressants like SSRIs act on. Mesembrine is especially potent here. Second, mesembrenone inhibits an enzyme called PDE4, which plays a role in inflammation and mood regulation. This dual action on serotonin and PDE4 is what gives kanna its reputation for reducing anxiety and lifting mood.
There is also evidence that kanna compounds can inhibit a brain enzyme involved in breaking down certain neurotransmitters (MAO-B), and may interact with receptors involved in learning and memory. These are relatively mild effects at typical doses, but they matter when you start combining kanna with other substances that affect the same systems.
What Clinical Trials Found
The most rigorous safety data comes from a randomized, double-blind, placebo-controlled trial using a standardized extract called Zembrin. Healthy adults took either 8 mg or 25 mg daily for three months. Both doses were well tolerated. The most common side effect reported across the entire study was headache, but it actually occurred more often in the placebo group than in the groups taking kanna. The same was true for abdominal pain and upper respiratory infections.
A smaller proof-of-concept study did flag some side effects that occurred more in the kanna group than in placebo: weight gain (14% of participants), increased appetite (10%), increased thirst (10%), and tiredness (10%). Less common effects, each reported by about 5% of participants, included nausea, constipation, drowsiness, difficulty concentrating, chest pain, and confusion. These numbers come from a small sample, so they should be taken as signals rather than precise risk estimates.
Animal toxicity studies offer additional reassurance at reasonable doses. In a 90-day study, rats given kanna extract daily showed no mortality or treatment-related adverse effects even at the highest dose tested, which was far above what any human would take.
Dose Matters More Than You Think
One of the biggest safety variables with kanna is how much active alkaloid you’re actually consuming, and this varies enormously across products. Clinical trials used 25 to 50 mg of Zembrin daily, a standardized extract containing just 0.4% total alkaloids. That translates to roughly 100 to 400 micrograms of alkaloids per day, a very small amount.
Traditional use in South Africa involved chewing 500 to 1,500 mg of raw plant material, which could deliver anywhere from 0.25 to 34.5 mg of total alkaloids depending on the plant’s potency. Dietary supplements sold online deliver between 50 and 680 mg of dried plant material or extract per serving, with alkaloid content ranging from 1 to 13.6 mg. That means some supplements deliver roughly 30 to 60 times more active alkaloid than what was tested in clinical trials. The safety profile established in studies does not automatically apply to high-dose products.
If you’re choosing a kanna product, the total alkaloid content per serving is a more meaningful number than the milligrams of raw material. Products that list a standardized alkaloid percentage give you much more predictable dosing than those selling crude plant powder.
Drug Interactions and Serotonin Risk
The most important safety concern with kanna is its interaction with medications that affect serotonin. Because kanna blocks the serotonin transporter through the same mechanism as SSRIs and SNRIs, combining them could theoretically push serotonin levels dangerously high, a condition called serotonin syndrome. Symptoms range from agitation, rapid heartbeat, and diarrhea to muscle rigidity, seizures, and in rare cases, life-threatening complications.
No formal herb-drug interaction studies have been published, and no case reports of serotonin syndrome from kanna have been documented as of the available literature. But the absence of reports is not the same as proof of safety, especially given that kanna’s use outside of southern Africa is relatively recent. The Alzheimer’s Drug Discovery Foundation notes that based on its mechanism of action, kanna should not be used with drugs that alter serotonin uptake or release, including SSRIs and SNRIs.
Kanna may also interact with drugs that inhibit PDE4, such as roflumilast (used for severe COPD). If you take any psychiatric medication, combining it with kanna introduces unpredictable risk.
Product Quality Is Unregulated
Kanna is sold as a dietary supplement in most markets, which means it doesn’t go through the same testing and approval process as pharmaceutical drugs. Alkaloid content can vary widely between brands and even between batches from the same brand. Some products use raw dried plant material, others use extracts standardized to a specific alkaloid percentage, and some don’t disclose alkaloid content at all.
This inconsistency is a practical safety issue. Two products that both say “500 mg kanna” on the label could deliver dramatically different amounts of active compound. Standardized extracts with third-party testing provide the closest thing to a reliable dose. Products that list only raw plant weight, without alkaloid standardization, leave you guessing about what you’re actually taking.
Pregnancy, Breastfeeding, and Other Gaps
There is no published safety data on kanna use during pregnancy or breastfeeding. Clinical trials have only been conducted in healthy adults without serious medical conditions. Given that kanna actively modifies serotonin signaling, a system that plays important roles in fetal brain development, the lack of data here is a meaningful gap rather than a minor footnote. The same applies to children and adolescents, for whom no studies exist.
Long-term human safety data beyond three months is also missing. The three-month trial showed no accumulating problems, but that’s a relatively short window for a supplement some people take indefinitely. Animal studies out to 90 days were clean, but animal models don’t always predict human outcomes, particularly for neurological effects.