Sceletium tortuosum is a plant indigenous to South Africa with a long history of use for enhancing mood, memory, physical endurance, and other functions; however, historical use alone does not equal efficacy. Compounds present in Sceletium tortuosum have several biological targets, including serotonin, which can affect mood and cognitive functions. A few, small, short-duration clinical trials have suggested that Sceletium tortuosum extracts may improve some complex cognitive functions; however, evidence from large, long-term studies is lacking. Sceletium tortuosum extracts are generally well-tolerated, but long-term safety has not been established.
Only a few small, short-term clinical trials have tested the effects of Sceletium tortuosum on cognitive function, with mixed findings. Our search identified:
Sceletium tortuosum has a long history of use in South Africa for improving mood, well-being, physical endurance, and some cognitive functions; however, validation based on modern clinical testing is limited. No clinical trials have tested whether Sceletium tortuosum (also known as Mesembryanthemum tortuosum and commonly referred to as “kanna” or “kougoed”) can prevent dementia or age-related cognitive decline [1]. Only two studies have tested the effects of Sceletium tortuosum on cognitive functions, one in young adults and the other in middle-aged adults; no studies have tested Sceletium tortuosum in older adults with cognitive symptoms.
In a randomized placebo-controlled trial of 21 cognitively healthy middle-aged people (45-65 years old), treatment with Zembrin, a standardized extract of Sceletium tortuosum (25 mg, once daily, orally), for three weeks improved complex cognitive functions, including cognitive flexibility and executive function, compared with placebo [2]. Participants taking the Sceletium tortuosum extract also reported improvement in their subjective quality of sleep and sleep onset compared to placebo. However, Sceletium tortuosum treatment did not affect other cognitive functions, including verbal memory, visual memory, processing speed, psychomotor speed, reaction, or complex attention.
In a randomized placebo-controlled trial of 60 physically active men and women aged 20-35, Sceletium tortuosum extract (Zembrin) treatment (25 mg, once daily, orally) for eight days significantly improved complex reactive performance (requiring responses to repeated visual stimuli with a cognitive load) compared with placebo [3]. The extract was also associated with a significantly higher reactive agility compared to placebo in a task that required decision making. However, no significant differences between Sceletium tortuosum extract and placebo groups were observed for visual tracking performance, motor reaction time, visual reaction time, physical reaction time, anxiety, depression, anger/hostility, vigor, confusion, subjective feelings of alertness, or subjective energy.
Based on the limited available evidence from clinical trials, it is possible that Sceletium tortuosum may improve cognitive functions with high complexity or stress/load without affecting simpler cognitive tasks. However, larger, longer-duration, rigorously-designed clinical trials are needed to validate these preliminary findings.
No clinical trials have tested the efficacy of Sceletium tortuosum in people with dementia.
Sceletium tortuosum has a long history of use in South Africa, but long-term safety beyond three months has not been established in clinical trials. Based on a double-blind randomized placebo-controlled trial in healthy adults, the standardized Sceletium tortuosum extract, Zembrin (8 or 25 mg, once daily, orally), for three months was well tolerated, with the placebo group experiencing a higher incidence of adverse events [4]. No significant effects of the Sceletium tortuosum extract were seen on vital signs, electrocardiograms, body weight, physical examination, or hematology and biochemistry parameters. The most commonly reported adverse event in the trial was headache, which had a higher incidence with placebo than with the extract. In a randomized placebo-controlled trial of cognitively healthy middle-aged people (45-65 years old), Sceletium tortuosum treatment (Zembrin; 25 mg capsule once daily) for three weeks resulted in less frequent adverse events than placebo [2]. There were no changes in blood pressure, pulse, temperature, or weight with the extract. Some subjects taking the extract reported transient gastrointestinal discomfort.
There are no reports to date of herb-drug interactions with Sceletium tortuosum [1]. However, based on its mechanisms of action, it should not be used with drugs known to alter serotonin uptake or release, including the antidepressants, SSRIs and SNRIs. Another drug that may interact with Sceletium tortuosum based on its inhibitory action towards phosphodiesterase 4 (an enzyme that helps to regulate inflammation), is roflumilast (approved in the US and EU for treating severe chronic obstructive pulmonary disease).
NOTE: This is not a comprehensive safety evaluation or complete list of potentially harmful drug interactions. It is important to discuss safety issues with your physician before taking any new supplement or medication.
Sceletium tortuosum supplements are available in the forms of tablets, capsules, and tincture. The total bioactive alkaloid content of Sceletium tortuosum is variable. Zembrin is a standardized water and ethanol extract of Sceletium tortuosum that contains a total alkaloid content (mesembrenone, mesembrenol, mesembranol, and mesembrine) of around 0.4%. The most commonly tested Zembrin dose is 25 mg, daily, orally [2; 3; 4], which is equivalent to 50 mg of dry raw Sceletium tortuosum.
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