Kanna, also known as Sceletium tortuosum, is a plant of the Mesembryathemaceae family.
This plant is native to South Africa with a traditional use in hunter-gatherer populations such as the San and Khoikhoi tribes. Supposedly, these people believed Kanna had great medicinal populations. Kanna was actually most well-known to be chewed on prior to stressful events.
Most of the research behind Kanna uses a product called Zembrin – which are tablets that are claimed to have double the concentration of Kanna’s active components – based on dry weight. Typical doses of Zembrin used in studies (~25mg) equate to ~50mg of Kanna.
Kanna Health Benefits (Science-Backed)
Kanna May Reduce Anxiety
Anxiety is characterized by excess cognitive responses to mild threats.
Zembrin has demonstrated that it acts on the central nervous system, increasing the levels of serotonin (the “happy chemical”) and brain-derived neurotrophic factor .
The supplement achieves this biological effect by inhibiting the reuptake of serotonin into cells after it has been secreted, and by inhibiting the activity of the PDE4 enzyme.
Serotonin is a neurotransmitter in the human body that can regulate mood and social behaviour, with low levels being linked to increased anxiety and depression.
PDE4 is an enzyme which degrades a chemical messenger called cAMP, that would typically increase brain-derived neurotrophic factor . As Zembrin inhibits PDE4, this can increase the levels of cAMP, and therefore benefit one’s mood and reduce anxiety.
Interestingly, combining serotonin reuptake inhibitors with PDE4 inhibitors may have synergistic effects for aiding central nervous system disorders. The mechanisms for this synergistic effect are unknown, but the therapeutic benefit is seen to be larger than taking either drug in isolation .
As Zembrin can achieve both these effects in a single supplement, it can essentially “kill two birds with one stone”. Zembrin, or Kanna, is not currently being used in clinical settings, although other seratonin reuptake inhibitors are widely used for the treatment of anxiety disorders and depression .
When tested in rats, supplementation of 5-20mg/kg of a kanna extract for ~2 weeks noted reduced anxiety and attenuated any increases in corticosterone – a major stress hormone. Interestingly, lower doses of this kanna extract were more effective than the higher doses .
More recently, studies in humans that measure brain activity using MRI scans, Zembrin was shown to dampen the capacity of certain brain regions (amygdala) to react to emotional information .
However, more clinical evidence is needed to confirm the true effects of Kanna and Zembrin.
Currently, doses of 25mg of Zembrin taken prior to an anxiety-induced task have been found to be effective attenuating subcortical threat responsivity and also reducing emotional reactivity in the brain .
Kanna May Help With Depression
Nearly 10% of adults report having frequent signs of depression . Products to combat the origin of the physiological issue, or to reduce the symptoms of depression, are now a major market for the supplement industry.
In rats, administration of Kanna appears to have some degree of antidepressive effect, indicated by a loss of voluntary muscle control during a swim test .
In humans, 25mg of Zembrin has also indicated been noted to improve the Hamilton depression rating scale by ~10% in nondepressed subjects compared to placebo .
Much lower doses of Zembrin, ~10mg, have also led to subjective reports of ‘uplifted spirits’ .
It is thought that Kanna has a close resemblance to the physiological mechanisms of Rolipram -an anti-depressant drug that inhibits PDE4 – that has been very effective in both animal  and clinical studies .
More human trials are needed on Kanna, or Zembrin, especially in depressed patients, in order to provide a more conclusive analysis.
Kanna Safety And Side Effects
Despite some promising evidence for the use of Kanna in pre-clinical trials, supplementation often leads to side effects such as nausea and vomiting .
However, the likelihood of side effects is largely dependent on the dosage used. Reviews state that Zembrin is generally safe and well-tolerated at doses <25 mg when taken orally  – although these reviews mainly assess cardiovascular health as opposed to other reported side-effects.
In terms of any major health concerns, animal studies show that high doses of Kanna failed to show any toxicological signs up to the no observable adverse effect limit of 5,000mg/kg bodyweight, which is approximately 1,800-fold higher than the recommended human intake of 25mg daily . The extent to which this translates to human physiology is yet to be found, but it is can be assumed that Kanna is not toxic at reasonable dosages.
Kanna is a plant that was historically used by African tribes to reduce anxiety and depression.
Nowadays, kanna and its extracts are sold mainly as a dietary supplement in tablet form – usually by the name Zembrin.
There is strong evidence in animal studies that the administration of Zembrin can reduce anxiety and depression, with some recent clinical data in humans also showing this effect.
The safety of Zembrin supplementation is not fully known. It does not seem to have any major side effects at doses under 25mg per day, although nausea and vomiting have been reported.