Mesembrine is an alkaloid present in Sceletium tortuosum (kanna). It has been shown to act as a serotonin reuptake inhibitor (K = 1.4 nM), and more recently, has also been found to behave as a weak inhibitor of the enzyme phosphodiesterase 4 (PDE4) (K = 7,800 nM). In an in vitro study published in 2015, researchers concluded that "a high-mesembrine Sceletium extract" may exert anti-depressant effects by acting as a monoamine releasing agent." As such, mesembrine likely plays a dominant role in the antidepressant effects of kanna. The levorotatory isomer, (−)-mesembrine, is the natural form.
Rat studies have evaluated effects of kanna extract, finding analgesic and antidepressant potential.  No adverse results were noted for a commercial extract up to 5000 mg/kg daily in rats.
Mesembrine has also been identified in Mesembryanthemum cordifolium, Delosperma echinatum and Oscularia deltoides.