Paynantheine (Item No. 21841) is an alkaloid of the herbal drug M. speciosa (also known as kratom). Kratom (mitragynine; Item Nos. 11151 | 18567) has opioid-like and stimulant effects, and paynantheine can be detected in urine after kratom ingestion. Paynantheine blocks the delayed-rectifier potassium current in human induced pluripotent stem cell-derived cardiomyocytes (IC50 = 2.47 μM), suggesting that it may have cardiotoxic effects. This product is intended for research and forensic applications.