Yohimbine. Molecular model of the drug yohimbine (C21.H26.N2.O3). This is an indole alkaloid derived from the bark of the Pausinystalia yohimbe tree in Central Africa. Depending on dosage, yohimbine can either increase or decrease systemic blood pressure. Yohimbine has been studied as a potential treatment for erectile dysfunction. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white), nitrogen (blue) and oxygen (red). Illustration.