Caffeine and guarana:
Consumers should be aware that guarana has one of the highest concentrations of caffeine in any plant and intake of this herb supplement is not advised. The amount of caffeine in guarana may not be known, consistent or reliable in supplements. Authors report a case in which an individual taking two herbal supplements suffered from premature ventricular contractions (PVCs) believed to be an adverse effect of the supplements. Both supplements included a variety of herbs but both contained high doses of guarana. Guarana has one of the highest concentrations of caffeine in any plant and is found in many supplements sold in the US. (27)