Effects of p -synephrine in combination with caffeine: a review

This review summarizes the current research involving p-synephrine in combination with caffeine. Over 30 clinical human studies with in excess of 700 subjects, and animal and in vitro studies have assessed the safety, efficacy, and mechanism of action of Citrus aurantium (bitter orange) extract and its primary active constituent p-synephrine. Approximately 35% of these human subjects concurrently consumed caffeine, a stimulant thermogenic agent. In these clinical investigations, no serious adverse effects were reported or observed when using the combination of p-synephrine with caffeine. Animal studies with exceedingly high doses of p-synephrine in combination with caffeine support and affirm the human studies. The results of studies conducted to date indicate that p-synephrine does not augment the cardiovascular effects of caffeine or produce cardiovascular effects at commonly used doses. These observations can be explained on the basis of in vitro mechanistic studies. Keywords: caffeine, p-synephrine, bitter orange extract, Citrus aurantium, mechanisms, cardiovascular effects