Synephrine Hcl(Oxedrine) is an alkaloid; synephrine produces most of its biological effects by acting as an agonist at adrenergic receptors. IC50 value: Target: adrenergic receptor agonist There is some evidence that synephrine also has weak activity at 5-HT receptors, and that it interacts with TAAR1 (trace adrenergic amine receptors). d-synephrine inhibited the uptake of [3H]-norepinephrine with an IC50 = 5.8 μM; l-synephrine was less potent (IC50 = 13.5 μM). d-Synephrine also competitively inhibited the binding of nisoxetine[m] to rat brain cortical slices, with a Ki = 4.5 μM; l-synephrine was less potent (Ki = 8.2 μM). In experiments on the release of [3H]-norepinephrine from rat brain cortical slices, however, the l-isomer of synephrine was a more potent enhancer of the release (EC50 = 8.2 μM) than the d-isomer (EC50 = 12.3 μM). This enhanced release by l-synephrine was blocked by nisoxetine.