Tetrahydroberberine is an isoquinoline alkaloid isolated from corydalis tuber; has micromolar affinity for dopamine D(2) (pK(i) = 6.08) and 5-HT(1A) (pK(i) = 5.38) receptors but moderate to no affinity for other relevant serotonin receptors (5-HT(1B), 5-HT(1D), 5-HT(3), and 5-HT(4); pK(i) < 5.00).