( c ) drugs enhancing serotoninergic neurotransmission ( e.g . the serotoninergic precursors tryptophan and 5-hydroxytryptophan , direct-acting serotonin agonists such as quipazine and mk 212 , and indirect-acting serotonin agonists such as fenfluramine ) ;
C0041249
tryptophan
C0000578
5-hydroxytryptophan