Compounds of formula (a), (b), (c), or (d), or any mixture thereof, or a pharmaceutically-acceptable salt thereof; wherein R is hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl or 2-hydroxyethyl; R3 is —CH2—X—R′, wherein X is O, S or NR″, wherein R″ is hydrogen or alkyl and R′ is alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl, or —CO-alkyl; R4 is phenyl optionally substituted with halogen, CF3, CN, alkoxy, cycloalkoxy, alkyl, cycloalkyl, alkenyl, alkynyl, amino, nitro, heteroaryl, or aryl; 3,4-methylenedioxyphenyl; benzyl optionally substituted with halogen, CF3, CH, alkoxy, cycloalkoxy, alkyl, cycloalkyl, alkenyl, alkynyl, amino, nitro, heteroaryl, or aryl; heteroaryl optionally substituted with halogen, CF3, CN, alkoxy, cycloalkoxy, alkyl, cycloalkyl, alkenyl, alkynyl, amino, nitro, heteroaryl, or aryl; or naphthyl optionally substituted with halogen, CF3, CN, alkoxy, cycloalkoxy, alkyl, cycloalkyl, alkenyl, alkynyl, amino, nitro, heteroaryl, or aryl. The compounds are monoamine neurotransmitter, i.e., dopamine, serotonin, noradrenaline, reuptake inhibitors.