PNU-96391A (known as OSU6162) is a weak dopamine (DA) D(2) receptor antagonist with behavioral stabilizing properties. OSU6162 seem to act as stabilizers not only on dopaminergic, but also on serotonergic brain signaling (partial agonist on 5-HT2A receptor). OSU6162 in a phase II European clinical trial in treatment of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. One of the isomer of OSU 6162, has promise for treating Parkinson's disease, Huntington's disease and schizophrenia, but both enantiomers of OSU 6162 had dual effects on behavior, stimulating locomotor activity in 'low activity' animals and inhibiting locomotor activity in 'high activity' animals.