GABA (γ-amino butyric acid) is the major inhibitory transmitter in the central nervous system. THIP (4,5,6,7-tetrahydroisozazole(5,4c) pyridine-3–01) is a structurally rigid GABA-mimetic drug. In a single-blind trial, THIP, administered in a single oral dose to patients suffering from chronic, nonmalignant pain, was found to exert a definite analgesic effect compared with placebo (p < 0.05). The analgesic effect did not improve following a 2.5− fold increase in dose, and the side effects (dizziness, sedation, and nausea) were dose dependent and more frequent at high serum concentrations. There was no correlation between THIP serum concentration and analgesic effect. The study shows that THIP in a dose of about 0.1 mdkg body weight might be used in the treatment of chronic pain, but the therapeutic range is very narrow.