Flupirtine, a chemically unique, orally effective, non-narcotic, centrally acting analgesic was evaluated for efficacy and safety in five parallel, double-blind randomized clinical trials which included both placebo and active control comparisons. Flupirtine was given in oral doses of 100 to 300 mg, with a maximum daily dose of 600 mg to patients with pain resulting from episiotomy, surgical or dental procedures. Patients rated pain intensity, pain relief and adverse experiences at regular intervals up to 6 hours following medication. Assessments of efficacy included measures of the sum of pain intensity differences (SPID), total pain relief (TOPAR) and peak analgesia (PPID). More than 1300 patients have been evaluated at 26 study sites in the United States. More than 170 of them received flupirtine 100 mg, 250 received 200 mg and 50 received 300 mg. An additional 415 patients received positive control medications (paracetamol 650 mg, codeine 60 mg, pentazocine 50 mg or oxycodone 10 mg plus paracetamol 650 mg). All doses of flupirtine produced analgesia after a single dose. Pharmacokinetic evaluations have shown linear kinetics for flupirtine and a 100 mg t.i.d. dosage schedule produces average steady-state blood levels equivalent to the peak response for a single 200 mg dose. Adverse experiences occurring in flupirtine clinical studies have been minimal in incidence, nature and degree, with drowsiness being the most frequently reported reaction (approximately 10%).