Data from three placebo-controlled and 11 active-controlled studies of tizanidine were combined to permit analysis of the subsets, which were too small to evaluate within the individual studies. Overall analysis of placebo-controlled data confirms the effectiveness of tizanidine in reducing muscle tone in patients with spasticity of spinal cord origin. Subset analyses suggest that patients with more severe spasticity are more likely to respond, but age, sex, and race were not predictive of response. Comparisons of tizanidine with active controls showed no differences in efficacy compared with baclofen or diazepam. However, when compared with controls, patients treated with tizanidine did not experience increased weakness. Furthermore, patients tolerated tizanidine better than the control medications. More patients experienced adverse events during tizanidine treatment than did patients receiving placebo. The most common adverse events reported were dry mouth, somnolence, asthenia, and dizziness. Mild elevations in liver function tests were noted occasionally, but improved in all patients with dose reduction or withdrawal. Three patients from the double-blind database reported formed visual hallucinations. All three cleared; two continued tizanidine, and one discontinued.