- Changes in serum creatine phosphokinase have been associated with exacerbation of tardive dyskinesia. Vitamin E, a drug suggested to be effective in the treatment of tardive dyskinesia, has been implicated as a possible cause of increased creatine phosphokinase levels. Ten patients with long-term tardive dyskinesia were treated with vitamin E in a double-blind, placebo-controlled crossover study. Vitamin E blood levels and creatine phosphokinase serum levels were monitored at various phases during the study. There were no significant differences between vitamin E and placebo treated patients in their abilities to affect tardive dyskinesia or to influence creatine phosphokinase levels. These data do not support the hypothesis that administration of vitamin E may alter creatine phosphokinase levels in patients with long-term tardive dyskinesia.