Purpose To evaluate the effectiveness of super blue-green algae (SBGA) supplements on the severity of essential blepharospasm treated with botulinum toxin A injections. Design Double-masked, placebo-controlled, two-period, crossover randomized trial. Patients and methods The study was carried out in patients with essential blepharospasm or Meige syndrome undergoing routine treatment with botulinum toxin A injections. Intervention Patients were randomly assigned to either SBGA capsules or placebo. After 6 months of treatment, patients underwent a 6-month washout period with no treatment, then were administered the alternate treatment for an additional 6 months, thus serving as their own controls. Main outcome measures Video documentation of blink rate and involuntary facial movements, time between botulinum toxin A injections, and patients' subjective assessment of the impact of blepharospasm on functioning were obtained at the beginning and end of the first and second (crossover) treatment periods. Results A total of 24 patients (10 men, 14 women; aged 42 to 83 years) completed both treatment periods. Mean within-patient difference in blink rate between SBGA and placebo periods was -2.1 blinks per 2 minutes (95% confidence interval [CI]: -20.8-+31.9), not statistically different from zero (P = .83). Mean within-patient difference in time between injections between SBGA and placebo periods was 4.6 days (95% CI: -13.3-+22.5), not statistically different from zero (P = .62). The lack of statistical significance may have been because of small sample size. There were no significant differences in severity of involuntary movement between SBGA and placebo treatment periods. However, patients were more likely to report limitation in function during the period they took SBGA than during the period they took placebo (odds ratio, 0.2; P = .03). Conclusion Overall, we found no evidence of a beneficial effect of SBGA as an adjunct to botulinum toxin A injections; however, a few patients, all younger than 60 years, did appear to benefit from SBGA. © 2004 by Elsevier Inc. All rights reserved.