Background: Rapid I-131 turnover Graves’ disease patients have low cure rate. We aimed to compare cure percentage at 12 months among 3 treatment doses of I-131 with or without lithium carbonate (LiCO 3 ) in rapid turnover Graves’ disease patients. Methods: Sixty Graves’ disease patients referred for radioactive iodine treatment were randomised into three arms of treatment: Group A, 3.7 MBq I-131/g thyroid plus 600 mg/day LiCO 3 , Group B, 5.55 MBq I-131/g plus 600 mg/day LiCO 3 , and Group C, 7.4 MBq I-131/g without LiCO 3 . Data were collected at baseline, 3, 6, 9, and 12 months. The primary endpoint were cure rates (percentage of euthyroid or hypothyroid) at 12 months. Pairwise comparisons were made across 3 groups using an equality of proportions test. The secondary endpoint, the odds of cure over the total follow-up for group B and C versus group A, was analyzed using generalized estimating equation (GEE). Side effects of I-131 and LiCO 3 treatment were evaluated at 1 to 2 weeks after treatment. Results: The cure rate at 12 months was 45% (9/20) for group A, 60% (12/20) for group B and 80% (16/20) for group C. The mean difference in proportion cured at 12 months between group C and group A was 35 (7.0 to 66.8)%; P -value = .02. There was a statistically significant difference between cure rates over all follow-up of group C and A after adjustment for sex (adjusted OR = 3.09; 95%CI = 1.32–7.20; P -value = .009), but no significant difference was found between group B and A or C and B in the primary and/or secondary efficacy endpoints. Side effects from the treatment were found in 12% (7/60); 2 in group A, 4 in group B, and 1 in group C. Four of these were likely due to LiCO 3 side effects. Conclusions: Treatment of rapid turnover Graves’ disease patients with high dose I-131 (7.4 MBq/g) provides significantly higher cure rates at 12 months, and 3 times odds of cure than 3.7 MBq/g I-131 plus LiCO 3 with lesser side effects. We thus recommend 7.4 MBq I-131/g for treatment in these patients.