Abstract:Background: Many health benefits of bariatric surgery are known and well-studied, but there is scarce data on the benefits of bariatric surgery on the thyroid function. Objective: We aimed to make a meta-analysis regarding the impact of bariatric surgery on thyroid-stimulating hormone (TSH) levels, levothyroxine dose, and the status of subclinical hypothyroidism. Setting: Systematic review and meta-analysis. Methods: PubMed, EMBASE, and Cochrane Library were searched up to December 2020 for relevant clinical studies. Random-effects model was used to pool results. Network meta-analysis was performed, incorporating direct and indirect comparisons among different types of bariatric surgery. Meta-regression analysis was performed to evaluate the impact of moderator variables on TSH levels and required levothyroxine dose after surgery. We followed the PRISMA guidelines for data selection and extraction. PROSPERO registry number: CRD42018105739. Results: A total of 28 studies involving 1284 patients were included. There was a statistically significant decrease in TSH levels after bariatric surgery (mean difference = −1.66 mU/L, 95%CI [−2.29, −1.03], P <.0001). In meta-regression analysis, we found that the following moderator variables: length of follow-up, mean age, baseline TSH, and preoperative thyroid function, could explain 1%, 43%, 68%, and 88% of the between-study variance, respectively. Furthermore, subclinical hypothyroidism was completely resolved in 87% of patients following bariatric surgery. In addition, there was a statistically significant decrease of levothyroxine dose in frank hypothyroid patients following bariatric surgery (mean difference = −13.20 mcg/d, 95%CI [−19.69, −6.71]). In network meta-analysis, we found that discontinuing or decreasing levothyroxine dose was significant following Roux-en-Y gastric bypass, 1 anastomosis gastric bypass, and sleeve gastrectomy, (OR = 31.02, 95%CI [10.34, 93.08]), (OR = 41.73, 95%CI [2.04, 854.69]), (OR = 104.03, 95%CI [35.79, 302.38]), respectively. Conclusions: Based on our meta-analysis, bariatric surgery is associated with the resolution of subclinical hypothyroidism, a decrease in TSH levels, and a decrease in levothyroxine dose.