Items		(1) Health‐related quality of life	(2) Hypothyroidism	(3) Adverse events	(4) All‐cause mortality	(4) Thyroid volume	(6) Costs
Trial limitations (risk of bias)a	Was random sequence generation used (i.e. no potential for selection bias)?	Unclear	Unclear	Unclear	Unclear	Unclear	Not reported
	Was allocation concealment used (i.e. no potential for selection bias)?	Unclear	Unclear	Unclear	Unclear	Unclear
	Was there blinding of participants and personnel (i.e. no potential for performance bias), or outcome not likely to be influenced by lack of blinding?	Yes (participants)	Yes	Yes	Yes	Yes
	Was there blinding of outcome assessment (i.e. no potential for detection bias), or was outcome measurement not likely to be influenced by lack of blinding?	Yes (participants)	Yes	Yes	Yes	Yes
	Was an objective outcome used?	Yes	Yes	Yes	Yes	Yes
	Were more than 80% of participants enrolled in trials included in the analysis (i.e. no potential reporting bias)?e	Yes	Yes	Yes	Yes	Yes
	Were data reported consistently for the outcome of interest (i.e. no potential selective reporting)?	Yes	Yes	Yes	Yes	Yes
	No other biases reported (i.e. no potential of other bias)?	Yes	Yes	Yes	Yes	Yes
	Did the trials end up as scheduled (i.e. not stopped early)?	Yes	Yes	Yes	Yes	Yes
Inconsistencyb	Point estimates did not vary widely?	NA	Yes	Yes	NA	Yes
	To what extent did confidence intervals overlap (substantial: all confidence intervals overlap at least one of the included studies point estimate; some: confidence intervals overlap but not all overlap at least one point estimate; no: at least one outlier: where the confidence interval of some of the studies do not overlap with those of most included studies)?	NA	Substantial	Substantial	NA	Substantial
	Was the direction of effect consistent?	NA	Yes	Yes	NA	Yes
	What was the magnitude of statistical heterogeneity (as measured by I²) ‐ low (I² < 40%), moderate (I² 40% to 60%), high I² > 60%)?	NA	Low	Low	NA	High (↓)
	Was the test for heterogeneity statistically significant (P < 0.1)?	NA	Not statistically significant	Not statistically significant	NA	Statistically significant (↓)
Indirectness	Were the populations in included studies applicable to the decision context?	Highly applicable	Highly applicable	Highly applicable	Highly applicable	Highly applicable
	Were the interventions in the included studies applicable to the decision context?	Highly applicable	Highly applicable	Highly applicable	Highly applicable	Highly applicable
	Was the included outcome not a surrogate outcome?	Yes	Yes	Yes	Yes	Yes
	Was the outcome timeframe sufficient?	Sufficient	Sufficient	Sufficient	Sufficient	Sufficient
	Were the conclusions based on direct comparisons?	Yes	Yes	Yes	Yes	Yes
Imprecisionc	Was the confidence interval for the pooled estimate not consistent with benefit and harm?	NA	Yes	No (↓)	NA	Yes
	What is the magnitude of the median sample size (high: 300 participants, intermediate: 100 to 300 participants, low: < 100 participants)?e	Low (↓)	Low (↓)	Low (↓)	Low (↓)	Low (↓)
	What was the magnitude of the number of included studies (large: > 10 studies, moderate: 5 to 10 studies, small: < 5 studies)?e	Small (↓)	Moderate	Moderate	Moderate	Moderate
	Was the outcome a common event (e.g. occurs more than 1/100)?	NA	Yes	Yes	NA	NA
Publication biasd	Was a comprehensive search conducted?	Yes	Yes	Yes	Yes	Yes
	Was grey literature searched?	Yes	Yes	Yes	Yes	Yes
	Were no restrictions applied to study selection on the basis of language?	Yes	Yes	Yes	Yes	Yes
	There was no industry influence on studies included in the review?	No (↓)	No (↓)	No (↓)	No (↓)	No (↓)
	There was no evidence of funnel plot asymmetry?	NA	NA	NA	NA	NA
	There was no discrepancy in findings between published and unpublished trials?	Unclear	Unclear	Unclear	Unclear	Unclear
aQuestions on risk of bias are answered in relation to the majority of the aggregated evidence in the meta‐analysis rather than to individual trials. bQuestions on inconsistency are primarily based on visual assessment of forest plots and the statistical quantification of heterogeneity based on I². cWhen judging the width of the confidence interval, it is recommended that one uses a clinical decision threshold to assess whether the imprecision is clinically meaningful. dQuestions address comprehensiveness of the search strategy, industry influence, funnel plot asymmetry, and discrepancies between published and unpublished trials. eDepends on the context of the systematic review area. (↓): key item for potential downgrading the certainty of the evidence (GRADE), as shown in the footnotes of the summary of findings table(s); NA: not applicable