CRD Summary: The authors said that although there was support for a conclusion that triiodothyronine enhanced and augmented serotonin reuptake inhibitors in major depressive disorder, there was no conclusive evidence. Evidence was limited and the restricted search, lack of reporting of review methods and lack of validity assessment mean that the conclusions may not be reliable.

CRD Commentary: The review question was stated. Inclusion criteria were reported for participants and intervention (triiodothyronine supplementation of serotonin reuptake inhibitors), but some studies used antidepressants other than serotonin reuptake inhibitors. Inclusion criteria were not specified for study design or outcomes. Limiting the search to English-language studies listed in two databases plus references may have resulted in the omission of other relevant studies and raised the possibility of publication and language biases. As methods used to select studies and extract data were not described, it was unknown whether efforts were made to reduce reviewer errors and bias. Although some limitations of the included studies were mentioned, study validity was not formally assessed and so results from these studies and any synthesis may not be reliable. In view of the diversity among studies, a narrative synthesis was appropriate. The authors’ conclusion about the lack of conclusive evidence appeared justified given the limitations of the evidence. However, the limited search, lack of reporting of review methods and lack of validity assessment mean that the conclusions may not be reliable.