Inquiries from healthcare providers and patients about the gluten and aluminum content of Synthroid® (levothyroxine sodium tablets) have increased. The objective of this study was to measure and evaluate the gluten content of the raw materials used in the manufacturing of Synthroid. Additionally, this study determined the aluminum content in different strengths of Synthroid tablets by estimating the amount of aluminum in the raw materials used in the manufacturing of Synthroid.
Gluten levels of three lots of the active pharmaceutical ingredient (API) and one lot of each excipient from different vendors were examined. The ingredients in all current Synthroid formulations (strengths) were evaluated for their quantity of aluminum.
Gluten concentrations were below the lowest limit of detection (<3.0 ppm) for all tested lots of the API and excipients of Synthroid tablets. Aluminum content varied across tablet strengths (range 19–137 µg/tablet). Gluten levels of the API and excipients were found to be below the lowest level of detection and are considered gluten-free based on the US Food and Drug Administration (FDA) definition for food products. Across the various tablet strengths of Synthroid, the maximum aluminum levels were well below the FDA-determined minimal risk level for chronic oral aluminum exposure (1 mg/kg/day).
These data demonstrate that Synthroid tablets are not a source for dietary gluten and are a minimal source of aluminum.