See the DrugPatentWatch profile for synthroid
What inactive ingredients (excipients) are in Synthroid tablets?
Synthroid (levothyroxine sodium) tablets contain the active ingredient levothyroxine sodium plus inactive ingredients used to stabilize the tablet and help it break down in the gut. The exact list can vary by tablet strength.
Common inactive ingredients reported for Synthroid tablets include binders/fillers and tablet components such as:
- Lactose monohydrate
- Cellulose (microcrystalline)
- Corn starch
- Croscarmellose sodium
- Magnesium stearate
- Other components used for tablet formulation and, in some strengths, color/film-forming ingredients
Because inactive ingredients can differ by strength (for example, based on color additives and manufacturing formulation updates), the only reliable way to confirm the precise inactive ingredient list for the dose you take is to check the specific package insert for your exact Synthroid strength and lot.
Does Synthroid have lactose? Is it gluten-free?
Many levothyroxine formulations used in thyroid replacement contain lactose as an inactive ingredient (often as lactose monohydrate). If you have lactose intolerance or other excipient sensitivities, verify your specific Synthroid strength in the package labeling.
On gluten-free status: whether Synthroid is “gluten-free” is a separate question from whether it contains gluten ingredients; you need to check the product labeling or manufacturer documentation for the specific product/strength.
Why can the inactive ingredients differ between tablet strengths?
Synthroid tablets come in multiple strengths, and manufacturers may use different tablet colors and corresponding excipients at different strengths. Even when the active ingredient stays the same (levothyroxine sodium), the inactive-ingredient profile can change.
To avoid mistakes, look up the inactive ingredients for your exact strength (for example, 25 mcg vs 100 mcg), since ingredient lists may not be identical across strengths.
Where to find the exact inactive-ingredient list for your Synthroid strength
The most accurate source is:
- Your Synthroid prescribing information/package insert for that specific strength (and sometimes the current manufacturer labeling).
If you tell me the strength on your bottle (e.g., 50 mcg, 112 mcg, 175 mcg), I can help you pinpoint what to look for on the package insert for that exact tablet.