It depends on who makes it. Amneal lists lactose in its tablets. The other manufacturers shown here don’t.

Check the company name on your bottle. Two prescriptions can both say levothyroxine and contain different fillers. [1][12][13][19][20][21][22][23][24]

Your pharmacy may have switched manufacturers. You can still be taking 100 mcg of levothyroxine while getting a different set of fillers and dyes.

Start by comparing the manufacturer on your old bottle with the one on your new bottle. If it changed, compare the ingredients above and write down when your symptoms started. Your thyroid labs also matter, because symptoms alone don’t tell you whether the problem is an ingredient reaction or the amount of hormone you’re absorbing. [1][12][13][9]

No. Lupin lists Blue 1 in its white 50 mcg tablet. Amneal and Alvogen list no color additives at that strength.

If you’re avoiding a dye, check the ingredients for your manufacturer and strength. A white tablet isn’t enough to go by. [1][12][13]

Look for MFR or Manufacturer on your bottle or pharmacy paperwork. If you can’t find it, your pharmacist can check which company supplied your refill.

The NDC is the number that identifies the drug and its packaging. The cards above show the product portion of that number. Your pharmacist can use the full NDC to check the right ingredient list, which is helpful if a manufacturer has changed its formula. [1][12][13]

Yes. “Inactive” means it isn’t the thyroid hormone. Fillers, binders, and dyes still come into contact with your body, and some people react to them.

Published cases describe reactions to acacia, magnesium stearate, povidone, and mannitol. If your symptoms started after a change in medication, the inactive ingredients deserve a look too. [4][5][11][14][15]

No. Microcrystalline cellulose and croscarmellose sodium are different ingredients, even though both have “cellulose” in their names.

In one published case, a patient with an allergy to carboxymethylcellulose tolerated both of those other forms. If you’ve reacted to a cellulose ingredient, write down its full name so you know what to look for on other labels. [18]

Your pharmacist can help you find another manufacturer that makes your prescribed strength. Use the comparison above to see which fillers and dyes would change.

Let your prescriber know about the switch so you can plan when to recheck your thyroid labs. Keep taking the prescribed dose unless your prescriber changes it. [1][12][13]

Manufacturers can change their formulas. Alvogen’s updated label lists Red 30 in the 112 and 175 mcg tablets, with product NDCs 47781-721 and 47781-728.

If your bottle lists different dyes, have your pharmacist check its NDC. The company name and dose may be the same even when the ingredients have changed. [13]