Does Levothyroxine Contain Pork or Come From Pigs?

Levothyroxine (the standard thyroid hormone replacement, often labeled levothyroxine sodium) used in most prescription tablets today is synthetic, not animal‑derived, and does not contain pork. Its active ingredient is chemically manufactured thyroxine (T4), and typical tablet excipients (inactive ingredients) are common pharmaceutical additives like microcrystalline cellulose, magnesium stearate, silicon dioxide, and various disintegrants or colorants depending on the brand and strength. ^{[1] [2] [3]}

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Levothyroxine vs. “Natural” Thyroid

• Levothyroxine (synthetic T4): This is the drug of choice for hypothyroidism because its effects are predictable and the dose can be precisely titrated; it is manufactured chemically and supplied as levothyroxine sodium tablets. ^[4]
• Desiccated thyroid extracts (DTE): Brand names like NP Thyroid or other “thyroid, USP” products are derived from porcine (pig) thyroid glands, and thus are pork‑based. These contain a mixture of T4 (levothyroxine) and T3 (liothyronine) in fixed ratios per “grain.” ^{[5] [6] [7]}

In other words, while desiccated thyroid products are pork‑derived, standard levothyroxine tablets are not. ^{[5] [1] [6]}

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What’s in Levothyroxine Tablets?

Formulations vary slightly by manufacturer, but the inactive ingredients commonly include:

• Microcrystalline cellulose, magnesium stearate, silicon dioxide
• Disintegrants such as sodium starch glycolate or croscarmellose sodium
• Binders like povidone; sometimes mannitol, lactose, acacia, or gelatin
• Color additives specific to tablet strength (some strengths have none)

These components are typical pharmaceutical excipients; they are not sourced from pork in standard levothyroxine products. ^{[1] [2] [8] [9] [3] [10] [11]}

Some manufacturers also note that levothyroxine tablets contain no ingredients made from gluten‑containing grains, which can be helpful for those with celiac disease or gluten sensitivity. This statement pertains to gluten and does not imply animal origin; the active T4 remains synthetic. ^{[1] [3] [12]}

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Why the Confusion Happens

The confusion usually arises because both levothyroxine and desiccated thyroid treat hypothyroidism:

• Levothyroxine sodium is a single, synthetic hormone (T4). ^[4]
• Desiccated thyroid is a natural mixture extracted from pig thyroid glands (contains T4 and T3). ^{[5] [6]}

People sometimes hear “thyroid hormone” and assume all forms come from animals, but modern levothyroxine tablets are produced synthetically and are preferred for consistent dosing and reliable lab monitoring. ^{[4] [13]}

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Practical Tips if You Avoid Pork

• If you wish to avoid any pork-derived medication, ask specifically for levothyroxine sodium tablets rather than a desiccated thyroid product. Levothyroxine tablets are synthetic. ^{[1] [4]}
• Confirm the brand and ingredient list with your pharmacist, as excipients vary; they can provide the exact product’s inactive ingredients. ^{[2] [3]}
• Be aware that products labeled “thyroid, USP,” “porcine thyroid,” or brand names like NP Thyroid are pork‑derived and not suitable if you need to avoid porcine sources. ^{[5] [6] [7]}

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Bottom Line

• Levothyroxine tablets (levothyroxine sodium): synthetic, no pork‑derived active ingredient, excipients are standard pharmaceutical additives. ^{[1] [2] [3]}
• Desiccated thyroid extracts (e.g., NP Thyroid): pork‑derived from porcine thyroid glands, contain both T4 and T3. ^{[5] [6] [7]}

For most people with hypothyroidism, synthetic levothyroxine is the preferred and pork‑free option with predictable dosing. ^{[4] [13]}