Based on NIH | Does levothyroxine contain pork-derived ingredients, and is there any side effect risk for patients with pork allergies or who avoid pork for religious reasons?

Most levothyroxine products do not contain pork-derived active ingredients, but some formulations may include animal‑derived gelatin in the capsule shell, and “natural desiccated thyroid” products (which are different from levothyroxine) are made from pig thyroid. If you avoid pork for religious reasons or have a pork/gelatin allergy, there are levothyroxine options that are likely acceptable, but you should choose the right formulation. ^{[1] [2] [3]}

Key points at a glance

• Synthetic levothyroxine tablets: The active drug is fully synthetic (not from pork). Some tablet brands list excipients like croscarmellose sodium, mannitol, maltodextrin, and may list “gelatin (unspecified)” among inactive ingredients depending on manufacturer and strength. “Unspecified gelatin” can be animal‑derived (often bovine or porcine) and may not be suitable for strict pork avoidance or gelatin allergy. ^[4]
• Levothyroxine capsules (softgels): Several U.S. softgel capsule products list gelatin, glycerin, and water as the capsule excipients; the gelatin source is not specified in the label. Gelatin in capsules is typically animal‑derived and can be porcine or bovine. ^{[1] [2]}
• Natural desiccated thyroid (NDT) products (e.g., NP Thyroid, “thyroid, porcine”) are explicitly derived from pig thyroid and therefore contain pork. These are not levothyroxine; they contain both T4 and T3 from porcine glands and are not suitable for those avoiding pork. ^{[5] [3]}

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Does levothyroxine contain pork?

• Active ingredient: Levothyroxine (T4) itself is a synthetic molecule and is not pork‑derived. This applies across brands and generics.
• Inactive ingredients vary by product:
  • Some tablet presentations list excipients that include “gelatin, unspecified,” indicating potential animal origin. This means certain levothyroxine tablets might include animal‑derived gelatin. ^[4]
  • Softgel capsule products list gelatin as an inactive ingredient without specifying the animal source. This gelatin may be porcine. ^{[1] [2]}
  • In contrast, NDT products (not levothyroxine) are explicitly porcine thyroid tissue. These are pork‑derived by design. ^{[5] [3]}

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Allergy and religious considerations

• Pork allergy risk:
  • True IgE‑mediated allergy to pork is uncommon; however, reactions to animal‑derived gelatin are documented in other contexts. Because some levothyroxine forms use gelatin, a person with a known gelatin allergy may be at risk and should avoid gelatin‑containing capsules/tablets. ^{[1] [2]}
  • If you have a history of reactions to gelatin or to capsule shells, a gelatin‑free tablet formulation is a reasonable alternative. Some tablet strengths and manufacturers avoid gelatin; check the specific product label. ^[4]
• Religious or dietary avoidance of pork:
  • Avoid NDT products labeled as “thyroid, porcine” if you avoid pork. ^{[5] [3]}
  • Levothyroxine tablets without animal‑derived excipients are typically acceptable; however, confirm that the specific brand/strength does not list gelatin. Softgel capsules that list gelatin may be porcine‑derived and may not align with religious restrictions unless manufacturer certifies a non‑porcine source. ^{[1] [2] [4]}

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How to choose a suitable product

• Prefer tablet formulations with clear excipient lists: Review the exact National Drug Code (NDC) and strength; excipients can differ by strength and manufacturer. Select a tablet that does not list gelatin among inactive ingredients when pork/gelatin avoidance is needed. ^[4]
• Be cautious with softgels: Softgel levothyroxine lists gelatin as an excipient, source unspecified; if religious constraints or gelatin allergy exist, consider a non‑gelatin tablet instead. ^{[1] [2]}
• Avoid natural desiccated thyroid: Products such as NP Thyroid or “thyroid, porcine” are directly derived from pigs and should be avoided if you cannot take pork. ^{[5] [3]}

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Examples from official labels

• A levothyroxine capsule label lists inactive ingredients as gelatin, glycerin, and water, without stating the animal source. This implies animal gelatin is present. ^{[1] [2] [6] [7] [8]}
• A levothyroxine tablet product lists inactive ingredients including “gelatin, unspecified” on certain strengths, showing that some tablet presentations can also contain gelatin. Always verify your specific manufacturer and strength. ^[4]
• NP Thyroid and similar NDT labels state they are natural preparations derived from porcine thyroid glands, confirming pork origin. These are not the same as synthetic levothyroxine. ^{[5] [3]}

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Practical tips

• Ask your pharmacist to dispense a gelatin‑free levothyroxine tablet and to document the NDC they provide so you can consistently receive the same formulation. Inactive ingredients may vary among manufacturers and tablet strengths. ^[4]
• If you currently take a softgel levothyroxine, discuss switching to a tablet that does not list gelatin if you have religious restrictions or a suspected gelatin allergy. This change typically does not affect the active ingredient but may require a TSH recheck after 6–8 weeks, as with any levothyroxine brand switch.
• If a clinician has suggested NDT (porcine) products, and you avoid pork, ask about staying with synthetic levothyroxine instead. NDT is explicitly pork-derived. ^{[5] [3]}

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Bottom line

• Levothyroxine (the drug) is synthetic and not pork‑derived, but some levothyroxine products especially softgel capsules contain animal‑derived gelatin as an inactive ingredient. For those avoiding pork or with gelatin allergy, a gelatin‑free levothyroxine tablet is generally available and preferred, while natural desiccated thyroid (porcine) should be avoided. ^{[1] [2] [4] [5] [3]}