The Primary Component: Porcine Thyroid Glands
At its core, Nature-Throid is a form of desiccated thyroid extract (DTE), a "natural" thyroid hormone replacement therapy. The primary active substance is sourced from the thyroid glands of pigs, making it a porcine-derived product. The process involves collecting, cleaning, drying, and powdering the animal's thyroid glands to create the raw material for the medication. This method of producing thyroid hormone replacement is one of the oldest, dating back to the late 19th century.
The Hormone Blend: T4 and T3
Unlike synthetic alternatives that typically contain only a single hormone, Nature-Throid provides a combination of both T4 (levothyroxine) and T3 (liothyronine). The formulation is standardized to provide a specific ratio of these two hormones. For example, one grain (65 mg) of thyroid contains 38 mcg of T4 and 9 mcg of T3, which is a ratio of approximately 4:1. This differs from the ratio of T4 to T3 produced by the human thyroid gland and can lead to unphysiologically high T3 levels in some patients. Some proponents also claim the medication contains trace amounts of other natural thyroid cofactors like T1, T2, and calcitonin, though the significance of these is debated.
Inactive Ingredients: Fillers and Binders
To form the finished tablet, the porcine thyroid powder is mixed with several inactive ingredients. According to product information available before its recall, these included:
- Colloidal Silicon Dioxide: A flow agent to prevent caking.
- Dicalcium Phosphate: A binding agent and filler.
- Lactose Monohydrate: A common filler and binding agent, derived from milk sugar. The amount is small, and generally tolerated by those with dairy protein allergies, but it is contraindicated for people with lactose intolerance.
- Magnesium Stearate: A lubricant that prevents the tablet mixture from sticking to the manufacturing equipment.
- Microcrystalline Cellulose: A bulking agent.
- Croscarmellose Sodium: A disintegrant, which helps the tablet dissolve in the body.
- Stearic Acid: A lubricant.
- Opadry II 85F19316 Clear: A coating to make the tablets easier to swallow and reduce odor.
Availability Issues and The Recall
In September 2020, Nature-Throid manufacturer RLC Labs issued a voluntary nationwide recall for all lots of Nature-Throid and WP Thyroid due to sub-potency. Testing revealed that the recalled tablets contained less levothyroxine (T4) than was stated on the label. In subsequent years, the brand was officially discontinued by RLC Labs. As of 2025, the FDA has also escalated enforcement actions against all unapproved animal-derived thyroid medications, including DTE products, highlighting concerns about manufacturing inconsistencies, potency, and safety.
Comparison of DTE and Synthetic Thyroid Medications
| Feature | Compounded Thyroid USP (Similar to Nature-Throid) | Synthetic Levothyroxine (e.g., Synthroid) |
|---|---|---|
| Source | Animal-derived (porcine) | Laboratory-made |
| Hormone Content | Contains both T4 and T3 | Contains only T4 (levothyroxine) |
| Hormone Ratio | Fixed ratio (~4:1 T4 to T3), unphysiologic relative to human thyroid | T4 is converted to T3 by the body, allowing for physiologic regulation |
| FDA Approval Status | Unapproved; grandfathered products are subject to enforcement action. Compounded versions have different regulatory status. | FDA-approved; meets strict standards for safety, purity, and potency. |
| Batch Consistency | Variable potency and purity have been cited by the FDA as concerns. Recalls have occurred due to potency issues. | Highly consistent dosage and potency due to strict manufacturing standards. |
| Treatment Approach | Proponents believe the T4/T3 combination provides a "more natural" replacement. | Standard of care for hypothyroidism; dose is adjusted to normalize TSH levels. |
| Therapeutic Fluctuation | T3 has a shorter half-life, causing more daily fluctuations in hormone levels. | Long half-life (about 1 week) leads to stable blood levels. |
Conclusion
Nature-Throid is made from dried, powdered thyroid glands of pigs, providing a blend of natural T4 and T3 hormones along with several inactive ingredients like lactose. Due to significant manufacturing and potency concerns that led to a full recall and brand discontinuation, it is no longer commercially available. Patients previously on Nature-Throid must now use compounded formulations containing Thyroid USP from a pharmacy or transition to an FDA-approved synthetic alternative. The ongoing regulatory scrutiny of desiccated thyroid extracts highlights the importance of discussing all treatment options with a healthcare provider to ensure safe and effective therapy for hypothyroidism.
