Thyro-L Powder for Horses, slide 1 of 1

Thyro-L Powder for Horses

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Thyro-L is a powder supplement prescribed to aid in the correction of conditions associated with a low-circulating thyroid hormone in horses. It may also be helpful in the adjunct treatment for weight loss caused by insulin resistance, as well as aid in the prevention of laminitis and hyperlipidemia—an abnormally high concentration of fats or lipids in the blood.


For use in horses to help with the correction of conditions associated with low circulating thyroid hormone (hypothyroidism).

Possible Side Effects

When used as directed, no side effects have been reported. If your pet is allergic to any of the ingredients, signs of an adverse reaction may include facial swelling, hives, scratching, sudden onset of diarrhea, shock, seizures, pale gums, cold limbs, or coma. If you notice any of these signs, contact your veterinarian immediately.

Drug & Food Interactions

No known drug interactions have been reported.


Use with caution in animals with clinically significant heart disease, hypertension or other complications for which a sharply increased metabolic rate might prove hazardous. Use in pregnant mares has not been evaluated.

  1. Prescribing Information

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  • Item Number
  • For Use With
  • Generic Name
    Levothyroxine Sodium
  • Common Brand Name(s)
  • Administration Form
  • Brand
  • Product Form
  • Health Condition
  • Drug Type

Each pound (453.6 g) contains: Levothyroxine Sodium USP 0.22% (1,000 mg), and each level teaspoonful contains approximately 12 mg of T-4.

Levothyroxine Sodium, USP

Recommended Dosage

Administer exactly as described by your veterinarian. If you miss a dose, give it as soon as you remember. If it's nearly time for the next dose, you should skip the dose you missed and resume your regular schedule. Do not double dose.

Storage Instructions

Store at room temperature and protect from light. Avoid excessive heat above 104°F.


Why Trust The Pioneer?

Levothyroxine for horses was introduced by LLOYD in 1965 as iodinated casein powder, Thyrone, and was replaced with Thyro-L in 1996. LLOYD developed the Levothyroxine Sodium Powder specification monograph for USP. It is the only (levothyroxine) USP powder available for horses.

How Does Thyro-L Set A Higher Standard -For Levothyroxine Sodium Powder For Horses?

Only Thyro-L meets the higher powder, USP standard for an oral pharmaceutical powder and can make this claim on the front mast of its label. Check the label of any other T4 powder product. You will see that it only contains Levothyroxine Sodium USP as a listed ingredient [Levothyroxine Sodium USP (0.22%)], which simply indicates a type of raw material.

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  • 5 out of 5 stars

    What a Difference!

    By Lynn on Nov 5, 2020

    My new vet prescribed this for my 18 yr. old Anglo-Arab mare the very first time she evaluated her and reviewed my horse’s vet notes, earlier lab reports. She knew right away what my concerns were and what my mare needed, unlike previous, less experienced vets! My horse could have been helped 2 years earlier if I’d had my new vet on board back then! This product has already made a huge difference in my mare’s overall health, attitude and appearance after only 2 weeks! I am thrilled! Thank you!

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