Animal & Veterinary

FDA Issues Warning Letters to Manufacturers of Unapproved Levothyroxine Drugs for Hypothyroidism in Dogs

January 29, 2016

The U.S. Food and Drug Administration has issued warning letters to six manufacturers of unapproved levothyroxine sodium drugs for hypothyroidism in dogs. These unapproved products have not been reviewed by the FDA for safety and effectiveness.

Thyro-Tabs Canine (levothyroxine sodium tablets), (NADA 141-448) is the only FDA-approved drug for replacement therapy for diminished thyroid function (commonly known as hypothyroidism) in dogs.

FDA is concerned about unapproved animal drugs. Animal drugs that have not been reviewed and approved by FDA may not meet FDA’s strict standards for safety and effectiveness. They also may not be properly manufactured or labeled.

FDA issued warning letters to manufacturers of the following unapproved levothyroxine products:

  • Thyrosyn
  • Soloxine
  • Levocrine
  • Thyromed
  • Thyroid Chewable Tablets
  • Thyrokare
  • Thyroxine L
  • Thyrovet
  • Leventa

If the companies that were issued the warning letters continue to market the violative products, they may be subject to enforcement action, including seizure of violative products and/or an injunction.

Shipments of levothyroxine active pharmaceutical ingredient (API) not referenced in an approved animal drug application or the subject of an index listing or a valid investigational use exemption and unapproved finished animal drugs containing levothyroxine offered for import may be subject to refusal.

Dog owners and veterinarians can report to the FDA any adverse events, including ineffectiveness, in dogs that received approved or unapproved hypothyroidism products. Information on reporting adverse events can be found at:

Warning Letters

Additional Information


Contact FDA

240-276-9115 FAX
Issued by: FDA, Center for Veterinary Medicine

7500 Standish Place, HFV-1

Rockville, MD 20855

Page Last Updated: 05/03/2018
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