Have Cat Questions? Ask a Cat Vet Online.
I am sorry that you have been waiting for a response. I recently just logged onto the site and noted that your question hasn't yet been answered. I am a licensed veterinarian with over 25 years’ experience and would be happy to work with you if you are still needing assistance.
A one time dose of thyroid supplementation should not usually present any significant risk. If any symptoms are seen at all, a temporary agitation and/or hyperexcitability may be seen, but I would expect by now, even if Amber did experience that, it would have worn off. Different brands of human thyroid supplements contain different levels of active thyroxine. If you let me know the brand that you are using, I can try to research it further for you, but as I have noted, since this ingestion occurred hours ago, by now, it is likely out of her system.
Please reply if you are still wanting assistance.