Pergolide mesylate (Prascend) is used to treat pituitary pars intermedia disfunction (PPID) in horses. PPID is not associated with a primary thyroid disorder. However, it is part of the non-thyroid illness syndrome, noted François-René Bertin, DVM, PhD, of Purdue University.

Bertin presented at the 2025 Global Equine Endocrine Society (GEES) meeting. His presentation was titled “The effect of pergolide mesylate on blood thyroid concentrations and thyroid function in horses.” Bertin, M.M. Jargielo, and J.E. Kritchevsky, all of Purdue, authored the research.

Aims of the Study

Pergolide is labelled for the treatment of PPID, said Bertin. He noted that it is “over 90% protein bound. As such, it could cause a decrease in thyroid hormone concentrations by displacing them off circulating proteins.”

The aim of the Purdue study was to determine the effect of pergolide administration on horses’ thyroid function.

The Pergolide Study

Researchers used six light breed horses in the study (17–24 years old, 530–599 kg or 1,169-1,361 pounds). Each received 1 mg of pergolide mesylate orally once a day for 5 days. Total thyroxine (tT4) was measured daily from Day 0 to 11 (before, during, and after pergolide treatment).

Thyrotropin-releasing hormone (TRH) stimulation tests were conducted on Days 0 and 6, said Bertin. “Total triiodothyronine (tT3), tT4, and free thyroxine by equilibrium dialysis (fT4) were measured at baseline, 2 hours (tT3), and 4 hours (tT3, T4, and fT4) after TRH administration. Effect of pergolide administration on thyroid hormone concentration was determined by analyses of variance, with p < 0.05 considered significant.”

Results

Pergolide administration had no detected effects on tT4 during and after treatment, said Bertin.

Administration of TRH resulted in a significant increase in all thyroid hormones. However, pergolide had no significant effect on thyroid function.

Conclusions

“Pergolide has no detected effect on thyroid hormone concentrations or thyroid gland function in horses,” Bertin concluded. He said that protein-bound agents do not necessarily affect blood T4 concentrations.

He went on to say that low thyroid hormone concentrations in PPID horses are unlikely to be caused by pergolide.

Further Reading

  • Kimberly S. Brown and Jewell

    Kimberly S. Brown is an award-winning writer and publisher. She is the Editorial Director for My Senior Horse. Brown spent 10 years at Equine Network, parent company of My Senior Horse. Prior to that she worked for three years in equine nutrition after she retired from nearly 30 years working at The Blood-Horse. Brown spent the last 15 years of her time at that organization creating and developing The Horse and TheHorse.com.

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