How Quickly Should I Expect a Normal Range of ACTH After Starting Pergolide

Kirsten Rasmussen

Research shows that after 3 weeks on a steady dose of pergolide, ACTH stabilizes.  So you should wait at least 3 weeks after a dose change to check where you're at.  But as Dr Kellon said, the seasonal rise complicates things. 

We recommend that you adjust the dose so that ACTH is down to the mid teens to low 20s outside the seasonal rise.  Then, in July at the start of the rise check ACTH again and consider increasing the dose to keep ACTH in the mid teens to low 20s THROUGH the seasonal rise.  You can recheck ACTH in late September at peak rise to see how well you did at meeting the target ACTH, and use what you learn for the next year's dose increases.

Kirsten and Shaku (EMS + PPID) and Snickers (EMS) - 2019
Kitimat, BC, Canada
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Eleanor Kellon, VMD


There is really no way to answer your question because it's not just time but dosage that determines how well and probably how quickly it comes down; plus, the seasonal rise complicates things. The rise is over by December for most horses so your vet's plan is reasonable.  Odds are you will need to increase the dose but it will be easier to monitor after the rise.
Eleanor in PA 
EC Owner 2001
The first step to wisdom is "I don't know."


My horse started pergolide (1 pink tablet) in August (middle of the month) and was tested at the beginning of October.  She made a huge improvement in six weeks.  She went from over 1000 to 209.  But I know while this is a huge improvement, she is not where she should be yet.  The vet said because of the improvement she would keep her at 1 tablet.  I will be testing again in December.  

Should she have already been in the seasonal normal range after 6 weeks?  Is it worth a discussion to increase the dosage to bring it down quicker, if it would even do so?  What is a reasonable amount of time after being put on pergolide to expect ACTH levels to test within the seasonal norm range? 

Lisa B., Dallas (area) TX, 2022 (Lady Liberty, Mare 15 YO)