It’s doable under the controlled medication rules, but the rule defines in competition approval as “exceptional” and it’s only done if the VD approves it… And you have to go through this at every event. I can see why many people do not bother because you gamble a lot if you show up at an event with your horse currently on pergolide, and then reach out to the VD to file the Veterinary Form. If the VD declines (entirely within their power), there you are, unable to complete because you haven’t taken your horse off the controlled substance prior to arriving at the event.
It’s really beyond stupid for a drug like pergolide. I hope cooler heads prevail and they give it some sort of reliable exception. And maybe in practice it’s always approved, but the rule doesn’t give that vibe.