I had a yearling on layup following tendon surgery. He was becoming a menace to everyone, including himself, and the day was soon to come when I was supposed to start handwalking (oh joy). We put him on Reserpine. Oral - not injectable (which I believe is getting harder to come by). This was about 4 years ago.
The vet was very specific with me that there were side effects (diarrhea, depression, etc.) and that the drug was not approved for competition use (I have a barn full of horses so maybe he thought I might try?) etc. The yearling had to be on the oral for 3-4 days before there would be a noticeable effect (BTW - the little sweetheart ended up being totally resistant to any calming effects although he did get the runs - he also blew through Ace and dormosedan).
In any event - I would wonder if they couldn’t tell from the bloodwork whether it was likely that the horse had only received a single oral dose (which would not have been likely to do much according to both my pharmacist and mmy vet)or had repeated doses. A single oral dose would not have been much.
I will say that it is easy to mix up supplements sometimes and to double dose too. But I don’t think I have ever given actual MEDS to any horse that was not supposed to get them. I’m not perfect by any means - but medications are medications - not supplements. THey are not a day in day out thing and they have side effects. It is usually an “out of the ordinary” thing for a horse to get meds, and an “ordinary” thing for a horse to get supplements.
I might screw up and miss a dosing of meds but I never gave them to the wrong horse. If they were meds that had side effects too, and I was showing, well those are things that make you pretty careful. I mean, how many parents give actual medicine to the wrong child? THe insulin to the kid who is not diabetic? It does seem odd that so many riders seem to be having this problem. NOT giving the prescribed horse it’s meds and giving restricted meds to a horse that is not supposed to have them.
OTOH, I think a large number of people get sick or die in the hospitals every year for the same reason - so I am not casting stones.
BTW - I think routine sampling of all winners - followed by random testing, would be a great idea.