In some horse federations, capsaicin is banned. I think it would depend upon what drugs the AMHA or AMHR are testing for now days.
Here is a news article:
[SIZE=24pt]Horsejumping painkiller banned[/SIZE]
PARIS (AFP) – The International Equestrian Federation's (FEI) veterinary commission said Wednesday it has decided to list capsaicin-based analgesic, used as a painkiller but also as a means of cajoling horses into jumping, as a formally banned substance.
Capsaicin, which can be rubbed in as a lotion to ease pain and is a derivative of the chilli pepper plant, showed up in four Beijing Games cases.
In addition to its painkilling properties capsaicin can increase sensitivity.
When smeared on the horses they suffer a burning sensation if they fail to clear the showjump bars, the idea being that they will strain themselves to jump higher and in doing so avoid the burning.
During the Summer Games, four riders were suspended after their horses tested positive for capsaicin.
Three have already been handed suspensions and fines although it has not been proved that they deliberately set out to "dope" their mounts.
Norwegian bronze medalist Tony Andre Hansen is awaiting a judgement on his case and, additionally, Brazil's Rodrigo Pessoa, a 2004 individual jumping champion, was banned after his mount tested positive for nonivamide, a banned pain reliever.