In your opinion when is it ok to use drugs on horses?

I totally agree. Drugs should only be used if it is absolutely necessary for things like dental work, shoeing and trimming, and things that will cause harm to the horse or person if not drugged. Some people use drugs to calm the horse when there is a buyer. I think that is totally wrong! Trainers and owners should properly train their horses in the first place to get rid of unwanted behaviors, or they should twitch them in certain cases. The saddest and most necessary situation is when the animal is in pain from an injury that cannot be healed. I think that is one of the most necessary of them all considering it with help the animal to have some peace.