A CalmSolution
Herbs maybe a far better alternative for treating the nervous equine they can often effect a permanent change in temperament, and many can be legal for competition.
Herbs nourish, strengthen and re-balance the nervous system so that once an anxious equine calms down they will no longer react to things around them.
In dealing with nervous disorders, there are no 'magic' quick fixes.
In treating an equine that has a nervous temperament, it's very important to look at the equine's whole history both health and past experiences such as training, traumas, etc.... 
It ís is not advisable to attempt to treat an equine with severe problems without professional advice, but if an equines nervousness is due to a slight imbalance, feeding a mix of herbs will usually effect a long-term solution.
There is a class of herbs called 'nervine' herbs that have specific actions on the nervous system. Many of the nervines contain high levels of magnesium phosphate a mineral that has been found to be very important to the health and well being of nerves. Different nervines nourish different aspects of the nervous system.
An equine will not always fit exactly into just one nervous system type they will often show the major signs of one type, and some signs of one or more of the other types.