A nerve aid - feeding to the nervous  system. (Not another calmer - see Settle). Here is a combination of herbs which have  been used for years with success for the relieving of nervous tension, anxiety, stress.  They are classed as nervines and have a relaxing effect without causing drowsiness and will not affect performance in a detrimental way. RX has been successful in helping many headshakers. Also for damage to nerves through trauma or injury.
 'Settle' - a different combination of herbs, a liquid calmer for quicker absorption; can be given at the same time as a horse being on Relaxer in severe cases  or when extra quietness is needed, e.g clipping, travelling, times of particular anxiety or feral or traumatised horses. 
Relaxer - nerve aid is a powder added to feed twice or 3 times a day, depending on severity of condition, or mixed with water and syringed orally.