Fluphenazine (Prolixen(r)), a long acting phenothiazine derivative, has not been widely adopted by the veterinary community. Nevertheless, it has found a somewhat nefarious role in the sport horse industry.
Trainers have used the drug to dull a poorly behaved horse before a sale or to "take the edge off" an excitable racehorse. The four to six week duration of action of the drug, extrapolated from the human literature, seems to suit these less than moral applications.
However, side effects and adverse reactions are common with fluphenazine, due in no small part to the lack of consensus over what constitutes an appropriate dose in the horse. How an individual suddenly finding himself in possession of fluphenazine may decide upon a dose is an interesting question, although I suspect that basic arithmetic forms no part of the answer.
The adverse reaction experienced by some horses under the influence of fluphenazine is characteristic of human Parkinsonism: rhythmic muscle tremors, rigidity, restlessness and agitation. I have witnessed a single case of fluphenazine toxicity in an equine patient. The horse spent large portions of the day either weight bearing upon its haunches, in a dogsitting position, or flexed at the knees with its hindquarters elevated, like a massive praying mantis. Although this horse spent hours, trancelike, in these positions, it should be noted that neither of these postures is ever adopted by any horse within the scope of normal, irrespective of how broadly normality is defined. Prey animals aren't afforded the luxury of looking foolish.