Behavior

Understanding Behavioral Medications for Horses

By Michael DePeau-Wilson

Although there are several evidence-based approaches to using medications for mental and behavioral issues, one expert said that veterinarians should consider each horse’s individual needs and avoid the same solution for every horse.

Katherine Anderson, DVM, DACVB, explained the nuances of identifying, diagnosing and treating abnormal behavioral issues in horses during a recent seminar presented by the Cornell University College of Veterinary Medicine.

“Drugs aren’t magic, and we typically pick drugs based on individual needs, so there’s really no one-size-fits-all,” said Dr. Anderson, an assistant clinical professor at Cornell. “Before you even consider a medication, you have to think about the horse. What are they doing, and what are the potential reasons why the behavior of concern is happening?”

Identifying and Diagnosing Abnormal Behavior
The most common behavioral concerns in horses are fear, anxiety, phobia, aggression and stereotypies, Dr. Anderson noted.

She explained that normal behaviors in horses can be misconstrued often as a problem because those actions are unacceptable or challenging to humans, so it is important to properly identify concerns before treating them.

While the prevalence of abnormal behavior in horses has not been well defined, Dr. Anderson said that recent studies suggest a fair estimate is that 10% to 15% of horses experience some abnormal behavior.

“[It] can get complicated when we’re trying to figure out whether or not we need to treat a problem,” Dr. Anderson said.

The first step is to understand which behaviors are abnormal. Typically, horses will begin displaying abnormal behavior in the form of discomfort during handling or work, unexpected aggression toward other horses or humans, sudden repetitive behavior such as cribbing, or even self-harm.

Any change in a horse’s behavior warrants a physical examination by a veterinarian, Dr. Anderson recommended. While these changes could be the result of behavioral issues, they can also be the first sign of physical illness as well.

“There has been a change in thinking over the past years in terms of whether a problem is medical or behavioral, and, especially in horses, it’s most often both,” she said.

For example, she noted that anxiety can also lower pain thresholds, and aggression can be the only identifiable sign of pain in horses.

Dr. Anderson highlighted several resources for identifying and measuring pain in horses, such as the Horse Grimace Scale for Pain and The Ridden Horse Pain Ethogram.

Other common medical issues that cause changes in behavior include gastric ulcers, muscle weakness, sleep deprivation, chronic neurologic diseases and cataracts or blindness, she noted.

In addition to a full physical examination, veterinarians should have some understanding of how horses learn, their overall welfare, typical human interactions and species-specific behaviors.

Choosing the Right Medication
Dr. Anderson noted that there are no medications licensed specifically for behavior in horses, so veterinarians must rely on human medications.

“We look at the side effects and the diagnoses, we extrapolate from the human side and that’s how veterinary behavior has grown to have the tools that we have, but they can only be used under the supervision of a veterinarian,” she said.

She added: “Each animal responds differently to a medication. Even if we give the same medication to 5 different animals, we might see 5 different responses.”

Some of the more effective medications available for horses are benzodiazepines, selective serotonin reuptake inhibitors (SSRIs), serotonin antagonists and reuptake inhibitors (SARIs), tricyclic antidepressants (TCAs), alpha-2 agonists, anticonvulsants and antihistamines.

Some SSRIs, such as fluoxetine, are used to affect or increase the availability of serotonin in the brain, which has been used to treat anxious, fearful and aggressive behavior in horses.

Anticonvulsant medications such as gabapentin and pregabalin can be used to treat neuropathic pain and anxiety, although gabapentin has been shown to be poorly absorbed in horses.

Benzodiazepines, such as diazepam, can be crucial in regulating anxiety, Dr. Anderson said. In addition to medications, she addressed the potential of supplements, such as cannabidiol, melatonin or magnesium. She noted that these supplements are generally less effective than medications, but some of them could offer specific benefits, such as alpha-casozepine.

In general, when deciding on a medication for a diagnosis, veterinarians should consider the problem they are trying to solve, the behavior they are seeing and the desired effect of the medication.

Medications to Avoid
Dr. Anderson also highlighted several medications, including acepromazine, reserpine, anabolic steroids, beta-blockers such as propranolol, and sympathomimetic stimulants, which may not be the best choice for horses. Drugs such as NMDA receptor antagonists and opioid antagonists such as naloxone have shown possible benefits for specific conditions, but they may not be practical or cost-effective for equine use.

In her opinion, acepromazine should not be used alone to treat anxiety—it should always be used with medications that address potential anxiety. In addition, several of these medications can cause sedation or muscle relaxation, so they should be used with caution to avoid injury, especially in riding or working horses. Many of these drugs are also not allowed by the International Federation for Equestrian Sports, she added.

Dr. Anderson also noted that reserpine—which inhibits norepinephrine, dopamine and serotonin—can also cause toxicosis. Given this concern, she noted that it doesn’t have a “place in our toolbox at this time.”

Overall, she reiterated that there is no ideal behavioral drug available for horses, and there is a lack of research investigating the available options. This means that any medications used to treat horses for behavioral issues must be individualized to the horse and supervised by a veterinarian. MeV

For more information:
Anderson, K. Behavior Medication Considerations for Horses Cornell Equine Seminar, February 2025. Cornell University College of Veterinary Medicine YouTube Channel. Accessed Feb 26, 2025.
https://www.youtube.com/watch?v=fP_dJSJtqBs

The Reading Room
Much has been written about equine behavior. Dr. Katherine Anderson recommended these articles:

Hockenhull J, Creighton E. The day-to-day management of UK leisure horses and the prevalence of owner-reported stable-related and handling behaviour problems. Anim Welf. 2015;
24:29-36. https://bit.ly/4l5phWp-MeV

Werner LC, de Oliveira GM, Daros RR, et al. Enhancing the Horse Grimace Scale (HGS): Proposed updates and anatomical descriptors for pain assessment. Vet J. 2024;307:106223. https://air.unimi.it/handle/2434/1088553

Dyson S. The Ridden Horse Pain Ethogram. Equine Vet Educ. 2022;34(7):372-380.
https://beva.onlinelibrary.wiley.com/doi/epdf/10.1111/eve.13468

Terry RL, McDonnell SM, Van Eps AW, et al. Pharmacokinetic profile and behavioral effects of gabapentin in the horse. J Vet Pharmacol Therap. 2010;33(5):485-494. https://bit.ly/4l6SjoA-MeV

McDonnell SM, Miller J, Vaala W. Calming benefit of short-term alpha-casozepine supplementation during acclimation to domestic environment and basic ground training of adult semi-feral ponies. J Equine Vet Sci. 2013;33(2):101-106. https://bit.ly/4e3edH3-MeV