The pros and cons of calming agents

The pros and cons of common calming agents used in show horses.

We have all experienced the spookier than normal horse, or the equine that gets too anxious at shows. If you are the lucky owner of one of these horses, like I am, you have probably asked yourself: Is there anything more I can do to calm him down?

This is a pretty common problem as evidenced by the number of so-called calming agents available. Plenty of them are oral supplements, but there are also some injectable substances that have recently come under scrutiny in the news (and rightfully so).

Oral calming agents

Many products fall into this category. The main ingredients include minerals (magnesium), vitamins (B vitamins, such as inositol and thiamine), amino acids (l-tryptophan, taurine, amino propanoic acid), herbs (valerian root, chamomile, passion flower, oat pods, skullcap, etc), and flower essences (Five Flower Formula, Rescue Remedy, etc). I also include essential oils here as they are sometimes taken internally, but more often they are used for aromatherapeutic purposes (lavender, chamomile, bergamont and jasmine, to name a few!).

It has been my experience, as well as that of several equine nutrition specialists, that supplementation of vitamins and minerals only has a calming effect in horses that are deficient in those nutrients. This is why the first thing I recommend when a client asks me about using calming agents is to take a good look at your nutrition program. Horses that are receiving good quality hay with a vitamin/mineral ration balancer formulated for your geographical region will not be deficient in magnesium or B vitamins in the first place.

Vitamins and minerals

Symptoms of magnesium deficiency include hyper-excitability and muscle cramping, which is why the manufacturers of calming products include this mineral in their formulations. Symptoms of vitamin B deficiency are quite varied because of their role in so many of the body’s systems, but normally include gastrointestinal signs such as diarrhea (particularly vitamin B1/thiamine deficiency because of its important role in carbohydrate metabolism) as well as nervous system effects.

But as I stated above, horses eating good quality hay along with a ration balancer will not be deficient in these vitamins or minerals. One exception is a horse that has a malfunctioning hindgut. This is because the bacteria in the hindgut manufacture almost all the B vitamins the horse needs, but if the hindgut is not functioning properly, as in horses with colonic ulcers, B vitamin production may be diminished.

Amino acids

The basis for giving extra “calming” amino acids to horses is centered upon their known effects in people. But we need to remember that the horse’s digestive system is different from a human’s, so horses absorb these amino acids at a different rate than we do. The horse is able to synthesize many amino acids from building blocks they receive from proper nutrition, and those they cannot make themselves they will get through high quality forage.

L-tryptophan is converted to serotonin (a neurotransmitter) in the body through complex biochemical reactions. It is thought that increased serotonin levels in horses will act the same way they do in people and have an anxiolytic effect. There have been a few studies looking at the effects of l-tryptophan in horses, but they all show no change in behavior after consuming levels of l-tryptophan commonly found in commercial supplements. Also, doses lower than what is found in these supplements actually caused the study horses to become mildly excited! And high doses reduce a horse’s endurance capacity and can cause acute hemolytic anemia.

Taurine seems to calm the sympathetic nervous system in people, but again this has not been studied in horses. The sympathetic nervous system is the part that responds to stress (fight or flight). Amino propanoic acid, also known as beta– Alanine, has been shown to have anxiolytic effects in mice, but I cannot find any research specific to horses.

Herbs, flower essences and essential oils

Herbal preparations work for some horses, but not every herb works for every horse, and many of these products are now prohibited by the FEI and USEF as performance-enhancing substances. If you are interested in trying an herbal supplement for your horse, I suggest you discuss available options with an integrative veterinarian so the correct herbs for your particular horse in your particular situation are chosen. Flower essences, on the other hand, can be safely used in all animals chill out as they work on an energetic level and will not test positive. I have also found the aromatherapeutic use of essential oils to be very effective in animals.

Injectable calming agents

Injectable sedatives/tranquilizers include Diazepam (valium), Reserpine (Rakelin), Xylazine (Rompun), Detomidine (Dormosedan) and Acepromazine; neurotransmitters (gamma amino butyric acid (GABA), Gabapentin); and various other human anxiolytics and anti-psychotics.

Two of the most worrisome calming agents readily available on the lay market are injectable magnesium sulfate and GABA (the main ingredient of “Carolina Gold”). Both were added to the FEI and USEF prohibited substances lists earlier this year because of their potential side effects.

• Injection of magnesium sulfate does have a profound calming effect, but there is a small margin of safety when it’s administered intravenously, as it has sedating effects on both muscles and the heart. If too much of this drug is given, or if it’s given too fast, it will affect the horse’s heart rate and rhythm, causing him to collapse and most likely die.

• GABA acts as an inhibitory neurotransmitter when administered intravenously and therefore has the potential to be anxiolytic, analgesic, anticonvulsant and sedative. Adverse side effects include dizziness, fatigue and drowsiness. I would not want to ask a horse that was administered this drug to perform, let alone get on his back! This is a very risky undertaking by competitors who are more concerned about winning their next ribbon than their horses’ welfare.

Legalities and ethics

No drug (or herb, for that matter) can be given without the potential for side effects. If you are considering the use of a calming agent in your horse, I cannot stress enough that you should get your veterinarian involved. There are many reasons for a horse to be hyper-excitable, including an excess of caloric intake, lack of exercise and pain, as well as improper or inadequate training. Your veterinarian will be able to rule out pain, go over your nutrition plan, and give advice on calming agents that can be used safely and legally. Above all, the welfare of our horses has to come first.

Injectable sedatives/tranquilizers should only be used under direct veterinary supervision during medical procedures (such as dentistry or wound repair). They have a fine margin of safety, and produce effects in the horse that make him unsafe to ride. Certain tranquilizers may be prescribed by your veterinarian to keep a horse calm on stall rest, and should only be used for that purpose as directed. 


Dr. Kelli Taylor is a 2008 summa cum laude graduate of Washington State University’s College of Veterinary Medicine. She was born with a love of horses and has striven to be near them her entire life, even when it was impossible for her to have her own. Just after graduation, she completed an internship in Equine Medicine and Surgery at Pilchuck Veterinary Hospital in Snohomish, Washington and obtained certification in animal chiropractic through the IVCA. She will be completing her certification in veterinary acupuncture this year. Dr. Kelli is very excited to be announcing the opening of her own mobile veterinary chiropractic and acupuncture practice in Washington State this winter. When not working, you can find Dr.Taylor trail riding or hiking with her husband in the great outdoors of the Pacific Northwest. She can be reached via e-mail at