Calming Supplements for Horses: Do They Really Work?

Anyone who has worked around horses knows they can be flighty. It is only natural for horses to be averse to “perceived” dangers as part of their flight (or fight) response. However, wouldn’t it be fantastic if there was a supplement that you could give any horse to help calm them down, resulting in them being less flighty? Better yet, could owners give a feed additive that could make a horse easier to train or ride? The answer is maybe, which is said with a heap of caution.

What Are Calming Supplements?

First, it is very important for anyone who competes with their horses to check their organizational guidelines. Many different horse supplements, especially those defined as “calming supplements,” have been added to many riding organizations’ banned substances lists. For example, the U.S. Equestrian Federation (USEF) has banned some substances included in many calming supplements. For example, supplements that include GABA (gamma-aminobutyric acid), also known as “Carolina Gold,” are specifically identified as a banned substance. If you compete with your horses, it is always advised to check the banned substances list before purchasing any supplements to ensure you stay in compliance.

Put simply, calming supplements are those that claim to help horses stay calmer, feel less stressed, and help horses have an overall relaxed demeanor. These supplements are made up of many natural and herbal ingredients. Some companies promise that their calming supplements help take the “edge off” and that horses will be healthier and happier.

Nutrient-based calming supplements are comprised of nutrients that are often already found in the diet of the horse, which usually are important to promote a healthy nervous system. Others are nutrients derived from natural sources. The more popular nutrient-based calming supplements are typically comprised of:

  • Magnesium. This mineral known for promoting a healthy nervous system and is thought to have an anxiety reducing effect. Deficiencies are known to lead to nervous disorders.
  • Thiamine. Also known as vitamin B-1, this is an important vitamin for nerve function in horses. Most horses are normally not deficient in thiamine, as it is produced in the hind gut. However, in low forage diets, deficiencies in thiamine can lead to nervousness, anxiety, and stress in the horse.
  • Tryptophan is an important amino acid involved in brain function and a precursor for serotonin. Serotonin has been linked to sedation-type of effect in horses and can help reduce fear or stress in horses.
  • Alpha-casozepine is a cow milk protein that is thought to have benefits for calming horses. In other species, it has shown some benefits to reducing anxiety and stress.

Herbal-based calming supplements are plants or herbs that are claimed to have calming effects on horses and help promote a healthy nervous system. Some of the more popular herbs are:

  • Valerian root is a perennial flowering plant native to Europe and Asia that is often promoted for human health as a calming supplement. It is also claimed to have calming properties in horses.  
  • Chamomile is a daisy-like flowering plant found throughout the world. It has been claimed to help in reducing anxiety, stress, and irritation in horses.
  • Ashwagandha is an evergreen shrub and member of the nightshade family that’s native to Asia and Africa. It is promoted to help reduce stress in horses and to reduce their flight response.
  • Verbena (vervain) is another flowering plant native to Europe that claims it helps to “rebalance” the nervous system of horses and helps reduce excitability and stress.

These are just a few of the ingredients that are often promoted and sold to horse owners as calming supplements.

Is There Evidence that Calming Supplements Actually Work?

The equine nutraceutical market in the United States is valued at nearly $80 million USD and is expecting substantial growth over the coming decade. This indicates that horse owners are spending their money on supplements and other alternative remedies to help their horses. Thus, they must ask themselves if their investments are sound.

When it comes to calming supplements, specifically, the research is limited, unfortunately. However, the good news is that there is scientific evidence that some of these nutrient-devised substances may help horses. In other studies, calming substances have shown very limited or no affects.

Magnesium deficiencies have been researched and have shown that there are impacts on horse nervousness, stress, and anxiety. The dangerous injectable forms (intravenous) of magnesium are known to have calming effects on horses.  However, they are banned in nearly every type of horse competition and overdoses can be lethal. When it comes to feeding magnesium, supplementation above NRC recommendations has not shown any strong evidence of having a calming effect on horses. Thus, the best advice is to ensure horses are meeting their daily NRC requirements of magnesium.

Tryptophan, as a calming supplement, has been scientifically studied in the horse. Research out of Colorado State University by Dr. Temple Grandin evaluated the effects of tryptophan on a horse’s stress levels. Data showed that short-term use of tryptophan for 1 or maybe 2 days has a slight sedative effect and might provide some benefit in stressful situations. However, longer term use, ≥ 3 days, saw the opposite affect and horses appeared more stress. The authors concluded that owners need to be cautious about using tryptophan. Other studies appear to support these findings that tryptophan has little to no effect in calming horses.

A study evaluating alpha-casozepine as a calming agent was investigated by Dr. Sue McDonnell and other researchers at the University of Pennsylvania. In their study, they did find evidence that the use of alpha-casozepine had a positive effect of calming horses during training. Yet, the product used in this study, Zylkene®, is banned by the USEF and other competition organizations. Thus, owners who compete with their horses are advised to be very cautious if using these products.

When it comes to the herbal supplements, there are no reliable, published scientific articles to show they have any effect on horses. Even more, there are very few articles detailing the effects of herbal remedies, either positive or negative, on horses. Owners are advised to be extremely cautious when feeding any type of herbal remedy to horses. Not only is there little data on how much or little to feed, but herbs can also potentially interact with any medications your horse may be on. Often the best advice equine nutritionists give is to avoid most herbal remedies or, at least, consult with your equine veterinarian prior to feeding them.

As stated, the nutraceutical market is very lucrative. Horse owners can expect to see many more supplements in the future promoting some sort of health benefit to their horses. The best advice is to keep a healthy dose of skepticism and do your research before buying any supplement for your horse.

Take Home Message

When in doubt, always speak to your veterinarian before using any supplement. You can also speak to an equine nutritionist to evaluate your feeding plan to identify any potential deficiencies (or even excesses) that may be contributing to your horse’s nervousness or excitability. For example, diets high in non-structural carbohydrates (NSC), among other issues, can contribute to a horse’s excitability. If you have any questions or concerns about what you are feeding your horses, please feel free to contact us for a free, personalized feeding plan.


Hothersal, B. et al. (2009). Role of diet and feeding in normal and stereotypic behaviors in horses. Vet Clinics of N. America: Equine Practice. 25:167-81.

McDonnell, S. et al. (2013). Calming benefits of short-term alpha-casozepine supplementation during acclimation to domestic environment and basic ground training of adult semi-feral ponies. J. Equine Vet Sci. 33:101-6.

Davis, B.P. w/Grandin T. et al. (2017). Preliminary evaluation on the effectiveness of varying doses of supplemental tryptophan as a calmative in horses. Applied Animal Behavior Sci. 188:34-41.

National Research Council. (2007). Nutrient requirement of horses. 6th rev. ed. National Academies Press.

Article By: Chris Mortensen, Ph.D.
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