What's in a calmer?

Look at the shelves in your local feed merchant and you're sure to find a vast array of different calmers. We'd always advise you to check the ingredients before buying and you'll find that there are a number of active ingredients commonly used. Below is information on a few of the common ingredients used and why. 

Do you know what ingredients are in the calmer you feed?

Do you know what ingredients are in the calmer you feed?

Magnesium aspartate

Magnesium is a common ingredient in calmers. A study in mice showed increased anxiety when their diet was deficient in magnesium. However, magnesium deficiency is rare in horses in the UK. The first scientific study to document the effect of feeding magnesium aspartate on the behaviour of horses was recently published. A slower reaction speed in horses was recorded after being fed magnesium aspartate compared with those without. However, it was unclear whether the slower reaction was a result of an effect on the brain rather than other (e.g. muscles, nerves) effects. Additionally, the horses were fed higher quantities of magnesium aspartate than you’ll find in supplements. Magnesium sulphate and magnesium oxide are commonly used in calming products, but it’s unclear whether there’s a difference in how each one effects your horse.


Tryptophan is a precursor of serotonin, known to reduce anxiety. Several studies carried out in a variety of species concluded that tryptophan reduces aggression; however this is highly variable among species and can be affected by many other factors. There’s no scientific evidence that tryptophan reduces anxiety or excitement in horses. One study focusing on the behavioural effects in horses showed mild excitement following administration. There’s currently no information on recommended or safe dose of tryptophan in horses, and side effects at higher doses have been recorded.

B Vitamins

Vitamin B6 is required to convert tryptophan to serotonin and is often found in calmers containing tryptophan. Vitamin B1 (thiamine) appeared to improve concentration and reduce excitability in humans in some studies. Evidence for their efficacy as a calmative is purely anecdotal (non-scientific). Most horses should not need additional B vitamins as they’re readily available in forage and also produced by bacteria in the hindgut.

Valerenic acid (valerian)

Valerenic acid (valerian) has no scientific backing as a calmer for horses. It’s also an FEI prohibited substance.


Your horse’s body regulates the levels of calcium in his bloodstream. A hormone called calcitonin is released in response to higher levels of calcium, which acts to maintain a consistent concentration. There’s no strong evidence to support how well calcium acts as a calmer, and studies on the behavioural responses of horses following calcium supplementation have either revealed no alteration or have been inconclusive.


This derivative of milk has been found to have a calming effect in several species. Two studies on horses indicated positive behavioural changes when fed alpha-casozepine compared with those fed a placebo. However both were based on human observation and further research is needed as neither study presented measurable outcomes.