L-Tryptophan calmers, thoughts?


Well-Known Member
22 July 2021
I am interested to know peoples opinions on L-Tryptophan as I feel that there is a lot of contradicting information on it.

It is said to produce serotonin which in turn has a calming effect. However, when used on horses, they say it has the opposite result and increases heart rate/excitability. I am interested in knowing how this differs from human to horse.

Would love to know everyone else's thoughts on it.


Well-Known Member
2 January 2012
I have never heard that before and would have thought that the action of neurotransmitters (eg serotonin) would be similar in all mammals, so humans and horses.

I used to use Super So Kalm which contains L-Tryptophan on my sharp warmblood and it definitely helped him, when straight magnesium calmers didn't, so I do think it works.


Well-Known Member
14 September 2010
I did use a calmer with L-Tryptophan (Nutri Science anxicalm) and did find it beneficial but I read the same thing about L-Tryptophan so changed to Science Supplements ProKalm which doesnt have it, which I did find much better but I cant say that the other one was awful! I think it can depend on the horse and how they react when stressed possibly so it might be like supplement helps one person but another person finds it useless?!

I think Magnesium has definitely been proven only to work for horses with a proven deficiency though but I'm still on the fence about L-Tryptophan!


Well-Known Member
23 November 2019
It is very dose-dependant, which depends on the individual horse’s ability to convert tryptophan to serotonin. I took the supplement myself and found i converted it effectively and quickly so that even a small dose (for a human) caused me to have ’serotonin syndrome’ symptoms - which then resulted in me becoming extremely hyper-sensitive, fast heart, anxious, then i felt very verrrry sleepy and slept for hourse - this was within an hour of taking l-tryptophan. I never dared try it again!

Melatonin converts to tryptophan which then converts to serotonin. Melatonin is made in the brain ONLY during pitch black dark - so when we sleep as humans IF in a pitch black room we make this neurotransmitter, which then goes on to make the others mentioned.
A horse more than likely makes more melatonin in the winter due to much longer dark nights than summer. Bear in mind that moon light would inhibit melatonin production.
So any indoor ‘american’ barn systems that have lights on at night are no good from this perspective. Any lights on at night throughout the night in/around stabling is cause for concern regarding equine neurotransmitter health.

It’s a known phenomenon that for us to stay awake, without dark rest, within 3 days a human can easily experience psychosis. Its not just lack of sleep that causes it, its also the lack of dark, closed eyes, dark room - melatonin production - without this it induces such odd mental experiences for us. Imagine a horse , being a flight prey creature experiencing this environmental stress: no where to lay down for REM sleep, no place that is ever pitch black due to yard lighting -no wonder the equine calmer supplement industry is constantly expanding. Mild psychosis is what we would call in a horse ‘sharp behaviour/ spooking easily’.

I personally wouldnt use neurotransmitter supplementation on horses at all - as its tricky enough to treat humans, and they can relay verbal feedback, whereas a horse can only display changed behaviour. Dosage is critical and horses are very sensitive. There’s a risk also that external supplementation in any mammal will then cause the body to stop producing it within naturally, due to measuring it coming from an external source.
I’d focus instead on vitamin/mineral balancing only, as neurotransmitters require certain nutrients to be present in the body, to actually form those neurotransmitters. So nutritional balancing has the natural side effect of helping the body produce the more tricky/volatile endocrine /neuro substances, without us having to guess and mess around with supplementing them directly and going through a potentially confusing journey.

“serotonin syndrome (SS) is a group of symptoms that may occur with the use of certain serotonergic medications or drugs.[1] The degree of symptoms can range from mild to severe, including a potentiality of death.[4][5][2] Symptoms in mild cases include high blood pressure and a fast heart rate; usually without a fever.[2] Symptoms in moderate cases include high body temperature, agitation, increased reflexes, tremor, sweating, dilated pupils, and diarrhea.[1][2] In severe cases body temperature can increase to greater than 41.1 °C (106.0 °F).[2] Complications may include seizures and extensive muscle breakdown.[2]

Serotonin syndrome is typically caused by the use of two or more serotonergic medications or drugs.[2] This may include selective serotonin reuptake inhibitor (SSRI), serotonin norepinephrine reuptake inhibitor (SNRI), monoamine oxidase inhibitor (MAOI), tricyclic antidepressants (TCAs), amphetamines, pethidine (meperidine), tramadol, dextromethorphan, buspirone, L-tryptophan, 5-HTP, St. John's wort, triptans, ecstasy (MDMA), metoclopramide, or cocaine.[2] It occurs in about 15% of SSRI overdoses.[3] It is a predictable consequence of excess serotonin on the central nervous system (CNS).[6] Onset of symptoms is typically within a day of the extra serotonin”



Well-Known Member
15 March 2016
I don't know the science behind it, but I suspect I saw the same social media post as triggered this. I'm always a bit dubious about the source considering they have their own products to sell and market.
I've not had any call to use calmers for a long time, but I do feed magnesium as it seems to help Charlie's mallanders. I've noticed no change in his behaviour with or without it - which from all I've read shouldn't be the case at all.
Personally, and this is just my opinion I think its a bit like antidepressants for humans. There's more goes on in the brain than we know or understand and something that works one way for one person may work very differently.