Tack n' Talk

Online Equestrian Resource

Does L-Tryptophan really work? Scientists say no.

A very common ingredient in many calming supplements is L-tryptophan but does this supplement really work?  There is also much confusion as to what is the tryptophan supplement.    Tryptophan is an essential amino acid, which horses are unable to manufacture themselves and require this amino acid in their diet.  The horse’s body uses tryptophan to make serotonin.  Increased levels of serotonin in the brain have been associated with sedation, increased sleepiness, reduced aggression and reduced fearfulness.

The reasoning behind of giving “extra” tryptophan” to the horse is that it should lead to an increase in serotonin level in the brain, which in turn, should have a calming effect to the horse.  However, it’s not as simple as it seems because there are a  number of factors that can influence the uptake of tryptophan by the brain, including the type and amount of fat, protein and carbohydrates in the horse’s diet.

A diet containing low levels of fat would reduce the availability of trypotophan, and conversely horses on a high carbohydrate diet may be more likely to take tryptophan into the brain.  It can also be argued that horses who are on a high carbohydrate diet can tend towards being more excitable in behaviour, so if the tryptophan would have a calming effect,  it would be more noticeable in these horses.

In a behavioral study where commercial tryptophan was fed at the recommended rate, it resulted in a no calming effect on horses, which were subjected to a standardized fear and handling test.  (J Malmkvist, JW Christensen, App Anim Behav Sci (2007) 107, 361- 366).  Tryptophan has been shown to have a somewhat calming effect in some species, however, there is little documentation or scientific evidence that it is actually effective in horses.

In a test of 28 – two year old Danish Warmblood horses wearing heart monitors and separated from their horse buddies while they were fed individually unfortunately showed that the single dose of tryptophan, at the recommended dose, had little calming effect on the these horses.  No significant differences were noted between the control and placebo group.   All the horses received similar diets and exercise except that some of the horses were fed the recommended dose of the commercial tryptophan supplement while others received a placebo.    These horses were tested 2-3 hours after being treated where two experiments were carried out.  The first test was a response of stallions to white noise to see if they were put off their feed by having a CD player close to their feed container.  In the second test, the mares were introduced into a pen that had a red and white plastic curtain close to the feed container.  The heart rate and behaviour was recorded in both tests.   (Calmatives for the excitable horse: A review of L-tryptophan.  A Grimmett, MN Sillence. Vet J (2005) 24 – 32)

The little research conducted up to 2005 on giving tryptophan to horses finds that at doses lower than those contained in commercial tryptophan supplements, horses actually become mildly excited. Whereas high doses of tryptophan also produce undesirable effects. They reduce a horse’s endurance capacity. Furthermore, high doses can be toxic if given orally, causing acute haemolytic anaemia where a metabolite in the hindgut causes red blood cells to be destroyed.

Until experiments establish a safe dose for horses, the scientists advise using non-chemical means to calm excited horses.



  Terri Hughes wrote @

I really appreciated this information. I’ve never used any calming agents or sedatives as training aids. Unfortunately, I still encounter folks who will casually use these and ACE, many times with dangerous behavorial after effects.

  tackandtalk wrote @

I know…sad how ACE is used so frequently. One really does have to wonder why?? Thanks Terri for all your kind words. – Larissa

  Carol Dunbar wrote @

Recently used a product containing L Tryptophan at a very busy, noisy show. No change in nervousness, and perhaps more nervousness in an 11 yr old gelding that is usually fairly calm.

  tackandtalk wrote @

Thanks Carol for your comment. What you have said, does agree with the scientific studies.

  moodymare wrote @

I have been using a L-Trytophan product for the past 30 days and have noticed a big difference in my mare. Normally a manic lunatic and extremely herd bound, she is now much safer to handle, anxiety and manic behaviour has been reduced, not gone completely but is now at a more manageable and less stressful level. I have tried many products, natural included, but none have produced this result. So far I have not noticed any effect to endurance or signs of anemia.

  tackandtalk wrote @

Great to hear that you found a product that works…despite the research. That’s great!

  Cathy wrote @

I have been using L-Trytophan also for jut a few days and found wonderful results from it.
I am sleeping sounder and longer and my mood level has changed from grouchy to easy to get along with.
I know my husband is glad I found this.

  vicky wrote @

i use ultra calm from smartpack it made a defrence in my horse last two rides he didnt spook or seem nervouse i it just what to make sure tryptophan is safe

  vicky wrote @

if someone knows if tryptophan is safe or is bad please let me know ive try looking for info on the web no luck

  Barb wrote @


Smart Calm has 10,000 mg of Magnesium, 550 mg of Vitamin B1, 2,000 mg of Inositol (a B vitamin relative), and 125 mg of L-Tryptophan. More than likely it’s the Magnesium that is having the calming effect on your horse. If you are concerned about the amount of Tryptophan, you can call SmartPak and speak to their nutritionist on hand.

  Isidro Galdi wrote @

Tryptophan is a great supplement if you want to boost your serotonin levels. .

<a href="My own, personal online site

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