Tryptophan Supplements for Dogs

Everyday it seems like I learn something new from pet owners. I was looking at some of the search terms people have been using to find my website and I discovered that quite a few people found my post about dog vitamins by searching for the term tryptophan supplements for dogs. Since I had never heard about giving tryptophan to dogs I decided to research the topic to learn more about it.

Can tryptophan help your
fearful or aggressive dog?

When I research any health topic about pets there’s usually four places I visit because I find them to be the most credible:

The first is PubMed which is a database that contains millions of abstracts from every medical and scientific journal you can imagine. You’re usually only given permission to read the abstract (unless you want to pay extra) but usually the abstract contains all the information you really need to know. The abstract is more or less a summary of what was discussed in the article.

The second is Medline Plus which is a service of the U.S. National Library of Medicine and the National Institutes of Health. Usually the information is directed more toward human medicine but much of the information can be applied to pets and animals as well.

The third is the Journal of the American Veterinary Medical Association. Since I’m a licensed veterinary technician I have access to all of the AVMA journals online from 2000 to the present. However, all of the abstracts are available to you on PubMed.

The fourth is my own personal library of veterinary textbooks which I’ve collected over the years as well as the textbooks we have at the clinic. I know you probably don’t have access to your own personal library of veterinary textbooks but if you’re lucky enough to live near a veterinary school the library there should have every book on animal medicine you can imagine. You probably won’t be able to check out the books but you can still oogle over them.

OK, so based on my research here’s what I learned about tryptophan and dogs:

First, it’s important to know that tryptophan is an amino acid and a very large one at that. In fact, tryptophan is the largest of all amino acids. This may not be so important if it wasn’t for the fact that tryptophan has to compete with other large amino acids for a ride across the blood brain barrier. Tryptophan is also a precursor for serotonin, so decreased amounts of tryptophan will lead to reduced formation of serotonin. This may possibly lead to more aggressive behavior in dogs. In humans, serotonin is thought to produce a “stable mood.” Tryptophan is an essential amino acid which means the body is unable to produce it so it must come from the diet.

The link between the dietary protein content found in food, metabolism of the amino acid tryptophan, and aggressive behavior in dogs has been the subject of great interest for a relatively small group of veterinarians and scientists who study animal nutrition and behavior. According to a study I found in JAVMA, for dogs with dominance aggression, the addition of tryptophan to high-protein diets or a change to a low-protein may reduce aggression. For dogs with territorial aggression, tryptophan supplementation of a low-protein diet may be helpful in reducing aggression.

It seems like with anything else, the only way to know if your dog will respond to a tryptophan supplement is to try it out for yourself. Also, if you haven’t already, I would recommend feeding your dog a low-protein diet first before supplementing with tryptophan. In another study on the effects of dietary protein on the behavior in dogs, the lowest protein levels fed to dogs was 17%.

Unfortunately, it’s impossible to accurately determine the protein level of dog food by reading the label. You may notice something listed on dog food labels called the Guaranteed Analysis. This lists the crude protein as a minimum number based on percentages. The percentage listed on the label indicates the “worst case” levels for protein in the food and does not reflect the exact amount.

For example, a dog food that has a label claim of “minimum protein 30%” cannot have less than 30% protein, but may have more. It may have 31% or 45% or 99%. We have no idea. For all we know this brand of dog food may have the same protein content as another with the claim: “minimum protein 50%”.

The crude protein level refers to a specific formula that estimates the protein content of the food by measuring nitrogen. The percentage is an index of protein quantity but does not indicate protein quality or digestibility. I clearly don’t understand why pet food manufacturers continue to print the Guaranteed Analysis on the label because all it does is confuse pet owners and gives them totally useless information. Something more useful would be the nutrition information label that is required for people food.

A more accurate way to measure the protein content of dog food is based on nutrient density, caloric distribution and “as fed” values. This topic is a little too in-depth for a blog post on tryptophan, but with a simple phone call the manufacturer of any reputable pet food company should be happy to provide you with this information. Luckily, some companies are smart and understand that a well-informed customer is the best type of customer and are starting to provide this type of information on their websites.

In terms of supplementing your dog with tryptophan, scientists studying the effects of tryptophan added 10mg/kg/meal to the low-protein diets (18%) and 12.5mg/kg/meal to the high-protein diets (30%). The dogs were also fed twice daily or approximately every 12 hours.

If you’re interested in giving your dog a tryptophan supplement I would recommend consulting with your veterinarian first. Chances are, unless they have a special interest in nutrition or behavior, they will probably wonder why you would want to do a such thing. If so, I would point them in the direction of the studies I used as references. Better yet, you might ask them for a referral to a veterinarian who specializes in behavior problems. Even though there may not be a board-certified veterinary behaviorist in your area, there are plenty of veterinarians who like to help owners with behavior problems.

Tryptophan is generally safe but may interact with other medications your dog is taking. Common side effects of supplementation include vomiting and diarrhea. Again, you should never give any medication or supplement without first consulting with your veterinarian. A blood panel and urinalysis is also recommended before starting any treatment program.


Effect of Dietary Protein Content on Behavior in Dogs
Impact of Nutrition on Canine Behavior
Effect of Dietary Protein Content and Tryptophan Supplementation on Aggressive and Hyperactive Dogs
Tryptophan Article by Dr. Dodman
Medline Plus Medical Encyclopedia

Amanda is a 2-Star Diamond Beachbody Coach, retired Licensed Veterinary Technician and RRCA certified running coach. Her geekiness is legendary and is most proud of the fact she finally found a way to turn her passions for running, fitness, nutrition, writing, and pets into a full-time business that now helps others get off the couch and get after their dreams. Proverbs 3:5-6


  1. Kristin says

    This post was very useful! I have a dog with territorial aggression. Do you know: are tryptophan supplements only available via prescription, or can I also buy them over the counter?

  2. says

    Hi Kristin, thanks for visiting and I’m glad you found my post helpful. :-) Last I checked tryptophan supplements were available OTC but I’m not sure if they’re widely available. You may want to consider finding a veterinarian in your area that specializes in behavior to help guide you along that path (most veterinarians will have no idea what you’re talking about if you bring up aggression problems and tryptophan supplements). Also, if your dog has issues with territorial aggression, one excellent book you may find helpful is MINE! by Jean Donaldson. Also, any dog behavior/training book by Jean Donaldson is excellent! Good luck!

  3. Natalie says

    Thanks Amanda, you have enlightened me today. I’ve got a young dog, who is a bit of a stresser…As well as working with a behaviourist I am seriously considering changing his food. He is 10mths old and he is eating Orijen large puppy breed with a high protein content at 50%!!!!

    I am going to change it to see if it helps him to relax and become less stressed in certain situations. He is a wonderful dog but finding on occasions he has these unpredictable stressed out moments. Can you recommend a change in food for him? I am also interested in the tryptophan supplement. Regards, Natalie.

  4. says

    Hi Natalie, I would probably wait to see what the behavorist says because they will probably know better than me! Just make sure you see a veterinarian that specializes in behavior, because there are many people who call themselves “behavorists” but they don’t have the same amount of experience and knowledge as a vet.

  5. Diana Glass says

    Hi Natalie,

    I understand dog trainer, Victoria Stilwell, recommends Tryptophan for dogs with leash aggression. She also mentions supplementing the diet with white rice and carrots, all to increase serotonin production. Could you please tell me where I can buy Tryptophan supplements? Are they available on-line and if so, what is the brand name? Also, do you have information about other foods to increase serotonin production in dogs? Thanks, Diana

  6. Diana Glass says

    Sorry to post yet another time! I forgot to mention I am in rural Italy for the next 6 mos. and cannot find a vet from whom to buy them nor an over the counter source. I have friends coming from the US who could bring them but need to know where they should go to buy over the counter.

  7. Diana Glass says

    Hi Amanda,

    My daughter in the US was able to buy the tryptophan supplements from They are also available in health food stores like GNC, etc. I spoke with my vet who said these supplements were marketed for humans but were appropriate for dogs. Vet also recommended feeding her turkey as well.

  8. says

    Amanda, thank you so much for writing this article. I found it while looking for behavior modification with diet and nutrition, looking for natural ways to help our Great Danes in rescue with their aggression and/or anxiety issues. This has helped tremendously.

  9. Michelle says

    Hello Amanda,I rescued a 6mth old Australian Cattle dog earlier this year who was severly abused. After 10 months of lots of love and patience she is comfortable around my family and is wagging her tail again but is still extremely scared beyond belief if we have visitors or if we need to take her away from our home. I am wondering if Tryptphan might help her or if you could recomend anything else as i think we need something to calm her. Many thanks, Michelle.

  10. says

    Hi Michelle, I would recommend contacting a veterinarian in your area that specializes in behavior issues. He/she will be your best source of information!

  11. Karin says

    Thanks for the informative article and references. I have a young cocker spaniel who is generally very sweet, but guards me, yes me, when I am sitting on the couch and growls to keep my other dog away. He also thinks growling and bullying is the best way to keep my other dog inline, which I have assumed was just his way of maintaining the pecking order, but now have a young mastiff puppy who is beginning to be fearful of other dogs. I need to reduce the constant growling behavior and wonder if you think a tryptophan supplement might help. I have taken my dog to obedience class and he is great, it just with my other dog.

  12. says

    It’s hard to say Karin, this may be an issue that could be resolved with training alone. Each case is a little different. Maybe something you could discuss with your veterinarian or trainer?

  13. Geraldine says

    Hi. I have a dog with fear aggression. He is aggressive towards lone men and will circle them barking. I had two behaviourists but neither recommended a change in diet. I have recently started preparing my own food for him – rice and beef/chicken/fish. Is there something I could add to the meal to help his aggression?

  14. Ivana says

    Hi Geraldine,

    I also have a young (14 mnths) fear agressive dog I rescued from Bosnia and have been trying L-tryptophan now for
    two weeks, a can really say is helping him. Must say he is mildly fear agressive, only when strange people make really strange (in his interpretation) moves or noises.

  15. Karen says

    I addi add keifer to my dogs food which has tryptophan in it. It also has other nutrients as well. Most dogs love it. A tablespoon is usually enough.

  16. Kathy Pierce says

    True Dose is a small company in St. Charles, Missouri, that makes pet supplements in a human pharmaceutical facility. They make skin and coat and joint supplements, but they also have a product called “Calming”. The main ingredients are chamomile, ginger and valerian extracts, and tryptophan. I have been using their products for several months now and am truly amazed at the difference in our dogs. We have ten dogs ranging in size from 6 lbs to 69 lbs. many are rescues with medical issues and most are 8 years or older. All are spayed/neutered and all live inside. They are family so I always call the company and question them prior to using their product. We also feed Earthborn Holistic Meadow Feast Lamb dry food supplemented with bland chicken, fruits, and veggies. You might want to check out their website

  17. Carolyn says

    Hello Amanda, thank you for your article… I was about to research Tryptophan for my Blue Heeler.

    He is on it at present because he recently damaged his second knee joint (a question of whether it is a cruciate ligament or not) within a year and the vet is insistent that we are not going to operate due to both of us ‘having a feeling’ that if we give Harry time it will finally come right -PROVIDING he is on ‘bed rest’ Oh hahaha!

    Anyway with the Tryptophan we are managing to keep him quiet and happy with very little effort at all. I give him two a day @ 26 kilos is just calming him right down.

    He is still very aware of everything around him but now chooses whether to respond or react, which is very different from rushing out mindlessly barking and not hearing me, so it seems we are getting there.

    He is now taking more directions from me because he has time to see and recognise my words or hand movements.

    You were saying about foods… Harry is allergic to the storage mite and so no grain foods for him.

    Hence I make the food for both my dogs and that means a mix of 10 grated raw vegetables (NOT onion or onion relatives) mixed in with (in Australia) roo and beef.

    The beauty of this is both dogs maintain a healthy weight with no increase over a couple of years now.

    The led me to think “If I gave up grain foods, would this help me?” I did and it did, I lost weight and now maintain a healthy weight without any effort or thought at all…

    Just thought I’d add all this as you obviously have a good following :)


  18. Jane says

    Great site and very helpful info and comments which I can relate to especially Michelle. Karen mentions Keifer – is that the same as kefir – form of yoghurt? I’ve also been advised to change the diet to a raw or semi raw mix – raw foods are amazing and not as dull as one might expect. Beyond Organic suggest that anything with more than 12 ingredients – dont eat.