Tryptophan

Tryptophan is an amino acid, that is, a building block of protein. Dogs have to take it in with their food because their body cannot make it itself. Among other things, the body uses tryptophan to make the messenger substance serotonin. Because serotonin plays a role in mood and stress, tryptophan is often offered as a supplement against anxiety or stress. Whether this does anything for dogs is an open question.

Feed, not a medicine: In the EU and in Switzerland, L-tryptophan is authorised as a feed additive, specifically as a nutritional additive from the amino acid group, for all animal species. Tryptophan supplements for dogs are generally sold as feed, not as veterinary medicines. Feed may not be sold with the claim that it prevents, treats or cures a disease. So you should not expect a feed to treat anxiety, panic or aggression.

Important: If your dog suddenly shows severe anxiety, panic or aggression, an illness or pain may be behind it. Have your dog examined by the vet first. If your dog is receiving medicines against anxiety or human antidepressants, only give tryptophan after consulting the veterinary practice.

Why is tryptophan important?

1. Essential for the body

Tryptophan is one of the essential amino acids. Dogs need it to build protein and have to take it in with their food. A complete dog food contains tryptophan.

2. Serotonin precursor

The body can make serotonin from tryptophan. Serotonin is a messenger substance that is involved in mood, sleep and coping with stress, among other things. However, this does not automatically mean that more tryptophan in the food changes behaviour.

3. Tryptophan and behaviour: what studies show

The evidence in dogs is thin and contradictory. Tryptophan alone is not enough against anxiety. As an addition to training, there are weak indications.

• Largest study: In a double-blind study with 207 mildly anxious family dogs, a food with tryptophan showed no confirmed difference after eight weeks compared with a food without the additive.
• Smaller study: A food with tryptophan and a milk protein component (alpha-casozepine) performed better in the owners’ assessment. However, the stress hormone cortisol in the urine did not differ. It is not possible to tell from this which component had an effect. The owners did not know which food they were giving, but the study was small.
• Older study on aggression: In an older study with few dogs and one week per food, owners rated territorial aggression lower when the low-protein food contained tryptophan than without the additive. The authors only state that it might help.

How tryptophan reaches the brain, and why the ratio matters

Tryptophan shares its route into the brain with other large amino acids. They compete for the same transporters. So what matters is not just how much tryptophan is in the blood, but how much there is in relation to these other amino acids.

In a small study with five bitches, this ratio was higher for a few hours after a carbohydrate-rich meal without meat than after food with meat, because the other amino acids in the blood were lower. The tryptophan level itself did not differ. Whether this changes behaviour was not studied.

When can a tryptophan supplement make sense?

A complete dog food is enough for basic needs. An additional supplement against anxiety or stress is not supported by current evidence. If you want to try it anyway, do so only as part of a plan that you discuss with the vet, and together with training. It cannot replace either training or treatment.

Tryptophan is also found in supplements and special foods, often together with other substances.

Forms of supplement

Tryptophan is available as powder, tablets or capsules, often combined with other substances. For most of these combinations with natural products, the evidence in dogs is limited. With combination products, it is also impossible to say which component has an effect.

Amount and feeding

A general amount for dogs cannot be given. For a supplement, follow the feeding recommendation on the pack. According to the EU authorisation, feeding should take all important amino acids into account so that no imbalance arises. If your dog is on a diet food or has an illness, talk to the vet first.

Watch out for: If you notice anything unusual after starting, such as restlessness, diarrhoea or poorer eating, stop the supplement and contact the veterinary practice.

Safety and interactions

Some medicines increase the amount of serotonin in the body, for example fluoxetine or clomipramine, which are also used in dogs with anxiety disorders. Too much serotonin can trigger serotonin syndrome. The MSD Veterinary Manual names a risk of serotonin syndrome with 5-HTP, another serotonin precursor, for example when a dog gets hold of sleep aids meant for humans. Whether tryptophan in food increases the risk in dogs has not been shown.

So tell the vet which medicines and supplements your dog receives before you add tryptophan. This applies especially to medicines against anxiety or human antidepressants.

Go to the vet or animal hospital straight away: if your dog seems very restless or confused, trembles, has muscle twitches, walks unsteadily, has a fever or develops severe diarrhoea, especially if he is receiving medicines at the same time. These can be signs of serotonin syndrome.

What tryptophan cannot do

• It does not treat anxiety, panic or aggression.
• It does not replace training, habituation or counterconditioning.
• It does not replace an examination if your dog’s behaviour changes.

Fireworks: tryptophan in the anxiety plan

If your dog is afraid of fireworks or thunderstorms, plan early with the vet or a veterinary behavioural medicine practice. Supplements and special foods can at most play a supporting role there. Behaviour only changes in the long term through training, for example with gradual habituation to noises and positive association. For severe panic there are medicines, which the veterinary practice decides on.

FAQ: short answers

Is normal food enough?

For basic needs, yes. A complete dog food contains tryptophan.

Does turkey make dogs calm?

Not demonstrably. In dogs, a single meal mainly changes the ratio of amino acids in the blood; whether this makes them calmer has not been studied.

Does tryptophan help against anxiety?

This has not been shown in dogs. The largest study found no confirmed difference. If your dog is anxious, talk to the vet.

Can I give tryptophan alongside medicines?

Only after consulting the veterinary practice, especially with medicines against anxiety or human antidepressants.