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Tryptophan

Our Overview

L-tryptophan is an amino acid that is “essential” for both humans and other animals. The term “essential” implies that our bodies (and the bodies of our pets) cannot produce this amino acid, so it must be obtained through what we eat and what we feed our pets.

L-tryptophan is absorbed by our bodies and converted into one of two things: 5-HTP, also known as vitamin B3. Serotonin, a hormone that affects the nervous system, blood vessels, and mood, is a precursor to 5-HTP. Serotonin is known to help regulate heart and lung function, temperature, hunger, and behaviour in cats and dogs.

Studies have show that dietary supplementation of tryptophan can have promising effects on dog behaviour however studies are limited and further research would be beneficial.

Background

Niacin (vitamin B3), serotonin (5-hydroxytryptamine), and the hormone melatonin (found in the retina and pineal gland of the brain). Fish, meat (especially turkey), dairy, eggs, nuts, and wheat germ are the best sources of tryptophan. The majority of dietary tryptophan (98%) is converted into niacin.

L-tryptophan is primarily used to treat depression and related disorders. Both l-tryptophan and 5-HTP are effective antidepressants because of their ability to raise serotonin levels. 1 In some patients, l-tryptophan supplementation is as effective as antidepressant medication.

5-HTP is more likely than l-tryptophan to elevate serotonin levels and cause “serotonin syndrome” (an autonomic dysfunction characterised by neuromuscular abnormalities and altered mental state), especially when combined with other medications that elevate serotonin levels. A high-l-tryptophan diet (i.e., protein-rich foods) does not significantly increase 5-HTP levels. Synthetic l-tryptophan is produced through a glucose fermentation process, and 5-HTP is extracted from the seeds of the African shrub Griffonia simplicifolia.

Side Effects

If the contraindications and potential interactions with other medications or herbs are followed, l-tryptophan and 5-HTP are generally considered safe (described below). The U.S. Food and Drug Administration (FDA) removed tryptophan from the market in the late 1980s and early 1990s due to severe illness (eosinophilia-myalgia syndrome) and death caused by tryptophan consumption. It was later discovered that one Japanese manufacturer had used a new bacterial strain to synthesise the tryptophan, and that this bacterium had introduced toxic by-products into the supplement. Similar reactions were observed in other supplements, and it was determined that the contaminant, rather than the tryptophan, was to blame.

The most common side effects of l-tryptophan or 5-HTP are gastrointestinal symptoms (e.g., nausea, dry mouth), anxiety, dizziness, drowsiness, headache, and muscle pain. These symptoms are more common at the higher end of the dose range. People suffering from liver disease may have a reduced ability to metabolise 5-HTP. People with autoimmune diseases may be more prone to adverse reactions when taking 5-HTP, and asthmatic patients may experience an exacerbation of their symptoms.

Interactions

In patients taking medications that may raise serotonin levels (e.g., selective serotonin reuptake inhibitors, SSRIs), l-tryptophan should be used with caution (if at all). Although tryptophan may be useful in some cases when combined with SSRIs (such as fluoxetine [Prozac]) to improve the efficacy of these medications in the treatment of depression, it should be used with extreme caution to avoid serotonin syndrome. Tryptophan should not be combined with monoamine oxidase (MAO) inhibitors due to the increased risk of serotonin syndrome. Tryptophan may also be useful in enhancing the efficacy of tricyclic antidepressants (TCAs) such as clomipramine, imipramine, and amitriptyline in the treatment of depression, but it should be used with caution to avoid serotonin syndrome.

Because of the high risk of inducing serotonin syndrome, 5-HTP should be avoided in patients taking any medication that may elevate serotonin levels (SSRIs, MAO inhibitors, TCAs). Although drugs that increase serotonin levels are less common in veterinary medicine than in human medicine, several MAO inhibitors are commonly used in veterinary practise (e.g., amitraz, selegiline). Other medications that may raise serotonin levels and/or interact negatively with l-tryptophan and 5-HTP (e.g., clomipramine [Clomicalm], fluoxetine [Reconcile]) should be avoided.

Allopurinol, on the other hand, raises tryptophan levels in the brain and may be beneficial for depression when combined with supplemental tryptophan. More research and close monitoring are required when using allopurinol with dietary tryptophan. 1 Combining lithium carbonate and tryptophan raises serotonin and cortisol levels (and may require lithium dose reductions), but caution is advised to avoid serotonin syndrome and adverse cortisol changes. 1 High doses of tryptophan may interfere with the effects of diazepam clorazepate.

Tramadol works through several mechanisms, one of which is the inhibition of serotonin reuptake in the brain. The use of 5-HTP and l-tryptophan at the same time may increase the risk of side effects, including serotonin syndrome. Tramadol and 5-HTP or l-tryptophan should be administered with caution. Because of the possibility of additive negative effects, 5-HTP should be used with caution when combined with melatonin, SAMe, St. John’s wort, or tryptophan. l-tryptophan is regarded as a safer supplement than 5-HTP (i.e., it is less likely to cause significantly increased serotonin levels), whereas 5-HTP has a narrower therapeutic dose range and is much more likely to cause adverse reactions. Currently l-tryptophan is available only as a prescription medication, but 5-HTP is available as an over-the-counter supplement.

Indications

  • Acts as an antidepressant
  • Helps minimise aggression (dogs)
  • Curtails obsessive-compulsive disorder

Dose Recommendations

The daily dose of l-tryptophan should not exceed 1 g per 45 kg body weight. Toxicity is more likely when the daily dose exceeds 7 g per 68 kg per day. It may take up to 60 days before a full clinical response is seen.

The recommended dose of 5-HTP is 50–200 mg per 8–12 hr period. An increased dose or a single dose of 5-HTP at night may be
useful to enhance sleep. One clinician recommends 10 mg per kg of l-tryptophan per 12 hr period for dogs. Because of the potential for side effects and adverse reactions begin supplementation at the low end of the dose range.

Contraindications

In patients with cataracts, diabetes, psoriasis, bladder cancer, or achlorhydria (low or absent stomach acid production), l-tryptophan should be avoided. Rheumatoid arthritis may be exacerbated by l-tryptophan.

Products containing Tryptophan

Your experience with Tryptophan

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Further Reading

  1. Stargrove M, Treasure J, McKee D. Herb, nutrient, and drug interactions: clinical implications and therapeutic strategies. St Louis (MO): Mosby Elsevier; 2008:690–7, 706–17.
  2. Pizzorno J, Murray M. Textbook of natural medicine. 3rd ed. St. Louis (MO): Churchill Livingstone; 2005:1436–8.

Important Notice

The indications provided on this page are suggested uses for each supplement based upon published clinical experience and/or scientific studies. They do not represent as cures or medical treatments and should be treated as advice only. The recommended doses may be provided in human form where dosing for animals has not been established. It is imperative that you understand that this information is provided as guidelines only. You should consult with a registered veterinarian before administering any nutraceutical. Where using a marketed product you should follow the manufacturers instructions.