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How SSRIs work and why Tryptophan is superior

April 15, 2002 •

L-Tryptophan is an amino acid, one of the building blocks of protein, but unlike some amino acids, L-Tryptophan is considered essential because the body cannot manufacture its own. L-Tryptophan plays many roles in animals and humans alike, but perhaps most importantly, it is an essential precursor to a number of neurotransmitters in the brain. As such, L-Tryptophan is the only substance that can be converted into serotonin. Since serotonin, in turn, is converted in the brain into melatonin, L-Tryptophan clearly plays a role in balancing mood and sleep patterns.

Originally developed to treat depression in humans, Prozac, Zoloft, Paxil, and others are now being prescribed for a much wider variety of disorders, including anxiety, obsessive-compulsive disorder, migraine headaches, sleep disturbances, weight loss, PMS, obesity, and back pain, and the number of prescriptions for animals is growing at a similar rate.

All of these drugs work along the same principle. Selective serotonin reuptake inhibitors, or SSRI’s as they are known, work by increasing the level of serotonin (chemically called 5-hydroxytryptamine) by blocking its reuptake by adjoining neurons. Blocking the uptake of serotonin thereby leaves more in the synapse to act as a neurotransmitter.

It is a fact, however, that serotonin can also be elevated in the way nature intended, namely, by elevating serotonin’s building blocks in the diet. L-Tryptophan is the best known and most widely used nutritional supplement for this purpose. The conversion of L-Tryptophan to serotonin is a two-step process. First, L-Tryptophan is converted into 5-hydroxy L-Tryptophan, or 5-HTP, and 5-HTP is then, in turn, converted into serotonin. This is the process by which serotonin is produced from food. Unfortunately, L-Tryptophan is also the least abundant amino acid in foods. The good news, though, is that research conducted at MIT years ago established that serotonin levels can be increased by supplemental, dietary L-Tryptophan.

While animal studies are commonly used to predict the benefits of a new drug or nutrient to humans, human studies also help to point the way to improved treatments in animals. In studies done with humans on two continents by Lehman, Braverman, and Pfeiffer, depressed patients were found to have very significantly lower plasma levels of L-Tryptophan than normal controls. By way of contrast, changes in thirty other amino acids were not significant. To list just a few potential applications, human studies have also demonstrated L-Tryptophan’s benefits in treating Down’s syndrome and aggressive behavior. In parallel to human studies, a survey of horse owners reported that horses fed soy meal, which has nearly five times the level of L-Tryptophan as oats, seem less aggressive than those horses fed oats.

The question remains, how does L-Tryptophan compare with SSRI’s in treating clinical conditions? A study done by a team of Swiss and German psychiatric researchers comparing the L-Tryptophan metabolite, 5-HTP, with the SSRI, Fluvoxamine, found that depression was alleviated more predictably with 5-HTP, and while side effects are commonly reported for Fluvoxamine, the Physician’s Desk Reference does not list any for 5-HTP. The researchers went on to conclude that the L-Tryptophan metabolite actually treats a broader range of symptoms known as “serotonin deficiency syndrome,” which may manifest as depression, anxiety, sleeplessness, aggression, nervousness, obsessive-compulsive behavior, and migraines … many of the same symptoms that are being treated today in humans and animals alike with SSRI’s.

While both L-Tryptophan and 5-HTP are building blocks for serotonin, they are not identical in their action. 5-HTP, for example, is one step closer in the biochemical pathway to serotonin than is L-Tryptophan, but 5-HTP is also much more expensive to produce and narrower in its action. L-Tryptophan, in addition to being a precursor to serotonin, is also a precursor to niacin and can be used in the treatment of pellagra. It is really L-Tryptophan rather than niacin that acts as an essential vitamin. Furthermore, L-Tryptophan is an essential amino acid that plays a role in structural proteins and enzymes found throughout the body.

Whether or not deficiency symptoms exist, L-Tryptophan is clearly an essential amino acid that supports the nutritional and dietary requirements of pet and equine health. Furthermore, in the treatment of deficiency disorders, natural L-Tryptophan has clear advantages over the SSRI’s, Prozac, Zoloft, Praxil, and others, for which severe side effects continue to be documented.

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