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Source Naturals L-Tryptophan Review – 8 Reasons Why

By Sasha de Beausset Aparicio, MSc

Reviewed by Rebecca Williams, MD, MA, MB, BChir

Last Updated:

Evidence Based | Facts | Ingredients | Health Benefits | Precautions | Cost | How To Take | Conclusion

L-Tryptophan is an amino-acid based formula which promotes relaxation, restful sleep, and positive mood. It acts by supporting the synthesis of the hormones melatonin and serotonin responsible for mood and stress response and for regulating the sleep-wake cycles.Other beneficial effects refer to the immune system, circulation, digestive and nervous systems and the metabolism of foods.

Even though the product has not been evaluated by the FDA, it is advertised as a natural and tested product which meets the highest quality standards. It is commercialized as 500mg Capsules, 500g Tablets and as Powder.

The manufacturer, Source Naturals, is an American Company established in 1982. The company activates in the nutritional supplements industry and is the winner of some prestigious awards due to innovative formulations such as Life Force Multiple, Mega-Kid Multiple or Inflama-Rest.


1) L-Tryptophan Quick Facts

The main ingredient, L-Tryptophan is an amino-acid commonly used in alternative medicine for the ailments like insomnia, anxiety, depression, ADD, and premenstrual syndrome.

Supplements containing L- Tryptophan are not the subject of regulated manufacturing standards, making them potentially dangerous. It is advised to pay special attention to the supplier of the supplement and also to consult a healthcare professional before using such a product. Impure, contaminated L- Tryptophan based supplements (commercialized by a Japanese company) is believed to be the cause of a life threatening disease occurred in the late 1980’s.Furthermore, not all uses for l-tryptophan have been approved by the FDA.


2) Details on L-Tryptophan Ingredients and Uses

L-Tryptophan includes the following ingredients: L-Tryptophan, Calcium (only the Tablets), Iron (only the Tablets and Capsules), gelatin (capsule), dibasic calcium phosphate, microcrystalline cellulose, silica, and magnesium stearate, stearic acid, modified cellulose gum, and colloidal silicon dioxide.

3) Does L-Tryptophan Work?

Tryptophan is often referred to as L-Tryptophan which is an amino acid. It is stated to work by helping to control the levels of a chemical produced in the brain called serotonin. This product used to be promoted as a means of helping someone to sleep better too, but that use isn’t as commonly advertised as it once was.

Tryptophan also supports immune functions because it is the body’s precursor to the kynurenines that regulate immunity. Scientific studies seem to show that Tryptophan can be converted to niacin in the body. Niacin plays an essential role in supporting circulation, the metabolism of food, a healthy nervous system and the production of hydrochloric acid for the digestive system.

Source Naturals offers this supplement as capsules (500 mg), powder and tablets (500 mg).

It is also important to note that Tryptophan does occur naturally in various foods. When taken from foods, Tryptophan is not associated with any side effects. Unfortunately, we cannot say the same thing about the ingredient included in various supplements. Synthetic Tryptophan was associated with the following side effects: pain in the muscles, fatigue, changes in the appearance of skin, rash on the skin, nerve pain, and loss of hair. More severe side effects and allergic reactions may occur.

Health Benefits

4) L-Tryptophan Health Benefits

  • Reputable and experienced manufacturer
  • Three different alternatives of the product (tablets, powder or capsules).


5) Precautions of L-Tryptophan Use

  • The supplement is not FDA approved
  • Controversial main ingredient
  • No conclusive evidence of clinical trials conducted upon the product
  • No money back guarantee
  • Mixed reviews from consumers.


6) How Much Does L-Tryptophan Cost?

Tryptophan is available in a variety of forms: 500 mg capsule (30 cap, 60 cap, 90 cap or 120 cap per bottle), powder (50 mg or 100 mg) and 500 mg tablets (30 tab, 60 tab or 120 tab per bottle). The price will vary based on quantity or number of tablets/capsules.

Tryptophan cannot be purchased directly from the manufacturer. In exchange, there are numerous local stores, online retailers and international distributors for this product.

How To Take

7) How to Take L-Tryptophan

Source Naturals recommends a dose of 1 tablet three times daily, between meals and preferably with fruit juice. For a restful sleep they recommend 3 capsules before bedtime. In the case of the powder, the recommended dose is of ‚¾ teaspoons. Pregnant or breastfeeding women and women planning to become pregnant, people taking SSRI or MAOI medication are advised to consult a healthcare professional before using this product.


8) Conclusion

L-Tryptophan is a multi targeted amino-acid based, natural formula.It is designed to help induce relaxation and a positive mood and may ensure a restful sleep.

Due to its capacity to convert to niacin, it also supports circulation and health of the nervous system and the production of hydrochloric acid for the digestive system. However the formula’s efficiency is neither clinically proven, nor approved by the FDA. Our readers should be extremely cautious when purchasing a product based on L- Tryptophan. Impure ingredients may lead to severe, potential lethal health conditions.

The manufacturer recommends its use at the advice of the healthcare professional in case of pregnant and nursing women or people under certain kind of medication.

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