L-Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. This means that it cannot be synthesized by the organism and therefore must be part of its diet. Amino acids, including tryptophan, act as building blocks in protein biosynthesis. In addition, tryptophan functions as a biochemical precursor for the following compounds:

  • Serotonin (a neurotransmitter), synthesized via tryptophan hydroxylase. Serotonin, in turn, can be converted to melatonin (a neurohormone), via N-acetyltransferase and 5-hydroxyindole-O-methyltransferase activities.
  • Niacin is synthesized from tryptophan via kynurenine and quinolinic acids as key biosynthetic intermediates.
  • Auxin (a phytohormone) when sieve tube elements undergo apoptosis tryptophan is converted to auxins.

Clinical research has shown L-Tryptophan to be an effective sleep aid. Furthermore tryptophan has shown some effectiveness for treatment of a variety of other conditions typically associated with low serotonin levels in the brain such as premenstrual dysphoric disorder and seasonal affective disorder. In particular, tryptophan has shown considerable promise as an antidepressant alone and as an “augmenter” of antidepressant drugs.

Tryptophan the anti-depressive/anti-agitate/anti-anxiety protocol

Published research (S.N. Young and H.M. Praag) strongly suggests that L-Tryptophan is very beneficial to “Anxious-Agitated” depressive types. Young and Praag have revealed that at low levels of psychobiologic arousal, there is adequate neuronal serotonin to support the correlative low-level serotonin nerve activity, even when nerve serotonin levels are low. At higher levels of arousal, however, the more rapid turnover of serotonin in the synaptic gap will require higher levels of serotonin production to adequately maintain the greater activity of serotonin circuits. On other words, L-Tryptophan provides the anxious agitated depressive with needed relaxing counterbalance, restoring a sense of well being and behavioral self-control.

Why L-Tryptophan may be even more beneficial than 5-HTP for some users.

Supplemental L-Tryptophan can be a major advantage over 5HTP for some people. Here’s why. We all have many, many serotonin receptor sites lining our intestinal tract. These nerves contain the carboxylase enzyme that converts 5HTP to serotonin, but not the hydroxylase enzyme that coverts tryptophan to 5HTP. Thus, when 5HTP is swallowed, large amounts of 5HTP may be picked up by these intestinal serotonergic neurons and quickly converted to serotonin, leading to hyperactivity of these nerves. This in turn may lead to nausea, vomiting, cramping, constipation and/ or diarrhea, and indeed, the research published on 5HTP since the 1970’s has consistently shown various forms of intestinal discomfort to be the main side effect of 5HTP use. Yet, because these intestinal neurons cannot convert tryptophan to 5HTP, tryptophan does not cause intestinal distress.


Studies have used high L-tryptophan doses for insomnia treatment (1000 mg to 2500 mg daily) and premenstrual syndrome treatment (6000 mg per day), while lower doses (500 mg daily, in combination with natural and pharmaceutical antidepressants) were used for depression studies. A safe maximum dose (known as the “tolerable upper intake level” or UL) for L-tryptophan has not been established.


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