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What is 5-HTP?
5-HTP (5-hydroxytryptophan) is a naturally-occurring metabolite of the
essential amino acid tryptophan. 5-HTP for use in dietary supplements is
derived from the seeds of the Griffonia simplicifolia plant.
Metabolism and absorption of 5-HTP
5-HTP (5-hydroxytryptophan) is formed by the addition of a hydroxyl group (-OH)
to the 5 carbon of the indole ring of tryptophan. Conversion of tryptophan to
5-hydroxytryptophan is catalyzed by the enzyme tryptophan hydroxylase.1 5-HTP
functions as the precursor for serotonin, and is converted to serotonin in a
pyridoxal phosphate (vitamin B6) dependent reaction catalyzed by the enzyme
L-amino acid decarboxylase.2
Synthesis of serotonin in the brain requires an adequate supply of either
tryptophan or 5-HTP as precursors. The supply of tryptophan available for
conversion to 5-HTP depends on a number of factors, including nutritional
status and competition between tryptophan and other amino acids for transport
across the blood brain barrier.
Disturbances in the serotonin metabolic pathway may disrupt central nervous
system functions which utilize serotonin as a neurotransmitter.2 Administration
of 5-HTP bypasses the conversion of tryptophan to 5-HTP. 5-HTP readily crosses
the blood brain barrier and becomes available for serotonin synthesis.
Serotonergic neurons (nerve cells stimulated by serotonin) regulate sleep,
appetite, nociception (the perception of pain), and aggressive behavior.2
Serotonin is metabolized to 5-HIAA (5-hydroxyindolacetic acid) which is its
primary breakdown product.3 The concentration of 5-HIAA in cerebrospinal fluid
is used as an indicator of serotonin turnover in the CNS serotonin level.
Psychiatric patients have been found to have low levels of 5-HIAA in the CNS
fluid, suggesting serotonin deficiency.3
5-HTP is readily absorbed by the mucosal cells of the gastrointestinal tract.
The delivery of 5-HTP into general circulation is enhanced by the concomitant
administration of an L-amino acid decarboxylase inhibitor such as carbidopa,
which reduces the conversion of 5-HTP to serotonin in the gut and in liver. In
one study using five subjects, systemic absorption of 5-HTP in combination with
carbidopa averaged 69.2 percent.4 Another absorption study found that carbidopa
enhanced the increase in serum 5-HTP concentration 5 to 15 fold.5 In this
study, a single dose of 5-HTP increased the plasma level of 5-HTP only
slightly, whereas 5-HIAA increased 9-20 fold. This suggests that the gut mucosa
has a storage capacity for 5-HTP, and that plasma increases occur after maximum
capacity is reached.5
Observed Effects of 5-HTP Administration
Improves Well-Being in Depressed Persons
Serotonin in the central nervous system is recognized as a causative factor in
some depressed persons.6,7 A comprehensive review of seven open and seven
controlled clinical studies found that oral consumption of 5-HTP improved
mental and emotional status in 60 to 70 percent of depressed people. The
results varied from "modest" to "marked."8 Dosages ranged
from 50 to 300 mg daily.
The accumulated evidence is inconclusive as to whether 5-HTP is more effective
combined with decarboxylase inhibitors than when taken alone. Many of the early
trials used the combination, and this has been a frequently used therapeutic
strategy for reducing conversion of 5-HTP to serotonin outside the CNS. It is
generally accepted that a large portion of absorbed 5-HTP is metabolized to
serotonin in peripheral tissues before it can enter the brain.8
Peripheral conversion of 5-HTP to serotonin would theoretically limit the
usefulness of oral 5-HTP for improving CNS functions and mental health.
However, trials in which 5-HTP was given alone do show benefits. A small open
trial in which 25 people were given 5-HTP either alone or with a decarboxylase
inhibitor found no difference in effectiveness.9 Thirteen of the patients had
"very good" or "good" improvement, 8 had
"moderate," and in 4 out of the twenty-five the results were judged
to be "poor."
A more recent randomized double-blind study compared the efficacy of oral 5-HTP
(100 mg T.I.D., without a decarboxylase inhibitor) to that of fluvoxamine, a
selective serotonin reuptake inhibitor.10 (SSRIs block the reabsorption of
serotonin by postsynaptic receptors, thus increasing the available supply of
serotonin in the synaptic cleft.) The two were found to be equally effective,
and 5-HTP was better tolerated. It should be noted that 5-HTP was given in the
form of enteric-coated pH-sensitive capsules which dissolve in the small
intestine, thus preventing conversion of 5-HTP to serotonin in the stomach.
In contrast to MAO inhibitors and SSRIs, medications which act by blocking
normal physiologic functions, 5-HTP supports normal function in its role as a
serotonin precursor. Correcting serotonin deficiency has been called a
"functional-dimensional approach" in the treatment of depression.10
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Improves Sleep Quality
Studies have shown that 5-HTP influences the quality of sleep by increasing REM
(rapid eye movement) sleep. Administration of 5-HTP in the evening prior to
bedtime has been shown to increase the duration of REM sleep and decrease the
amount of non-REM sleep.11,12
Helps Prevent Migraine Headaches
Serotonin is known to play an important role in the pathophysiology of migraine
headaches.13 Serotonin regulates a key pain control system which is activated
during a migraine attack.14 In a placebo-controlled, double-blind cross-over
study 31 people with migraine took 400 mg of 5-HTP per day. By the second
month, 5-HTP reduced the frequency and severity of attacks by more than 50
percent in 52 percent of the subjects, although the results were not
statistically significant.13 In a larger study using 124 migraine sufferers,
5-HTP for migraine prevention was compared to methysergide.14 Seventy-one
percent of the subjects taking 5-HTP (600 mg per day) experienced significant
reduction of intensity and duration of attacks, compared to seventy-five
percent of those taking the drug. Side effects were less frequent in the 5-HTP
Improves Clinical Parameters in Fibromyalgia
Disturbances in serotonin-controlled nervous system function are believed to be
a factor in fibromyalgia.15 In a 90 day open trial, 50 people with primary
fibromyalgia received 100 mg of 5-HTP three times daily.16 Nearly 50 percent
showed "good" or "fair improvements in clinical parameters such
as the number of tender points, anxiety, fatigue and sleep quality. A placebo
controlled, double-blind study on 50 patients produced similar significant
5-HTP A Free-radical Scavenger
The OH group which is added to tryptophan in the formation of 5-HTP gives 5-HTP
antioxidant properties.18 (Compounds such as vitamin E and flavonoids derive
their free-radical quenching ability from OH groups, which donate electrons to
oxidants.) 5-HTP quenches a variety of free-radicals. This is in contrast to
tryptophan, which is sensitive to oxidation.
Adverse effects of 5-HTP
Oral administration of 5-HTP in clinical studies has resulted in
gastrointestinal disturbances such as nausea, vomiting and diarrhea. According
to a review by Byerley, et. al. these effects are tolerated by most patients
and tend to lessen over time.8 Side effects are more marked with higher doses,
and may be reduced by the use of enteric-coated, pH sensitive capsules or
1. Pike, R.L., Brown, M.L. Nutrition: An Integrated Approach. NY: Macmillan
Pub. Co.; 1986:626-28.
2. Peters, J.C. Tryptophan nutrition and metabolism: An overview. Advances in
Experimental Medicine and Biology 1991;294:345-349.
3. van Pragg, H.M. Central monoamine metabolism in depressions. I. Serotonin and
related compounds. Comprehensive Psychiatry 1980;21(1):30-43.
4. Magnussen, I., Neilsen-Kudsk, F. Bioavailability and related pharmacokinetics
in man of orally administered L-5-hydroxytryptophan in steady state. Acta
pharmacol. et toxicol. 1980;46:257-62.
5. Magnussen, I., Jensen, T.S., Rand, J.H., Van Woert, M.H. Plasma accumulation
and metabolism of orally administered single dose L-5-hydroxytryptophan in man.
Acta pharmacol. et toxicol. 1981;49:184-89.
6. van Pragg, H.M. Korf, J. 5-hydroxytryptophan as an antidepressant. Journal of
Nervous and Mental Disease 1974;158(5):331-37.
7. van Pragg, H.M. Management of depression with serotonin precursors.
Biological Psychiatry 1981;16(3):291-310.
8. Byerley, W.F. et. al. 5-Hydroxytryptophan: A review of its antidepressant
efficacy and adverse effects. Journal of Clinical Psychopharmacology
9. Zmilacher, K. Battegay, R., Gastpar, M. L-5-hydroxytryptophan alone and in
combination with a peripheral decarboxylase inhibitor in the treatment of
depression. Neuropsychobiology 1988;20:28-35.
10. Pldinger, W., Calanchini, B., Schwarz, W. A functional-dimensional
approach to depression: Serotonin deficiency as a target syndrome in a
comparison of 5-hydroxytryptophan and fluvoxamine. Psychopathology
11. Zarcone, V.P. Hoddes, E., Smythe, H. Oral 5-hydroxytryptophan effects on
sleep. in Serotonin and Behavior, edited by Barchas, J., Usidin, E., NY:
Academic Press; 1973:499-505.
12. Wyatt, R.J., et. al. Effects of 5-hydroxytryptophan on the sleep of normal
human subjects. Electroencephalography and Clinical Neurophysiology
13. De Benedittis, G., Massei, R. 5-HT precursors in migraine prophylaxis: A
double-blind cross-over study with L-5-hydroxytryptophan versus placebo. The
Clinical Journal of Pain 1986;2:123-129.
14. Titus, F., Dvalos, A., Alom, J., Codina, A. 5-hydroxytryptophan versus
methysergide in the prophylaxis of migraine. Eur. Neurol. 1986;25:327-29.
15. Nicolodi, M., Sicuteri, F. Fibromyalgia and migraine, two faces of the same
mechanism. Recent Advances in Tryptophan Research, Vol. 398, edited by
Filippini, G.A., et. al., NY: Plenum Press; 1996:373-79.
16. Puttini, P.S., Caruso, I. Primary fibromyalgia syndrome and
5-hydroxy-L-tryptophan: a 90 day open study. The Journal of International
Medical Research 1992;20:182-89.
17. Caruso, I., Puttini, P.S., Cazzola, M., Azzolini, V. Double-blind study of
5-hydroxytryptophan versus placebo in the treatment of primary fibromyalgia
syndrome. The Journal of International Medical Research 1990;18:201-09.
18. Simic, M.G. Al-Sheikhly, M. Jovanovic, S.V. Inhibition of free radical
processes by antioxidantsÐtryptophan and 5-hydroxytrytophan. Bibl Nutra