5-HTP

5-HTP/Drug Interactions:

  • NoteNote: 5-HTP is a precursor to serotonin; thus, it may interact with agents that modulate levels of serotonin.
  • AnalgesicsAnalgesics: In animals, 5-HTP had analgesic effects, reducing acetic acid induced writhing (116). In patients with fibromyalgia, treatment with 5-HTP resulted in significant improvement in the number of tender points, pain intensity, and the amount of sleep, anxiety, fatigue, and morning stiffness compared to the placebo group (74; 20). In various clinical trials, treatment with 5-HTP resulted in significant improvements in migraines or headaches (82; 117; 36; 99; 24; 21; 118), although this improvement was lacking in other studies (84; 25; 34; 37; 44).
  • Angiotensin-converting enzyme receptor blockers (ARBs)Angiotensin-converting enzyme receptor blockers (ARBs): In animals, losartan decreased pineal serotonin levels (119).
  • AntiarrhythmicsAntiarrhythmics: Palpitations have been reported following oral administration of 5-HTP (57; 37; 42; 51). Conversely, bradycardia has been reported in patients taking both carbidopa (100-300mg daily) and 5-HTP (400-2,000mg daily) (100).
  • AnticonvulsantsAnticonvulsants: According to a review, 5-HTP may inhibit both focal and generalized seizures (61). However, seizures have also been associated with 5-HTP use in humans (60; 61).
  • Antidepressants, monoamine oxidase inhibitors (MAOIs)Antidepressants, monoamine oxidase inhibitors (MAOIs): Theoretically, concurrent use of monoamine oxidase inhibitors and 5-HTP may increase the risk of serotonergic side effects (e.g., serotonin syndrome) (51). The addition of 5-HTP may potentiate the antidepressant effect of MAOIs and decrease time to recovery from depression (120). However, in clinical research, 5-HTP improved depressive symptoms, and appeared as effective as fluoxetine (73; 51; 52). In humans, a combination of L-deprenyl (a monoamine oxidase inhibitor), 5-HTP, and benserazide had greater effects than 5-HTP and benserazide alone (121). In humans, use of lithium carbonate or monoamine oxidase inhibitors augmented the increase in serum cortisol levels in manic or depressed patients taking 5-HTP, whereas tricyclic antidepressants diminished levels (98). In clinical research, concurrent use of MAOI and 5-HTP resulted in a case of mania despite a lack of family history (122).
  • Antidepressant agents, selective serotonin reuptake inhibitors (SSRIs)Antidepressant agents, selective serotonin reuptake inhibitors (SSRIs): In clinical research, 5-HTP improved depressive symptoms, and appeared as effective as fluoxetine (73; 51; 52). However, according to reviewers, a theoretical drug interaction with 5-HTP exists between SSRI antidepressants due to the possibility of causing serotonin syndrome (51). In humans, 5-HTP increased serotonin levels (61). In animal research of mutant mice with a mutation in tryptophan hydroxylase 2 (Tph2), further depletion of tissue 5-HT due to chronic treatment with SSRIs (fluoxetine and paroxetine) was resolved with supplementation of 5-HTP (123).
  • Antidepressant agents, serotonin and norepinephrine reuptake inhibitors (SNRIs)Antidepressant agents, serotonin and norepinephrine reuptake inhibitors (SNRIs): In clinical research, 5-HTP improved depressive symptoms, and appeared as effective as fluoxetine (73; 51; 52). Theoretically, concomitant use of 5-HTP and SNRIs (such as venlafaxine) may increase serotonin levels, resulting in adverse effects, including serotonin syndrome.
  • Antidepressants, tetracyclicsAntidepressants, tetracyclics: In clinical research, 5-HTP improved depressive symptoms, and appeared as effective as fluoxetine (73; 51; 52). Theoretically, concomitant use of 5-HTP and mirtazapine may increase serotonin levels, resulting in adverse effects, including serotonin syndrome.
  • Antidepressants, tricyclic (TCAs)Antidepressants, tricyclic (TCAs): In clinical research, 5-HTP improved depressive symptoms, and appeared as effective as fluoxetine (73; 51; 52). Theoretically, concomitant use may increase serotonin levels, resulting in adverse effects, including serotonin syndrome, although TCAs have been shown lack an effect on the 5-HTP-mediated increase in plasma cortisol and prolactin secretion (124). In humans, use of lithium carbonate or monoamine oxidase inhibitor augmented the increase in serum cortisol in manic or depressed patients taking 5-HTP, whereas tricyclic antidepressants diminished the levels (98).
  • AntihypertensivesAntihypertensives: Anecdotally, 5-HTP may cause blood pressure lowering. Theoretically concurrent use with antihypertensives may increase the risk of hypotension. In vitro, serotonin is a vasoconstrictor; however, in vivo, chronic serotonin and 5-HTP supplementation decreased blood pressure (125). In vitro, the increase in plasma prolactin after 5-HTP administration was blocked by pindolol (58).
  • Anti-inflammatoriesAnti-inflammatories: In vitro, 5-HTP had anti-inflammatory effects, resulting in reduced expression of nitric oxide and interleukin-6 (116). 5-HTP also played a role in lipopolysaccharide-induced inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and extracellular-signal-regulated protein kinase (ERK) activation.
  • AntilipemicsAntilipemics: Patients receiving both carbidopa and 5-HTP had a reduction in total cholesterol (100). The effect of 5-HTP alone is unclear from this research.
  • AntineoplasticsAntineoplastics: In vitro, 5-HTP selectively inhibited PAT1-mediated amino acid uptake (SLC36A1) across the brush-border membrane of the human intestinal (Caco-2) epithelium (126). The authors suggested that this may have anticancer effects.
  • Antiobesity agentsAntiobesity agents: In clinical trials, 5-HTP has promoted weight loss in obese individuals (78; 26; 31; 22). This effect has been potentially attributed to the fact that endogenous hypothalamic serotonin improves within-meal satiation and post-meal satiety processes (127). The use of 5-HTP as part of combination pharmacotherapy, along with phentermine and the peripheral decarboxylase inhibitor carbidopa, has been discussed (17). However, in Drosophila larvae, 5-HTP increased feeding rate, although this was likely due to maturation of the neural circuit at this stage in this species (128).
  • AntiparkinsoniansAntiparkinsonians: 5-HTP has been studied, usually in combination with drugs, for Parkinson's disease (129; 102; 130; 131). In one study, treatment with 5-HTP plus benserazide was reported to reduce shaking and akineto-hypertonic syndrome in patients with Parkinson's disease (102). However, in other research, treatment with 5-HTP plus alpha-methyldopahydrazine exacerbated rigidity and bradykinesia associated with Parkinson's disease (131). The effects of 5-HTP alone are unclear from these studies.
  • Antipsychotic agentsAntipsychotic agents: In animals, 5-HTP enhanced haloperidol-induced bradykinesia and catalepsy (132). The 5-HT(3) and 5-HT(6) receptors played a role in this augmentation. It has been suggested by some authors that 5-HTP may be useful for psychotic symptoms or panic disorder (27; 14); however, studies in people with schizophrenia have shown varying results (133; 134; 135; 27; 23; 47). The effects of 5-HTP with antipsychotic agents are not well understood.
  • Antivirals, ribavirinAntivirals, ribavirin: In clinical research, concurrent use of pegylated interferon-alpha (PEG-IFN alpha) and ribavirin to treat chronic hepatitis C (HCV) decreased plasma 5-HTP levels at one and six months of therapy before returning to baseline three months post-intervention (136).
  • AnxiolyticsAnxiolytics: Theoretically, concomitant use of 5-HTP and anxiolytic drugs (such as buspirone and trazodone) may increase serotonin levels, resulting in adverse effects, including serotonin syndrome.
  • BarbituratesBarbiturates: In animals, diltiazem increased pentobarbital sleep and slow-wave sleep; these effects were potentiated by 5-HTP (137).
  • BenzodiazepinesBenzodiazepines: In animals, diazepam decreased levels of 5-HTP in the brain (138).
  • BenzylpiperazineBenzylpiperazine: According to epidemiological research, taking 5-HTP recovery pills at the same time as "party pills" (benzylpiperazine and trifluoromethylphenylpiperazine) increased the risk of adverse effects (65).
  • CannabinoidsCannabinoids: In animals, marijuana decreased levels of 5-HTP in the brain (138). In animals, 5-HTP inhibited delta(9)-tetrahydrocannabinol (THC)-induced catalepsy (139).
  • CNS depressantsCNS depressants: In humans, 5-HTP has caused drowsiness and somnolence (28; 27; 26; 34; 36; 37; 44). Theoretically, concurrent use with CNS depressants may increase the risk of sedation. In animals, the initial absorption rate of gaboxadol (an experimental sleep aid) was decreased in the presence of 5-HTP (140).
  • Cytochrome P450-metabolized agentsCytochrome P450-metabolized agents: According to secondary sources, 5-HTP may alter the concentrations of CYP450-metabolized agents.
  • Decarboxylase inhibitorsDecarboxylase inhibitors: Carbidopa is used to increase bioavailability of 5-HTP for brain penetration (106). In humans, administration of 5-HTP with decarboxylase inhibitors (carbidopa and benserazide) may increase the plasma concentration and half-life of 5-HTP (54; 55; 56). The combination of 5-HTP and carbidopa may increase the risk of developing scleroderma-like illness in susceptible individuals (104; 103). Carbidopa may alter tryptophan metabolism, which may be associated with development of scleroderma. In patients with Parkinson's disease taking 5-HTP with benserazide, drowsiness, ear buzzing, and palpitations were noted (102). Patients receiving both carbidopa and 5-HTP long-term had a reduction in total cholesterol (100).
  • Dermatologic agentsDermatologic agents: A 70 year-old patient developed sclerodermatous changes with intention myoclonus following 5-HTP 1,400mg daily and carbidopa 150mg daily (103). A 79 year-old patient with Parkinson's disease and chronic depression treated with 5-HTP, carbidopa, and flunitrazepam (dosage unspecified) developed a pseudobullous morphea and scleroderma-like illness. This patient was also taking tryptophan 750mg daily for the previous two years (104). Urticaria has also been noted (25). According to secondary sources, signs of allergy to 5-HTP may include rash or itching. Theoretically 5-HTP may influence the effects of certain dermatologic agents.
  • DiltiazemDiltiazem: In animals, diltiazem increased pentobarbital sleep and slow-wave sleep; these effects were potentiated by 5-HTP (137).
  • Drugs that lower the seizure thresholdDrugs that lower the seizure threshold: According to a review and in human research, extended use of 5-HTP has caused seizures (60; 61). Theoretically, concurrent use of 5-HTP with drugs that lower the seizure threshold may increase the risk of seizures.
  • Gastrointestinal agentsGastrointestinal agents: Gastrointestinal side effects such as nausea, vomiting, abdominal pain, heartburn, diarrhea, flatulence, anorexia, and taste alteration have been reported following the use of 5-HTP and may be dose dependent (25; 26; 20; 27; 28; 29; 30; 22; 31; 32; 33; 34; 35; 36; 37; 21; 38; 39; 40; 19; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52).
  • Growth hormonesGrowth hormones: In men, 5-HTP produced a transient increase in plasma growth hormones (GH) (38). In humans, 5-HTP administration resulted in a rise in GH (141).
  • Hormonal agentsHormonal agents: In humans, 5-HTP increased luteinizing hormone (LH) (53). However, in the absence of gonadotrophin-releasing hormone (GnRH) (e.g., Kallmann's syndrome), 5-HTP did not cause an increase in LH (53). The ability of 5-HTP to modulate visceral hypersensitivity in animals was inhibited by granisetron and accompanied by a decrease in calcitonin gene-related peptide-immunoreactive (CGRP-IR) neurons in the dorsal root ganglion (142). Ovariectomy eliminated 5HTP-induced visceral hypersensitivity; this was restored with estrogen and the combination of estrogen and progesterone. In Japanese quail, 5-HTP inhibited gonadal development (143). In this model, hypo- and hyper-reproductive conditions, as measured by concentrations of plasma testosterone, were experimentally simulated with injections of 5-HTP and L-dihydroxyphenylalanine (L-DOPA) (144).
  • Lithium carbonateLithium carbonate: According to secondary sources, lithium may alter serotonin synthesis. In animals, lithium enhanced the components of the serotonin syndrome produced by 8-hydroxy-2-(di-propylamino)tetralin (8-OH-DPAT) (145).
  • MethamphetamineMethamphetamine: In animals, increases in serotonin levels with 5-HTP reportedly lacked an effect on methamphetamine-induced neurotoxicity to dopamine nerve endings (146).
  • MetoclopramideMetoclopramide: In humans, 5-HTP induced release of corticotrophin-releasing-hormone (CRH) (147); this effect was potently synergized by metoclopramide.
  • PEG-IFN alphaPEG-IFN alpha: In clinical research, concurrent use of pegylated interferon-alpha (PEG-IFN alpha) and ribavirin to treat chronic hepatitis C (HCV) decreased plasma 5-HTP levels at one and six months of therapy before returning to baseline three months post-intervention (136).
  • SedativesSedatives: In humans, 5-HTP has caused drowsiness and somnolence (28; 27; 26; 34; 36; 37; 44). Theoretically, concurrent use with CNS depressants may increase the risk of sedation. In animals, the initial absorption rate of gaboxadol (an experimental sleep aid) was decreased in the presence of 5-HTP (140).
  • Serotonin receptor antagonistsSerotonin receptor antagonists: Theoretically, serotonin receptor antagonists, such as methysergide, nefazodone, and cyproheptadine, may diminish efficacy of 5-HTP. In vitro, the 5-HTP-induced increase in plasma cortisol was blocked by administration of ritanserin, a 5-HT2/5-HT1C antagonist (58).
  • Sulfa drugsSulfa drugs: In vitro, sulfa drugs interfered with tetrahydrobiopterin biosynthesis, a cofactor in the production of 5-HTP, through inhibition of sepiapterin reductase (148).
  • Tetrahydrobiopterin (BH4)Tetrahydrobiopterin (BH4): In clinical research, BH4 is administered to individuals with 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency; however, severe side effects are possible with co-administration of 5-HTP and L-DOPA and caution is warranted (149).
  • Thyroid hormonesThyroid hormones: In men, 5-HTP produced an increase in thyroid-stimulating hormone (TSH) (38).
  • Triptorlin depotTriptorlin depot: In clinical research, treatment with triptorelin depot in individuals with central precocious puberty (CPP) resulted in increased urine levels of 5-HTP (150).

    • 5-HTP/Herb/Supplement Interactions:

  • Alpinia zerumbetAlpinia zerumbet: In animals, intraperitoneal injection of 5-HTP decreased jumping frequencies associated with administration of the essential oil from the leaves of Alpinia zerumbet (Alpinia speciosa K.Schum.) (151).
  • Analgesic herbs and supplementsAnalgesic herbs and supplements: In animals, 5-HTP had analgesic effects, reducing acetic acid induced writhing (116). In patients with fibromyalgia, treatment with 5-HTP resulted in significant improvement in the number of tender points, pain intensity, and the amount of sleep, anxiety, fatigue, and morning stiffness compared to the placebo group (74; 20). In various clinical trials, treatment with 5-HTP resulted in significant improvements in migraines or headaches (82; 117; 36; 99; 24; 21; 118), although this improvement was lacking in other studies (84; 25; 34; 37; 44).
  • AntiarrhythmicsAntiarrhythmics: Palpitations have been reported following oral administration (57; 37; 42; 51). Conversely, bradycardia has been reported in patients taking both carbidopa (100-300mg daily) and 5-HTP (400-2,000mg daily) (100).
  • AnticonvulsantsAnticonvulsants: According to a review, 5-HTP may inhibit both focal and generalized seizures (61). However, seizures have also been associated with 5-HTP use in humans (60; 61).
  • Antidepressants, monoamine oxidase inhibitors (MAOIs)Antidepressants, monoamine oxidase inhibitors (MAOIs): In clinical research, 5-HTP improved depressive symptoms (73; 51; 52). Concomitant use with herbs or supplements with MAOI activity may increase serotonin levels, resulting in adverse effects, including serotonin syndrome (theoretical). In clinical research, concurrent use of MAOI and 5-HTP resulted in a case of mania despite a lack of family history (122).
  • Antidepressants, selective serotonin reuptake inhibitors (SSRIs)Antidepressants, selective serotonin reuptake inhibitors (SSRIs): In clinical research, 5-HTP improved depressive symptoms (73; 51; 52). In humans, 5-HTP increased serotonin levels (61); theoretically, when combined with an SSRI, the serotonin level may be increased sufficiently to produce serotonin syndrome.
  • Anti-inflammatoriesAnti-inflammatories: In vitro, 5-HTP had anti-inflammatory effects, resulting in reduced expression of nitric oxide and interleukin-6 (116). 5-HTP also played a role in lipopolysaccharide-induced inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and extracellular-signal-regulated protein kinase (ERK) activation.
  • AntilipemicsAntilipemics: Patients receiving both carbidopa and 5-HTP had a reduction in total cholesterol (100).
  • AntineoplasticsAntineoplastics: In vitro, 5-HTP selectively inhibited PAT1-mediated amino acid uptake (SLC36A1) across the brush-border membrane of the human intestinal (Caco-2) epithelium (126). The authors suggested that this may have anticancer effects.
  • Antiobesity herbs and supplementsAntiobesity herbs and supplements: In clinical trials, 5-HTP has promoted weight loss in obese individuals (78; 26; 31; 22). This effect has been potentially attributed to the fact that endogenous hypothalamic serotonin improves within-meal satiation and post-meal satiety processes (127). However, in Drosophila larvae, 5-HTP increased feeding rate, although this was likely due to maturation of the neural circuit at this stage in this species (128).
  • AntioxidantsAntioxidants: In in vitro research, 5-HTP had antioxidant effects on cell membranes (152; 153). 5-HTP was able to attenuate the cell membrane rigidity, as well as malondialdehyde and 4-hydroxyalkenal levels in FeCl3-treated membranes. In fibroblast cells in vitro, 5-HTP prevented tert-butylhydroperoxide (t-BHP)-induced oxidative damage (154).
  • AntiparkinsoniansAntiparkinsonians: 5-HTP has been studied, usually in combination with drugs, for Parkinson's disease (129; 102; 130; 131). In one study, treatment with 5-HTP plus benserazide was reported to reduce shaking and akineto-hypertonic syndrome in patients with Parkinson's disease (102). However, in other research, treatment with 5-HTP plus alpha-methyldopahydrazine exacerbated rigidity and bradykinesia associated with Parkinson's disease (131). The effects of 5-HTP alone are unclear from these studies.
  • AntipsychoticsAntipsychotics: In animals, 5-HTP enhanced haloperidol-induced bradykinesia and catalepsy (132). The 5-HT(3) and 5-HT(6) receptors played a role in this augmentation. It has been suggested by some authors that 5-HTP may be useful for psychotic symptoms or panic disorder (27; 14); however, studies in people with schizophrenia have shown different results (133; 134; 135; 27; 23; 47). The effects with antipsychotic agents are not well understood.
  • AnxiolyticsAnxiolytics: Theoretically, concomitant use of 5-HTP and anxiolytic agents may increase serotonin levels, resulting in adverse effects, including serotonin syndrome.
  • CannabinoidsCannabinoids: In animals, marijuana decreased levels of 5-HTP in the brain (138). In animals, 5-HTP inhibited delta(9)-tetrahydrocannabinol (THC)-induced catalepsy (139).
  • ChromiumChromium: Theoretically, chromium may increase the side effects associated with 5-HTP.
  • Cytochrome P450-metabolized herbs and supplementsCytochrome P450-metabolized herbs and supplements: According to secondary sources, 5-HTP may alter the concentrations of CYP450-metabolized herbs and supplements.
  • Gastrointestinal herbs and supplementsGastrointestinal herbs and supplements: Gastrointestinal side effects such as nausea, vomiting, abdominal pain, heartburn, diarrhea, flatulence, anorexia, and taste alteration have been reported following the use of 5-HTP and may be dose dependent (25; 26; 20; 27; 28; 29; 30; 22; 31; 32; 33; 34; 35; 36; 37; 21; 38; 39; 40; 19; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52).
  • Griffonia simplicifolia extractGriffonia simplicifolia extract: In a clinical trial, supplementation with Griffonia simplicifolia extract resulted in 5-HTP absorption as indicated by an increase in 24 hour urinary 5-hydroxyindoleacetic acid (5-HIAA) levels (155).
  • Herbs that lower seizure thresholdHerbs that lower seizure threshold: According to a review and in human research, extended use of 5-HTP has caused seizures in humans (60; 61). Theoretically, concurrent use of 5-HTP with drugs that lower the seizure threshold may increase the risk of seizures.
  • Hormonal herbs and supplementsHormonal herbs and supplements: In humans, 5-HTP increased luteinizing hormone (LH) (53). However, in the absence of gonadotrophin-releasing hormone (GnRH) (e.g., Kallmann's syndrome), 5-HTP did not cause an increase in LH (53). The ability of 5-HTP to modulate visceral hypersensitivity in animals was inhibited by granisetron and accompanied by a decrease in calcitonin gene-related peptide-immunoreactive (CGRP-IR) neurons in the dorsal root ganglion (142). Ovariectomy eliminated 5-HTP-induced visceral hypersensitivity; this was restored with estrogen and the combination of estrogen and progesterone. In Japanese quail, 5-HTP inhibited gonadal development (143). In this model, hypo- and hyper-reproductive conditions, as measured by concentrations of plasma testosterone, were experimentally simulated with injections of 5-HTP and L-dihydroxyphenylalanine (L-DOPA) (144).
  • HypotensivesHypotensives: Anecdotally, 5-HTP may cause blood pressure lowering. Theoretically concurrent use with antihypertensives may increase the risk of hypotension. In vitro, the increase in plasma prolactin after 5-HTP administration was blocked by pindolol (58).
  • Jujubosides from Ziziphus jujuba Mill. var. spinosa (bunge) Hu ex H.F.ChowJujubosides from Ziziphus jujuba Mill. var. spinosa (bunge) Hu ex H.F.Chow: In animals, 5-HTP potentiated the jujuboside-augmented hypnotic effect of pentobarbital (156).
  • L-tyrosineL-tyrosine: The catecholamine precursor L-tyrosine may potentiate the antidepressant effect of 5-HTP in humans (157).
  • MagnesiumMagnesium: According to secondary sources, concomitant use of magnesium and 5-HTP may increase serotonin levels, resulting in adverse effects, including serotonin syndrome.
  • MelatoninMelatonin: In theory, melatonin may increase the effects or side effects associated with 5-HTP. According to secondary sources, 5-HTP, theanine, and melatonin taken together aid in sleep.
  • NiacinNiacin: According to secondary sources, concomitant use of niacin and 5-HTP may increase serotonin levels, resulting in adverse effects, including serotonin syndrome.
  • SAMeSAMe: Theoretically SAMe and 5-HTP may have additive effects when used in combination.
  • SedativesSedatives: In humans, 5-HTP has caused drowsiness and somnolence (28; 27; 26; 34; 36; 37; 44). Theoretically, concurrent use with CNS depressants may increase the risk of sedation. In animals, the initial absorption rate of an experimental sleep aid was decreased in the presence of 5-HTP (140).
  • Serotonin receptor antagonistsSerotonin receptor antagonists: Theoretically, serotonin receptor antagonists may diminish the efficacy of 5-HTP. In clinical research, 5-HTP elevated extracellular serotonin levels (61; 127).
  • SodiumSodium: An intravenous derivative of 5-HTP called gamma-L-glutamyl 5-HTP administered over one hour resulted in sodium retention (109); it is unknown if this effect was the result of the formulation, the route of administration, or the rate of infusion.
  • SpinosinSpinosin: In animals, 5-HTP augmented the augmentation of pentobarbital-induced sleep induced by spinosin (a major constituent of Zizhiphi spinozae seeds) (158).
  • St. John's wortSt. John's wort: Theoretically, concomitant use may increase serotonin levels, resulting in adverse effects, including serotonin syndrome.
  • TheanineTheanine: According to secondary sources, 5-HTP, theanine, and melatonin taken together aid in sleep.
  • Thyroid herbs and supplementsThyroid herbs and supplements: 5-HTP produced an increase in thyroid-stimulating hormone (TSH) (38).
  • TryptophanTryptophan: When tryptophan and 5-HTP are used in combination, additive effects may result (anecdotal).
  • Vitamin B6Vitamin B6: Pyridoxal phosphate (vitamin B6) is known to be necessary for enzymatic conversion of 5-HTP to serotonin. Theoretically, concomitant use may increase serotonin levels, resulting in adverse effects, including serotonin syndrome.

    • 5-HTP/Food Interactions:

  • ProteinProtein: The effect of protein ingestion has been examined on 5-HTP levels in the brain (159). Further details are lacking at this time.
  • Sodium-containing foodsSodium-containing foods: An intravenous derivative of 5-HTP called gamma-L-glutamyl 5-HTP administered over one hour resulted in sodium retention (109); it is unknown if this effect was the result of the formulation, the route of administration, or the rate of infusion.
  • Tryptophan-containing foodsTryptophan-containing foods: The ingestion of foodstuffs containing tryptophan may theoretically result in additive effects when taken with 5-HTP; however, clinical data are lacking.
  • Vitamin B6-containing foodsVitamin B6-containing foods: Pyridoxal phosphate (vitamin B6) is known to be necessary for enzymatic conversion of 5-HTP to serotonin. Theoretically, concomitant use may increase serotonin levels, resulting in adverse effects, including serotonin syndrome.

    • 5-HTP/Lab Interactions:

  • 5-Hydroxyindoleacetic acid (5-HIAA)5-Hydroxyindoleacetic acid (5-HIAA): In humans, 5-HTP increased excretion of 5-HIAA (160), commonly measured for biochemical detection of carcinoid tumors (161). It was suggested that increased 5-HIAA levels with normal CgA levels may suggest 5-HTP ingestion, as opposed to a carcinoid tumor. In a clinical trial, supplementation with Griffonia simplicifolia extract resulted in 5-HTP absorption as indicated by an increase in 24 hour urinary 5-hydroxyindoleacetic acid (5-HIAA) levels (155).
  • Adrenocorticotropic hormone (ACTH)Adrenocorticotropic hormone (ACTH): One study showed that 5-HTP resulted in a rise in ACTH in six out of eight subjects tested (141). Increased ACTH has been shown in other human studies following administration of the 5-HTP function test (5-HTP, carbidopa, and granisetron) (162).
  • Blood pressureBlood pressure: Anecdotally, 5-HTP may lower blood pressure. Theoretically, concurrent use with antihypertensives may increase the risk of hypotension. In vitro, the increase in plasma prolactin seen after 5-HTP administrations has been blocked by pindolol (58).
  • Body temperatureBody temperature: In animals, 5-HTP altered body temperature (163). Further details are not available.
  • Corticotrophin-releasing hormoneCorticotrophin-releasing hormone: In humans, 5-HTP induced release of corticotrophin-releasing hormone (CRH) (147).
  • Cortisol (blood and salivary)Cortisol (blood and salivary): Several studies have shown that 5-HTP induces an increase in plasma cortisol (141; 38; 164; 58; 165; 47; 106; 64; 98; 162). Increased salivary cortisol was noted in patients with panic disorder (135).
  • Dehydroepiandrosterone (DHEA-S)Dehydroepiandrosterone (DHEA-S): In autistic patients, 5-HTP increased plasma DHEA-S more than in control subjects (166).
  • Glutamate/glutamineGlutamate/glutamine: In humans, administration of the 5-HTP function test (5-HTP, carbidopa, and granisetron) resulted in reduced glutamate/glutamine at 60 minutes (162).
  • Growth hormone (GH)Growth hormone (GH): In men, 5-HTP produced a transient increase in plasma GH (38). In humans, 5-HTP administration resulted in a rise in GH (141).
  • Heart rateHeart rate: Bradycardia has been reported in patients taking both carbidopa and 5-HTP (100).
  • Luteinizing hormone (LH)Luteinizing hormone (LH): In humans, 5-HTP increased LH (53). However, in the absence of GnRH (e.g., Kallmann's syndrome), 5-HTP did not cause an increase in LH.
  • Lipid profileLipid profile: Patients receiving both carbidopa and 5-HTP had a reduction in total cholesterol (100).
  • PEG-IFN alphaPEG-IFN alpha: In clinical research, concurrent use of pegylated interferon-alpha (PEG-IFN alpha) and ribavirin to treat chronic hepatitis C (HCV) decreased plasma 5-HTP levels at one and six months of therapy before returning to baseline three months post-intervention (136).
  • Prolactin (blood)Prolactin (blood): There have been inconsistent effects (increase, decrease) on plasma prolactin levels with use of 5-HTP (38; 113; 58; 35).
  • SerotoninSerotonin: In humans, 5-HTP resulted in increased urinary serotonin excretion (167). In animals, 5-HTP increased serotonin in all five brain areas (168). In animal research investigating the presence of serotonin in mammalian cardiomyocytes, the addition of 5-HTP to adult mice resulted in increased 5-HT levels (169).
  • Sodium (blood)Sodium (blood): In humans, an intravenous derivative of 5-HTP (gamma-L-glutamyl 5-HTP) resulted in sodium retention (109).
  • Thyroid-stimulating hormone (TSH)Thyroid-stimulating hormone (TSH): In men, 5-HTP produced an increase in thyroid-stimulating hormone (TSH) (38).
  • Triptorlin depotTriptorlin depot: In clinical research, treatment with triptorelin depot in individuals with central precocious puberty (CPP) resulted in increased urine levels of 5-HTP (150).