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Dietary supplement

L-Tryptophan Ingredients & Drug Interactions

by Klaire Labs

L-Tryptophan label
See full label image
Capsule Category: Amino Acid/protein
Most serious interaction: Major
Clinical methodology reviewed by · Updated Sep 16, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking L-Tryptophan against your medications. The heart of this page is the interaction checker and the full interaction report — how this product’s ingredients may interact with prescription and over-the-counter medicines you may be taking.

Around that, we add a pharmacist’s high-level view of the product as a whole — what’s inside, the evidence for its stated use, how transparent the label is, and what safety data exists — so you can see the full picture in one place. It’s educational information from our licensed clinical databases and the clinical staff at HelloPharmacist — not medical advice — and we don’t sell or endorse products. Our editorial policy

The interaction bottom line Most serious interaction: Major

L-Tryptophan is a dietary supplement by Klaire Labs with 1 active ingredient. Its ingredients are commonly taken for sleep problems, low mood and depression, anxiety.Based on those ingredients, 394 medications have a known interaction with it, the most serious rated major. The ingredients most likely to interact are L-Tryptophan. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

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Check Your Meds Against L-Tryptophan by Klaire Labs

Ask about any prescription or over-the-counter medication and we check it for interactions with L-Tryptophan by Klaire Labs — and tell you which ingredient is responsible.

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HelloPharmacist Scorecard of L-Tryptophan by Klaire Labs

Our pharmacy team’s full take, with four database checks built into the cards below — a summary of what is known, not a grade of the product itself.

From our pharmacy team — supplement deep dive

Generated from HelloPharmacist’s pharmacist-curated databases and editorial rules · Last generated Jul 11, 2026

What’s inside

Full disclosure
Ingredient Transparency · database check
Full

Every active ingredient lists its own amount on the label.

Why this rating?
  • The label discloses an exact amount for 1 of its 1 active ingredient.
  • No proprietary blends here — you can verify the dose of every single component.

This product contains one active ingredient: L-tryptophan, an amino acid your body uses to make serotonin and other neurotransmitters. The capsule also holds inactive ingredients including hydroxypropyl methylcellulose (the capsule material), microcrystalline cellulose (a filler), ascorbyl palmitate (a preservative), and water.

Does it work?

Not established
Evidence for Intended Use · database check
By FDA rules, dietary supplements can’t claim to treat, cure, or prevent disease — so labels speak in careful marketing language. We discern each product’s intended use from its name, label claims, and label statements, then grade the clinical evidence for that use. How these ratings are computed
Not established

The graded evidence we hold for these ingredients covers different conditions than the ones this product is marketed for, so there's no established rating for its stated use — see L-tryptophan's own graded uses on its monograph.

Why this rating?
  • The label markets this product for: Sleep support.
  • We looked for evidence on: Anxiety, Depression, Premenstrual syndrome (PMS), Premenstrual dysphoric disorder (PMDD), Seasonal affective disorder (SAD), Sleep quality — and 2 related terms.
  • The closest evidence on file: L-tryptophan is rated "Possibly Ineffective" for Depression (Natural Medicines).
  • Also on file: L-tryptophan is rated "Insufficient Reliable Evidence To Rate" for Anxiety, Premenstrual dysphoric disorder (PMDD), Premenstrual syndrome (PMS), Seasonal affective disorder (SAD).

The evidence for L-tryptophan's effectiveness is mixed and often limited. For depression, current data rates it as possibly ineffective.

For anxiety, athletic performance, teeth grinding (bruxism), and premenstrual dysphoric disorder, we don't have enough reliable evidence to know whether it works — the data we hold simply isn't established for those uses.

The evidence, ingredient by ingredient L-tryptophan

How safe is it?

Well-documented data
Safety Information · database check
Well characterized

Adverse-effect, pregnancy, and general safety data are on file for most of these ingredients.

Why this rating?
  • We hold adverse-effect (side-effect) data for 1 of the 1 matched ingredient.
  • Pregnancy & breastfeeding safety ratings cover 1 of 1.
  • General safety write-ups exist for 1 of 1.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

L-tryptophan is generally well tolerated, but common side effects include drowsiness, nausea, diarrhea, headache, heartburn, stomach pain, dry mouth, flatulence, lightheadedness, belching, visual blurring, and vomiting. There's one serious safety note to know: in 1989, more than 1,500 cases of a rare neurological disorder called eosinophilia-myalgia syndrome (EMS) were linked to contaminated L-tryptophan from a single Japanese manufacturer.

About 95% of those cases traced back to that source, and the FDA restricted over-the-counter L-tryptophan imports afterward. Modern products from reputable makers are generally considered safe, but the history warrants caution.

Don't use this product during pregnancy — there isn't enough safety data. The same applies to breastfeeding; safety is not established, so it's best avoided while nursing.

If you're pregnant or breastfeeding, talk to your doctor or pharmacist before considering it.

Side effects, ingredient by ingredient L-tryptophan

Meds to double-check

Major interaction found
Known Interaction Concern · database check
Major identified

At least one ingredient has a documented Major-severity interaction. Check your medications for a personalized result.

Why this rating?
  • 1 of the 1 matched ingredient can interact with medications — L-tryptophan.
  • The most serious interaction on file is rated Major.
  • For scale: 394 individual medications appear in the full list. A big number alone doesn't make a product dangerous — what matters is whether YOUR medication is on it, so run yours through the interaction checker on this page.

Before taking this L-tryptophan, double-check any CNS depressants you're on (such as sleep aids, anxiety drugs, or opioids) — combining them could make you dangerously drowsy. Also review any serotonergic medications like antidepressants or migraine treatments, since L-tryptophan may amplify their effects and raise the risk of serotonin syndrome.

Use the search tool on this page to check your exact prescriptions.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFully disclosed formula with no established evidence rating for its marketed use. Major medication interactions have been identified, and safety information is well characterized.

L-Tryptophan may appeal to people looking for a natural way to support mood or sleep, but the effectiveness evidence is weak for most uses. It's not for you if you take sedating medications, antidepressants, or other serotonergic drugs — the interaction risks are real.

Check your medications with the tool on this page, and ask your pharmacist whether it's a fit for your situation.

Educational only — not medical advice; always confirm with your pharmacist. Our editorial policy · How we use AI

Assessment coverage: 1 of 1 active ingredient matched to our full ingredient reviews (monographs). Based on the product label dated Dec 21, 2024.

This Scorecard evaluates available label information, ingredient evidence, and known medication-safety considerations. It does not independently verify product identity, purity, potency, contamination, or manufacturing quality. How these ratings are computed

At a glance

General information

Key facts about L-Tryptophan, straight from the product label.

Brand Klaire Labs
Barcode (UPC) 817234010978
Net contents 90 Vegetarian Capsule(s)
Market status On market
Date entered into DSLD Dec 21, 2024
DSLD ID 322391
Product type Amino Acid/protein
Supplement form Capsule
Dietary claims / uses All Other
Intended target group(s) Adult (18 - 50 Years), Gluten Free, Dairy Free
From the label
Everything in this section is reproduced from the manufacturer’s own product label — it’s the label speaking, not HelloPharmacist. We show it so you can see exactly what the maker states; we don’t verify or endorse those statements.

Supplement Facts

The label details for L-Tryptophan by Klaire Labs, sourced from the NIH Dietary Supplement Label Database.

Supplement Facts

Daily Value (DV) Target Group(s):
Adults and children 4 or more years of age
Minimum serving Sizes:
2 Capsule(s)
Maximum serving Sizes:
4 Capsule(s)
Servings per container
22
UPC/BARCODE
817234010978
IngredientAmount% DV
L-Tryptophan2000 mg--

Other ingredients: Hydroxypropyl Methylcellulose, Water, Ascorbyl Palmitate, Microcrystalline Cellulose

Tap any ingredient to jump to its full detail below.

Label statements
These statements are the manufacturer’s wording, reproduced from the product label — the label is saying it, not HelloPharmacist. We don’t verify or endorse them.
Formulation

Free of the following common allergens: milk/casein, eggs, fish, shellfish, tree nuts, peanuts, wheat, gluten, soybeans, corn, and yeast. Contains no artificial colors, flavors, or preservatives.

Produced under a strict quality management system in compliance with Good Manufacturing Practices (GMPs) and third-party quality certifications.

Suggested/Recommended/Usage/Directions

Suggested Use: Adults: 2-4 capsules at bedtime or as directed by a healthcare professional.

Precautions

Do not use if shrinkwrap is broken or missing.

Caution: Not intended for use by children unless under the guidance of a physician.

If you are pregnant, trying to conceive, nursing, have a medical condition, or taking prescription drugs(including antidepressants such as MAOIs and SSRIs, and sedatives), consult your physician before using this product.

May cause drowsiness. Do not use with alcoholic beverages or before and while operating a motor vehicle or machinery.

Keep out of reach of children.

Storage

Store in a cool, dry place(59 degrees F-85 degrees F) away from direct light.

FDA Statement of Identity

Dietary supplement

General Statements

SFI

Is this label outdated? Report a formula or label change and our pharmacy team will review it.

See for yourself

L-Tryptophan by Klaire Labs label

The label scan from the NIH Dietary Supplement Label Database. Tap to enlarge.

L-Tryptophan label

Label images are published by the NIH Dietary Supplement Label Database for the version of this product on file. Always read your actual product label.

View the full label (PDF)
What’s inside

The Ingredients in L-Tryptophan by Klaire Labs

This is the 1 active ingredient this product is made of. Select it to open its full monograph.

Serving size2 Capsule(s) Dosage formCapsule Servings per container22 Amounts shown are per serving.

L-Tryptophan

Interacts with
394 drugs
2000 mg per serving

L-tryptophan is an essential amino acid the body uses to make serotonin and melatonin, and people take it to support sleep and mood. The evidence for...

L-Tryptophan monograph & interactions

Other (inactive) ingredients: Hydroxypropyl Methylcellulose, Water, Ascorbyl Palmitate, Microcrystalline Cellulose. These complete the product’s ingredient list but are not active constituents.

Interaction report

L-Tryptophan by Klaire Labs Drug Interactions

Want to check YOUR meds against L-Tryptophan?

Ask about interactions with your drugs in plain English — “Can I take it with lisinopril?” — and we find you the answer in seconds, ingredient by ingredient.

 Go to the checker
394Drugs
248 Major 146 Moderate

Ingredients driving the most interactions

L-Tryptophan 394

Individual Drug Interactions

The ingredients in L-Tryptophan interact with 394 drugs. Click any drug to see the details.

1 of the 1 ingredient in L-Tryptophan interact with drugs. Each result below shows which ingredient is responsible. L-Tryptophan

Each ingredient & the kinds of drugs it affects

For each ingredient in L-Tryptophan with known interactions, here are the types of medications it can affect. Open any type for the detail — or search your exact drug in the checker above.

L-Tryptophan2 drug types · 394 drugs

Cns Depressants

Theoretically, concomitant use of L-tryptophan with CNS depressants might cause additive sedative effects.
Clinical research shows that L-tryptophan can cause fatigue and drowsiness.

Likelihood Probable Evidence B
Serotonergic Drugs

Theoretically, combining L-tryptophan with serotonergic drugs might cause additive serotonergic effects.
L-tryptophan is a precursor to serotonin. Theoretically, combining serotonergic drugs with L-tryptophan might increase the risk of serotonergic side effects, including serotonin syndrome and cerebral vasoconstrictive disorders.

Likelihood Possible Evidence D
L-Tryptophan full monograph & interactions
The maker

Brand information

Manufacturer and brand details for L-Tryptophan, from the product label.

Klaire Labs

See all Klaire Labs products
Name
SFI USA
City
Reno
State
NV
ZipCode
89521
Web Address
Klaire.com
Pharmacist Counseling Corner

L-Tryptophan by Klaire Labs: Common Questions

Does L-Tryptophan by Klaire Labs interact with any medications?
Yes. Based on its ingredients, L-Tryptophan has a known interaction with 394 medications, including 248 rated major. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
L-Tryptophan contains a single active ingredient, and that one ingredient can interact with many different medications on its own. We check it against each medication and show the mechanism responsible.
Where does this information come from?
The product label data comes from the NIH Dietary Supplement Label Database (DSLD); the interaction data is built on the Natural Medicines database and reviewed by HelloPharmacist pharmacists.
What does L-tryptophan do in the body?
L-tryptophan is an amino acid — one of the building blocks your body uses to make serotonin and other brain chemicals that regulate mood, sleep, and other functions.
Can I take this if I'm on an antidepressant?
Not without checking with your pharmacist first. Antidepressants are serotonergic drugs, and combining them with L-tryptophan may raise serotonin to unsafe levels and trigger serotonin syndrome, a serious condition. Always verify your specific medication before starting.
Does L-tryptophan actually work for depression?
According to the evidence we have on file, L-tryptophan is rated as possibly ineffective for depression. The data doesn't support it as a reliable treatment for that condition.
Is L-tryptophan safe now, given the past contamination issues?
Modern L-tryptophan from reputable manufacturers is considered generally well tolerated. However, the 1989 contamination scare — in which a single Japanese producer caused over 1,500 cases of a rare nerve disorder — is part of its history. Stick with brands from trusted suppliers and mention this product to your pharmacist if you have concerns.
Can I take this while breastfeeding?
No — safety data for L-tryptophan during breastfeeding is not established, so it's best avoided. Talk to your doctor or pharmacist about safer options if you're nursing.
What are the most common side effects?
Most people who take L-tryptophan experience mild effects like drowsiness, nausea, diarrhea, headache, heartburn, stomach pain, or dry mouth. Serious side effects are rare with modern products, but the supplement can cause fatigue and drowsiness on its own.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

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Ask a pharmacist

Label information is sourced from the NIH Dietary Supplement Label Database and reflects the product version on file; always read your actual product label. This page is for education only and is not a substitute for professional medical advice. Confirm with your pharmacist or doctor before combining supplements and medications.

L-Tryptophan label
Go deeper

The Full Monographs Behind L-Tryptophan’s Ingredients

Every ingredient we hold a full HelloPharmacist monograph for — uses, evidence, safety, and the complete interaction list.

Herb & supplement monograph

L-tryptophan

Interacts with 394 drugs

L-tryptophan is an essential amino acid the body uses to make serotonin and melatonin, and people take it to support sleep and mood. The evidence for supplement use is limited and mixed, and...

Read the full L-tryptophan monograph →
Sources

Sources & How We Checked

L-Tryptophan's label data comes from the NIH Dietary Supplement Label Database; the ingredient interaction data is from the Natural Medicines database, reviewed by our pharmacists.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

The 18 references behind this product’s interaction data

Every citation that drives the interaction findings for this product’s ingredients, from the evidence-graded Natural Medicines (TRC Healthcare) database. Open an ingredient to browse its citations — links open the study on PubMed or the publisher’s site.

L-tryptophan 18 references
  1. Messiha FS. Fluoxetine: adverse effects and drug-drug interactions. J Toxicol Clin Toxicol 1993;31:603-30. PubMed
  2. Devoe LD, Castillo RA, Searle NS. Maternal dietary substrates and human fetal biophysical activity. The effects of tryptophan and glucose on fetal breathing movements. Am J Obstet Gynecol 1986;155:135-9. DOI
  3. Lieberman HR, Corkin S, Spring BJ. The effects of dietary neurotransmitter precursors on human behavior. Am J Clin Nutr 1985;42:366-70. PubMed
  4. U. S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, Office of Nutritional Products, Labeling, and Dietary Supplements. Information Paper on L-Tryptophan and 5-hydroxy-L-tryptophan, February 2001.
  5. Sullivan EA, Kamb ML, Jones JL, et al. The natural history of eosinophilia-myalgia syndrome in a tryptophan-exposed cohort in South Carolina. Arch Intern Med 1996;156:973-9. DOI
  6. Philen RM, Hill RH, Flanders WD, et al. Tryptophan contaminants associated with eosinophilia-myalgia syndrome. Am J Epidemiol 1993;138:154-9. PubMed
  7. Bohme A, Wolter M, Hoelzer D. L-tryptophan-related eosinophilia-myalgia syndrome possibly associated with a chronic B-lymphocytic leukemia. Ann Hematol 1998;77:235-8. PubMed
  8. Singhal AB, Caviness VS, Begleiter AF, et al. Cerebral vasoconstriction and stroke after use of serotonergic drugs. Neurology 2002;58:130-3. PubMed
  9. Priori R, Conti F, Luan FL, et al. Chronic fatigue: a peculiar evolution of eosinophilia myalgia syndrome following treatment with L-tryptophan in four Italian adolescents. Eur J Pediatr 1994;153:344-6..
  10. Klein R, Berg PA. A comparative study on antibodies to nucleoli and 5-hydroxytryptamine in patients with fibromyalgia syndrome and tryptophan-induced eosinophilia-myalgia syndrome. Clin Investig 1994;72:541-9.. PubMed
  11. Simat TJ, Kleeberg KK, Muller B, Sierts A. Synthesis, formation, and occurrence of contaminants in biotechnologically manufactured L-tryptophan. Adv Exp Med Biol 1999;467:469-80.. PubMed
  12. Shaw K, Turner J, Del Mar C. Tryptophan and 5-hydroxytryptophan for depression. Cochrane Database Syst Rev 2002;(1):CD003198. PubMed
  13. Kilbourne EM, Philen RM, Kamb ML, Falk H. Tryptophan produced by Showa Denko and epidemic eosinophilia-myalgia syndrome. J Rheumatol Suppl 1996;46:81-8.
  14. Horwitz RI, Daniels SR. Bias or biology: evaluating the epidemiologic studies of L-tryptophan and the eosinophilia-myalgia syndrome. J Rheumatol Suppl 1996;46:60-72.
  15. Shapiro S. Epidemiologic studies of the association of L-tryptophan with the eosinophilia-myalgia syndrome: a critique. J Rheumatol Suppl 1996;46:44-58.
  16. Mayeno AN, Gleich GJ. The eosinophilia-myalgia syndrome: lessons from Germany. Mayo Clin Proc 1994;69:702-4. PubMed
  17. Carr L, Ruther E, Berg PA, Lehnert H. Eosinophilia-myalgia syndrome in Germany: an epidemiologic review. Mayo Clin Proc 1994;69:620-5. PubMed
  18. Ullrich SS, Fitzgerald PCE, Giesbertz P, Steinert RE, Horowitz M, Feinle-Bisset C. Effects of intragastric administration of tryptophan on the blood glucose response to a nutrient drink and energy intake, in lean and obese men. Nutrients 2018;10(4). pii: PubMed

See these in context on the L-tryptophan monograph →

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

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