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Dietary supplement

L-Tryptophan Powder Ingredients & Drug Interactions

by NOW

L-Tryptophan Powder label
See full label image
Powder 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 Powder 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 Powder is a dietary supplement by NOW 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 Powder by NOW

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

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HelloPharmacist Scorecard of L-Tryptophan Powder by NOW

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 Aug 13, 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 powder contains one active ingredient: L-tryptophan, an amino acid your body uses to make serotonin and melatonin — chemicals that influence mood and sleep. The only other ingredient is cellulose, an inactive filler.

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: supports positive mood and healthy sleep.
  • We looked for evidence on: Anxiety, Depression, Seasonal affective disorder (SAD), Premenstrual dysphoric disorder (PMDD), Premenstrual syndrome (PMS), insomnia — 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).

L-tryptophan is rated possibly ineffective for depression based on the evidence we hold. For anxiety, athletic performance, teeth grinding (bruxism), and premenstrual dysphoric disorder, the evidence is too sparse to say whether it works.

The science simply isn't solid enough yet to make a real claim either way.

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 when taken by mouth. Common side effects include belching, diarrhea, drowsiness, dry mouth, gas, headache, heartburn, lightheadedness, nausea, stomach pain, blurred vision, and vomiting.

Rare serious concerns exist because of a contamination scare in the late 1980s — a Japanese manufacturer produced batches linked to eosinophilia-myalgia syndrome (EMS), a neurological disorder affecting the muscles and skin. About 95% of cases traced back to that one source, and L-tryptophan products were recalled and restricted in the U.S. afterward.

Modern products are much safer, but the history means you should use it cautiously. For pregnancy, safety data is mixed — some sources call it likely safe, others possibly unsafe; talk with your doctor about whether it's right for you.

Breastfeeding safety is not established, so it's best avoided while nursing.

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.

Double-check with your doctor or pharmacist before using this product if you take CNS depressants (sleep aids, sedatives, opioids, alcohol) or serotonergic drugs (certain antidepressants and migraine medications). Both interactions carry real risk and need a professional review of your specific medications.

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 is an amino acid supplement that may help some people with sleep and mood, though the evidence for depression is weak and for other uses is thin. If you take CNS depressants or serotonergic drugs, you need to clear it with your doctor or pharmacist first — the interactions can be serious.

Pregnant or nursing? Discuss it with your healthcare provider before starting.

The product itself is generally well tolerated if you're a good fit for it.

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 Nov 24, 2015.

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 Powder, straight from the product label.

Brand NOW
Barcode (UPC) 733739002631
Net contents 2 oz.; 57 Gram(s)
Market status On market
Date entered into DSLD Nov 24, 2015
DSLD ID 53458
Product type Amino Acid/protein
Supplement form Powder
Dietary claims / uses All Other, Structure/Function
Intended target group(s) Vegan, Vegetarian, 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 Powder by NOW, 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 tsp
Maximum serving Sizes:
2 tsp
Servings per container
57
UPC/BARCODE
733739002631
IngredientAmount% DV
L-Tryptophan950 mg--

Other ingredients: 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.
Seals/Symbols

GMP QUALITY ASSURED

Non-GMO

General Statements

Amino Acids

Family owned since 1968.

L-Tryptophan is an essential amino acid; therefore, it is not synthesized by the body and must be obtained from the diet. L-Tryptophan is critical for the production of serotonin and melatonin, which help to support a positive mood, healthy sleep patterns, and proper immune system function.*

Supports Relaxation*

~ Encourages Positive Mood* ~ Promotes Restful Sleep*

This product is sold by weight not volume.

Please Recycle.

Suggested/Recommended/Usage/Directions

Suggested Usage: Take one or two 1/4 level teaspoons 2 to 3 times daily on an empty stomach, with final dose at bedtime, or as directed by your physician.

Formulation

Every lot of NOW L-Tryptophan is tested to be free of Peak E and microbial contamination.

Vegetarian/Vegan

Not manufactured with wheat, gluten, soy, milk, egg, fish, shellfish or tree nut ingredients.

Precautions

Caution: For adults only.

Consult physician if pregnant/nursing, taking medication (especially antidepressants such as SSRIs or MAOIs), or have a medical condition.

May cause drowsiness. Do not use with alcoholic beverages or while operating heavy machinery.

Keep out of reach of children.

Do Not Eat Freshness Packet Enclosed.

Not manufactured with wheat, gluten, soy, milk, egg, fish, shellfish or tree nut ingredients. Produced in a GMP facility that processes other ingredients containing these allergens.

General

CODE 0263 V6

FDA Statement of Identity

A Dietary Supplement

Storage

Store in a cool, dry place after opening.

FDA Disclaimer Statement

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.

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

See for yourself

L-Tryptophan Powder by NOW label

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

L-Tryptophan Powder 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 Powder by NOW

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

Serving size2 tsp Dosage formPowder Servings per container57 Amounts shown are per serving.

L-Tryptophan

Interacts with
394 drugs
950 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: Cellulose. These complete the product’s ingredient list but are not active constituents.

Interaction report

L-Tryptophan Powder by NOW Drug Interactions

Want to check YOUR meds against L-Tryptophan Powder?

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 Powder interact with 394 drugs. Click any drug to see the details.

1 of the 1 ingredient in L-Tryptophan Powder 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 Powder 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 Powder, from the product label.

NOW

See all NOW products
Name
NOW Foods
Street Address
395 S. Glen Ellyn Rd.
City
Bloomingdale
State
IL
ZipCode
60108
Web Address
nowfoods.com
Pharmacist Counseling Corner

L-Tryptophan Powder by NOW: Common Questions

Does L-Tryptophan Powder by NOW interact with any medications?
Yes. Based on its ingredients, L-Tryptophan Powder 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 Powder 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 is L-tryptophan and what does it do?
L-tryptophan is an amino acid — a building block your body uses to make serotonin and melatonin, two brain chemicals tied to mood and sleep. You get small amounts from foods like turkey and nuts, but this supplement gives you a concentrated dose.
Can I take this if I'm pregnant?
The safety data on L-tryptophan in pregnancy is mixed — some sources say it's likely safe, others suggest it may not be. You need to talk with your doctor or midwife before taking it to decide what's right for your situation.
What are the most common side effects?
Belching, diarrhea, drowsiness, dry mouth, gas, headache, heartburn, lightheadedness, nausea, stomach pain, blurred vision, and vomiting. Most people tolerate it well, but your stomach or head might feel a bit off.
Is this the same product that was recalled in 1989?
No. That recall involved L-tryptophan contaminated by a single Japanese manufacturer — about 95% of the sickness cases traced back to that one source. Modern L-tryptophan products, including this one, have not been implicated, but the history is why we note using it cautiously.
Does it really help with depression?
The evidence says it's possibly ineffective for depression based on what we know. For anxiety, sleep, athletic performance, and other uses, there isn't enough solid research to say whether it works.
Can I take this with my sleep medication?
Not without checking first. L-tryptophan causes drowsiness and can add to the sedating effects of sleep aids and other CNS depressants — a Major interaction. Your doctor or pharmacist needs to review your specific medications.

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

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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 Powder label
Go deeper

The Full Monographs Behind L-Tryptophan Powder’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 Powder'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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