Herb & supplement monograph

L-tryptophan Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how L-tryptophan interacts with medications. The heart of this page is the interaction list — every drug L-tryptophan is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what L-tryptophan is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Reviewed by licensed pharmacists Sourced from Natural Medicines

On this page

Interaction report

Drugs that interact with L-tryptophan

394 medications have a known interaction with L-tryptophan, graded by severity. Select any drug for the full evidence-based detail.

248 major interactions. These combinations can be clinically significant — best avoided, or used only with close professional supervision. Always check with your pharmacist before combining them with L-tryptophan.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against L-tryptophan using our pharmacist-reviewed interaction data.

AI summaries are generated from our L-tryptophan interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
Possible. Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact L-tryptophan combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs L-tryptophan affects

Every type of medication (drug category) L-tryptophan is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 2 drug categories L-tryptophan interacts with

Cns DepressantsSerotonergic 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

Monograph

L-tryptophan: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

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 there are real safety concerns, so talk to a pharmacist or doctor before trying it.

Part used: Amino acid (made from dietary protein or by fermentation)
Common forms: Capsules, tablets, powder

People commonly use it for

Sleep problems
Low mood and depression
Anxiety
Premenstrual symptoms
Appetite and food cravings

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallUse caution

May cause mild side effects and has a past history of a contaminated-product safety scare.

PregnancyLikely Safe

When used orally in amounts commonly found in foods.

Read the full pregnancy detail

BreastfeedingLikely Safe

When used orally in amounts commonly found in foods. There is insufficient reliable information available about the safety of larger medicinal amounts...

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

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Overview

L-tryptophan is an essential amino acid, which means it is a building block of protein that your body cannot make on its own. You must get it from the foods you eat. It is found in many protein-rich foods such as poultry, eggs, dairy, fish, nuts, and seeds.

In the body, L-tryptophan is used to make serotonin, a brain chemical involved in mood and sleep, and melatonin, a hormone that helps control the sleep-wake cycle. Because of this, supplement makers sell it in capsule, tablet, and powder forms, often marketed for sleep and mood support.

How it works

L-tryptophan is a chemical precursor, meaning the body converts it into other substances. It is changed into 5-HTP and then into serotonin, a neurotransmitter that helps regulate mood, sleep, and appetite. Serotonin can also be further converted into melatonin, which helps signal the body that it is time to sleep.

The idea behind supplements is that taking extra tryptophan may raise serotonin and melatonin levels and therefore support mood and sleep. While this pathway is well understood in the lab, taking a supplement does not always translate into clear, predictable effects in people.

Effectiveness

Does L-tryptophan work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 18 uses evaluated

1 Leans ineffective 17 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

Possibly Ineffective Depression