Drug & supplement interaction

Melatonin + Aspirin, Codeine Phosphate, Phenobarbital

Aspirin, Codeine Phosphate, Phenobarbital brand name: Phenaphen.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Aspirin, Codeine Phosphate, Phenobarbital falls into 4 drug categories that Melatonin can interact with; the most serious is rated moderate. Theoretically, taking melatonin might increase the sedative effects of CNS depressants.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions4
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Melatonin and Aspirin, Codeine Phosphate, Phenobarbital

These two interact in 4 distinct ways. Each one is explained separately below.

Why Are There 4 Interactions?

Melatonin interacts with whole categories of medication. Aspirin, Codeine Phosphate, Phenobarbital falls into 4 of those categories, so it can interact with Melatonin in 4 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

CNS DEPRESSANTS

1 of 4

Why this applies to Aspirin, Codeine Phosphate, Phenobarbital

Aspirin, Codeine Phosphate, Phenobarbital falls under CNS DEPRESSANTS — the group Melatonin interacts with.

Theoretically, taking melatonin might increase the sedative effects of CNS depressants.
Melatonin has sedative effects. Theoretically, concomitant use of melatonin with alcohol, benzodiazepines, or other sedative drugs might cause additive sedation.
Severity Moderate Likelihood Possible Evidence D

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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

This combination product contains two ingredients that already make you drowsy: codeine (an opioid pain reliever) and phenobarbital (a barbiturate sedative). Melatonin gently signals your brain that it's bedtime, so stacking it on top can add to that sleepiness. The concern here is mainly extra drowsiness, grogginess, dizziness, or feeling foggy and slow, especially the morning after.

To be fair, this is a theoretical caution based on how these ingredients work, not strong real-world data, and many people use melatonin without trouble. Still, with phenobarbital and codeine in the mix, I'd be careful, avoid driving until you know how you feel, and check with your pharmacist or doctor before combining them.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Foster BC, Cvijovic K, Boon HS, et al. Melatonin Interaction Resulting in Severe Sedation. J Pharm Pharm Sci 2015;18(2):124-31. PubMed
Moderate

SEIZURE THRESHOLD LOWERING DRUGS

2 of 4

Aspirin, Codeine Phosphate, Phenobarbital also falls under SEIZURE THRESHOLD LOWERING DRUGS.

Theoretically, taking melatonin with drugs that lower the seizure threshold might increase the risk of seizure activity.
Some clinical evidence suggests that melatonin may increase the frequency of seizures in certain patients, particularly children with neurological disabilities.
Severity Moderate Likelihood Possible Evidence D

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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

This combo product mixes aspirin, codeine, and phenobarbital. Phenobarbital is the piece that matters here. It's a barbiturate, and ironically, even though it's used to control seizures, melatonin has been linked in some reports to a higher seizure frequency, mostly in children with neurological problems. So the concern isn't about how phenobarbital is broken down. It's that melatonin might nudge the seizure threshold in a way that could work against what this medicine is doing.

I want to be straight with you: this is mostly theoretical, based on how these things behave rather than solid proof. For most adults using a short-term sleep aid, it's likely a non-issue. Still, since phenobarbital is serious medicine, please run melatonin by your pharmacist or doctor first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Sheldon SH. Pro-convulsant effects of oral melatonin in neurologically disabled children. Lancet 1998;351:1254. PubMed
  2. Stewart LS. Endogenous melatonin and epileptogenesis: facts and hypothesis. Int J Neurosci 2001;107:77-85.. PubMed
Moderate

ANTICOAGULANT/ANTIPLATELET DRUGS

3 of 4

Aspirin, Codeine Phosphate, Phenobarbital also falls under ANTICOAGULANT/ANTIPLATELET DRUGS.

Theoretically, melatonin may have anticoagulant effects and may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
There are isolated case reports of minor bleeding and decreased prothrombin activity in people taking melatonin with warfarin (Coumadin). The mechanism, if any, of this interaction is unknown. Taking melatonin orally seems to decrease coagulation activity within one hour of dosing in healthy men.
Severity Moderate Likelihood Possible Evidence B

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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

This combination pill contains three things, but the part that matters here is the aspirin. Aspirin already thins the blood by making platelets less sticky, which is why it can raise bleeding risk on its own. Melatonin may have a mild blood-thinning effect too, so stacking the two could, in theory, nudge your bleeding risk a little higher.

Honestly, the evidence here is thin. It comes mostly from a few case reports (mostly with warfarin) and some lab signals, not strong studies. For most people taking occasional melatonin, this is unlikely to cause trouble. Still, watch for things like easy bruising, nosebleeds, bleeding gums, or dark stools, and check with your pharmacist or doctor before pairing them, especially if you bleed easily.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Herxheimer A, Petrie KJ. Melatonin for the prevention and treatment of jet lag. Cochrane Database Syst Rev 2002;2:CD001520. PubMed
  2. Wirtz, P. H., Spillmann, M., Bartschi, C., Ehlert, U., and von Kanel, R. Oral melatonin reduces blood coagulation activity: a placebo-controlled study in healthy young men. J Pineal Res 2008;44(2):127-133. PubMed
  3. U.S.Food and Drug Administration. Special Nutritionals Adverse Events Monitoring System: registered case reports.
Minor

CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES

4 of 4

Aspirin, Codeine Phosphate, Phenobarbital also falls under CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES.

Theoretically, melatonin might increase levels of drugs metabolized by CYP2D6.
Laboratory research suggests that certain lots of melatonin inhibit CYP2D6. Theoretically, combined administration of melatonin with certain drugs metabolized by the CYP2D6 enzyme may reduce the metabolism of these drugs, resulting in increased serum levels. Until more is known, use melatonin cautiously in patients taking drugs metabolized by these enzymes.
Severity Minor Likelihood Possible Evidence D

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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the wrinkle with this combo product: one of its ingredients, codeine, is a prodrug. Your body has to use an enzyme called CYP2D6 to turn codeine into morphine, which is what actually relieves pain. Lab studies hint that some batches of melatonin might block that same enzyme. If that happened in real life, less codeine would convert to morphine, so you could get less pain relief, not more.

I want to keep this in perspective. This is a theoretical, test-tube finding rated as minor, so for most people taking melatonin for sleep it's unlikely to be a big deal. Still, since both melatonin and codeine (plus the phenobarbital here) can make you drowsy, it's worth a quick chat with your pharmacist before pairing them.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Foster BC, Cvijovic K, Boon HS, et al. Melatonin Interaction Resulting in Severe Sedation. J Pharm Pharm Sci 2015;18(2):124-31. PubMed

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction 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.
  • PossibleInteraction 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.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Melatonin Also Interacts With Other Medications

Melatonin has 1,115 moderate, 345 minor known drug interactions in our database — the Aspirin, Codeine Phosphate, Phenobarbital one above is among them. If you take anything else, check it against the full list below.

Moderate 1,115 Minor 345 No known interaction 1,370 (incl. Aspirin, Codeine Phosphate, Phenobarbital)
Taking anything else?

Check Another of Your Medications Against Melatonin

Covers the 2,830 medications we’ve checked against Melatonin. Pick one to open its full report.

From our Q&A

Questions About Melatonin or Aspirin, Codeine Phosphate, Phenobarbital

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Melatonin or Aspirin, Codeine Phosphate, Phenobarbital, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Aspirin, Codeine Phosphate, Phenobarbital

This page covers Melatonin only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Aspirin, Codeine Phosphate, Phenobarbital page lists 352 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: 1,4-butanediol (major), Activated Charcoal (major), Asarabacca (major), Beer (major) and Danshen (major).

By severity: 12 major · 304 moderate · 36 minor.

From our pharmacist’s overview on the Aspirin, Codeine Phosphate, Phenobarbital page

“Alcohol is the entry I would flag first with Phenaphen (aspirin, codeine phosphate, phenobarbital): beer or wine layered onto codeine and phenobarbital can deepen sedation and, at worst, slow breathing. This medication deserves real caution with supplements.”

Reviewed by 2 · Jul 18, 2026

Open the Aspirin, Codeine Phosphate, Phenobarbital interaction page

One more smart check

Taking Melatonin as Part of a Dietary Supplement Product? Check It for Interactions

We hold 2,885 real supplement products containing Melatonin, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Melatonin. Your product may carry other ingredients that interact with Aspirin, Codeine Phosphate, Phenobarbital too, on top of Melatonin — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Melatonin and Aspirin, Codeine Phosphate, Phenobarbital Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Melatonin
Top 5%

#54 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Aspirin, Codeine Phosphate, Phenobarbital
Top 25%

#504 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Melatonin

What is Melatonin?

Melatonin
  • Trouble falling asleep (insomnia)
  • Jet lag
  • Delayed sleep phase syndrome
  • Non-24-hour sleep-wake disorder
  • Shift-work sleep problems
  • Sleep problems in some children with conditions like autism or ADHD

Melatonin is a hormone your body makes naturally to help control your sleep-wake cycle, and the supplement form is widely used to help with sleep timing problems and jet lag. The evidence is strongest for certain circadian (body-clock) disorders and is more mixed for everyday insomnia. It is generally well tolerated for short-term use, but talk with your pharmacist or doctor before starting, especially for children or during pregnancy.

Read the full Melatonin monograph & all interactions
Keep checking

Other Drugs & Melatonin

Browse every other medication we’ve checked against Melatonin — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
1,115Moderate
345Minor
1,369No known interaction
1,115 Moderate 345 Minor 1,369 No interaction
Moderate

1,115 interactions

Showing 60 of 1,115 moderate interactions — see all 1,115 on the Melatonin page.

Minor

345 interactions

Showing 60 of 345 minor interactions — see all 345 on the Melatonin page.

No interaction 1,369 drugs checked — show the list

We also checked Melatonin against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 1,369 medications checked with no known interaction — see the full Melatonin list.

See the full Melatonin interactions page
See every supplement checked against Aspirin, Codeine Phosphate, Phenobarbital, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

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

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

Keep exploring
Melatonin monograph › Uses, safety, and every drug interaction in one place Aspirin, Codeine Phosphate, Phenobarbital supplement interactions › Every supplement checked against Aspirin, Codeine Phosphate, Phenobarbital, ranked by severity Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Melatonin and Aspirin, Codeine Phosphate, Phenobarbital Together: Common Questions

Can you take Melatonin with Aspirin, Codeine Phosphate, Phenobarbital?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
Why are there 4 interactions listed for Melatonin and Aspirin, Codeine Phosphate, Phenobarbital?
Aspirin, Codeine Phosphate, Phenobarbital belongs to more than one drug category, and Melatonin interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the Melatonin and Aspirin, Codeine Phosphate, Phenobarbital interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

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

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.