Drug & supplement interaction

Melatonin + Aspirin, Diphenhydramine, Phenylpropanolamine

Aspirin, Diphenhydramine, Phenylpropanolamine brand name: Alka Seltzer Plus Night Time Effervescent.

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

Aspirin, Diphenhydramine, Phenylpropanolamine falls into 3 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
Interactions3
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Melatonin and Aspirin, Diphenhydramine, Phenylpropanolamine

These two interact in 3 distinct ways. Each one is explained separately below.

Why Are There 3 Interactions?

Melatonin interacts with whole categories of medication. Aspirin, Diphenhydramine, Phenylpropanolamine falls into 3 of those categories, so it can interact with Melatonin in 3 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 3

Why this applies to Aspirin, Diphenhydramine, Phenylpropanolamine

Aspirin, Diphenhydramine, Phenylpropanolamine 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

Here's the thing to watch with this combo product: that Alka-Seltzer Plus Night Time already contains diphenhydramine, the same drowsy-making antihistamine found in many sleep aids. Melatonin sends its own "time to wind down" signal, so stacking the two can pile on the sleepiness. This is mostly a theory based on how both work, not something proven in big studies, but it makes good sense.

What could that feel like? More grogginess, heavier next-morning fog, dizziness, or feeling unsteady on your feet, which matters most for older folks or if you need to drive. Honestly, since the diphenhydramine alone usually does the job for nighttime relief, adding melatonin may just be overkill. Check 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
Moderate

SEIZURE THRESHOLD LOWERING DRUGS

2 of 3

Aspirin, Diphenhydramine, Phenylpropanolamine 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 (Alka-Seltzer Plus Night Time) contains diphenhydramine, an antihistamine that, at high doses, can slightly lower the seizure threshold (meaning it can make seizures a little more likely in people who are already prone to them). The idea here is that melatonin might add to that effect. I want to be honest with you though: this concern is theoretical, based on how these things work rather than on solid studies in everyday adults.

The main signal comes from a specific group, children with neurological disabilities, where melatonin sometimes increased seizure frequency. For most healthy adults using this for a cold and occasional sleep, the everyday risk is low. If you or your child has a seizure disorder, please check with your pharmacist or doctor before combining them.

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 3

Aspirin, Diphenhydramine, Phenylpropanolamine 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 combo product contains aspirin, which is the piece that matters here. Aspirin already thins your blood by making your platelets less sticky. Melatonin may have a mild blood-thinning effect of its own, so pairing the two could, in theory, add up and raise your chance of bleeding or bruising. That might show up as easy bruising, nosebleeds, bleeding gums, or a stomach upset that lasts longer than usual.

I want to be honest that this is mostly theoretical. It comes from a few scattered case reports and small studies, not strong proof, so for occasional short-term use it's usually not a big deal. Still, if you bruise easily, take other blood thinners, or notice any unusual bleeding, check in with your pharmacist or doctor first.

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.

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, Diphenhydramine, Phenylpropanolamine 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, Diphenhydramine, Phenylpropanolamine)
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, Diphenhydramine, Phenylpropanolamine

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, Diphenhydramine, Phenylpropanolamine, 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, Diphenhydramine, Phenylpropanolamine

This page covers Melatonin only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Aspirin, Diphenhydramine, Phenylpropanolamine page lists 361 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: 17 major · 308 moderate · 36 minor.

From our pharmacist’s overview on the Aspirin, Diphenhydramine, Phenylpropanolamine page

“A cold remedy used for a few nights can still collide with supplements taken daily, and Alka Seltzer Plus Night Time (aspirin, diphenhydramine, phenylpropanolamine) is one to treat with genuine care. Its three ingredients thin the blood, sedate, and stimulate all at once, which is why 361 supplements and herbs are on file here.”

Reviewed by 2 · Jul 18, 2026

Open the Aspirin, Diphenhydramine, Phenylpropanolamine 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, Diphenhydramine, Phenylpropanolamine 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, Diphenhydramine, Phenylpropanolamine 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%

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

29 days ago today
Medication Aspirin, Diphenhydramine, Phenylpropanolamine
Top 25%

#532 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, Diphenhydramine, Phenylpropanolamine, 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, Diphenhydramine, Phenylpropanolamine supplement interactions › Every supplement checked against Aspirin, Diphenhydramine, Phenylpropanolamine, 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, Diphenhydramine, Phenylpropanolamine Together: Common Questions

Can you take Melatonin with Aspirin, Diphenhydramine, Phenylpropanolamine?
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 3 interactions listed for Melatonin and Aspirin, Diphenhydramine, Phenylpropanolamine?
Aspirin, Diphenhydramine, Phenylpropanolamine 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, Diphenhydramine, Phenylpropanolamine 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

Still Have a Question About Aspirin, Diphenhydramine, Phenylpropanolamine and Melatonin?

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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.