Drug & supplement interaction

Methylsynephrine + Promethazine

Promethazine brand name: Phenergan.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 20, 2026
The bottom line No known interaction

We found no known interaction between Methylsynephrine and Promethazine in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

Methylsynephrine and Promethazine

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Promethazine and Methylsynephrine in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Methylsynephrine safety at a glance

Methylsynephrine overall Avoid It is a stimulant drug not approved as a supplement and has been tied to serious cardiovascular events.
Pregnancy Avoid Stimulant with unknown safety; should not be used during pregnancy.
Breastfeeding Avoid No safety data; avoid while breastfeeding.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Promethazine and Methylsynephrine? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Promethazine

Interactions in our licensed database are recorded against drug classes, not just single drug names. Promethazine is filed under 4 classifications — including phenothiazines, anticholinergic drugs, photosensitizing drugs. Methylsynephrine has documented interactions with 2 drug classes — the most serious being beta-adrenergic agonists (moderate) and stimulant drugs (moderate) — and none of Promethazine’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Methylsynephrine Does Interact With Other Medications

Methylsynephrine has 191 moderate known drug interactions in our database — Promethazine isn’t one of them. If you take anything else, check it against the full list below.

Moderate 191 No known interaction 2,639 (incl. Promethazine)
Taking anything else?

Check Another of Your Medications Against Methylsynephrine

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

What to actually watch for

No Interaction Found — But Data Suggests Methylsynephrine and Promethazine May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do.

  • A fast or pounding heartbeat Additional detail

    Methylsynephrine

    “There is currently a limited amount of information available about the adverse effects of methylsynephrine. Orally, it has been reported to cause increased blood pressure, palpitations, and arrhythmia.”

    Methylsynephrine · Natural Medicines adverse-effect record, reported in arrhythmia.

    2 sources cited
    1. 94386. Pawar RS, Grundel E. Overview of regulation of dietary supplements in the USA and issues of adulteration with phenethylamines (PEAs). Drug Test Anal 2017;9:500-517. PubMed
    2. 99910. Cohen PA, Avula B, Venhuis B, Travis JC, Wang YH, Khan IA. Pharmaceutical doses of the banned stimulant oxilofrine found in dietary supplements sold in the USA. Drug Test Anal. 2017;9(1):135-142. PubMed

    “Orally, methylsynephrine has been reported to cause increased blood pressure, palpitations, and arrhythmias.

    In the Netherlands, the supplement dexaprine was removed from the market because of reported cases of tachycardia, palpitations, chest pain, and a single report of cardiac arrest. As little as half a tablet was associated with these adverse effects, which occurred within one hour of ingestion.”

    Methylsynephrine · Natural Medicines adverse-effect record, reported in arrhythmia.

    3 sources cited
    1. 94386. Pawar RS, Grundel E. Overview of regulation of dietary supplements in the USA and issues of adulteration with phenethylamines (PEAs). Drug Test Anal 2017;9:500-517. PubMed
    2. 99910. Cohen PA, Avula B, Venhuis B, Travis JC, Wang YH, Khan IA. Pharmaceutical doses of the banned stimulant oxilofrine found in dietary supplements sold in the USA. Drug Test Anal. 2017;9(1):135-142. PubMed
    3. 99913. Venhuis B, Keizers P, van Riel A, de Kaste D. A cocktail of synthetic stimulants found in a dietary supplement associated with serious adverse events. Drug Test Anal. 2014;6(6):578-81. PubMed

    Promethazine

    Listed in the ADVERSE REACTIONS section of the FDA label for Promethazine. Read the label on DailyMed ›

  • Vomiting / Nausea reported in 11.7% of FDA reports for Promethazine Additional detail

    Methylsynephrine

    “In the Netherlands, the supplement dexaprine was removed from the market following reported cases of nausea and vomiting. As little as half a tablet was associated with these adverse effects, which occurred within one hour of ingestion. Dexaprine was found to contain methylsynephrine, synephrine, deterenol, yohimbine, caffeine, theophylline, and possibly beta-methyl-beta-phenylethylamines.”

    Methylsynephrine · Natural Medicines adverse-effect record, reported in nausea and vomiting.

    1 source cited
    1. 99913. Venhuis B, Keizers P, van Riel A, de Kaste D. A cocktail of synthetic stimulants found in a dietary supplement associated with serious adverse events. Drug Test Anal. 2014;6(6):578-81. PubMed

    Promethazine

    Listed in the ADVERSE REACTIONS section of the FDA label for Promethazine, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›

Reported for Methylsynephrine but not commonly for Promethazine: raised blood pressure, an irregular heartbeat and chest pain.

Effects for Promethazine come from the ADVERSE REACTIONS section of its FDA label; effects for Methylsynephrine come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 22,361 voluntary FDA FAERS reports for Promethazine that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

From our Q&A

Questions About Methylsynephrine or Promethazine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Methylsynephrine or Promethazine, 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 Promethazine

This page covers Methylsynephrine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Promethazine page lists 83 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Henbane (major), Scopolia (major), Alfalfa (moderate) and Angel's Trumpet (moderate).

By severity: 3 major · 57 moderate · 23 minor.

From our pharmacist’s overview on the Promethazine page

“Promethazine (Phenergan) is a phenothiazine antihistamine used for allergies, nausea, and motion sickness, and it is strongly anticholinergic on its own, causing dry mouth, blurred vision, drowsiness, and constipation. That is why the 83 supplements and herbs on this list deserve real attention, starting with the three rated major.”

Reviewed by 2 · Jul 18, 2026

Open the Promethazine interaction page

One more smart check

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

We hold 55 real supplement products containing Methylsynephrine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Methylsynephrine. Even though Methylsynephrine itself has no known interaction with Promethazine, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Methylsynephrine and Promethazine 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 Methylsynephrine
Top half

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

29 days ago today
Medication Promethazine
Steady interest

#2,040 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.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Methylsynephrine reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Methylsynephrine and Promethazine records this page draws on were last updated July 10, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Supplement

About Methylsynephrine

What is Methylsynephrine?

  • Weight loss and fat burning
  • Boosting energy
  • Athletic and workout performance
  • Appetite control

Methylsynephrine (also called oxilofrine) is a synthetic stimulant sometimes added to weight-loss and pre-workout products, but it is not a legal or approved dietary ingredient in the United States. It has been linked to serious heart and blood pressure problems, and there is no good evidence it is safe or effective for these uses, so it is best avoided.

Synthetic compound (also reported in some Citrus species) · Capsules, tablets, powders (mostly in weight-loss and pre-workout supplements)

An interaction check asks whether these two react with each other — it does not ask whether Methylsynephrine is a good idea for someone in your situation. Here is what our Methylsynephrine record says about it on its own.

Methylsynephrine: dosing

There is no established safe or approved dose of methylsynephrine for use as a dietary supplement, and we will not suggest one. It is not a legal supplement ingredient in the United States.Supplement labels may list it under different names (such as oxilofrine or methylsynephrine) and amounts can be inconsistent or unreliable. The safest choice is to avoid products that contain it.

From our Methylsynephrine monograph — the full record covers uses, side effects and every documented interaction.

Read the full Methylsynephrine monograph & all interactions
Medication

About Promethazine

What Is Promethazine Used For?

Brand name: Phenergan

Promethazine is used for a wide range of conditions. Tablets, oral solution, and rectal suppositories (brands including Phenergan, Promethegan, and Phenadoz) are approved for seasonal and perennial allergic rhinitis, vasomotor rhinitis, allergic conjunctivitis, hives (urticaria), angioedema, dermographism, and allergic reactions to blood or plasma. They are also used for motion sickness (both prevention and active treatment), nausea and vomiting related to anesthesia and surgery, sedation, and as a helper medication alongside pain relievers after surgery.

Promethazine hydrochloride injection (brands including Phenergan and Promethazine HCl injection) is used for many of the same purposes but is reserved for situations where oral treatment is not possible — including allergic emergencies as an adjunct to epinephrine, sedation during labor, and as an aid during certain surgical procedures such as bronchoscopy and eye surgery.

Most-Reported Side Effects for Promethazine

From FAERS, the FDA’s public side-effect reporting system (22,614 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Dependence 3,586 reports
Nausea 2,646 reports
Vomiting 1,802 reports
Fatigue 1,496 reports
Diarrhea 1,341 reports
See full Promethazine drug information
Keep checking

Other Drugs & Methylsynephrine

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

0Major
191Moderate
0Minor
2,638No known interaction
191 Moderate 2,638 No interaction
Moderate

191 interactions

Showing 60 of 191 moderate interactions — see all 191 on the Methylsynephrine page.

No interaction 2,638 drugs checked — show the list

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

Showing the 60 most looked-up of 2,638 medications checked with no known interaction — see the full Methylsynephrine list.

See the full Methylsynephrine interactions page
See every supplement checked against Promethazine, ranked by severity
Evidence & sources

Methylsynephrine References

The 3 references that drive our Methylsynephrine monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Pawar RS, Grundel E. Overview of regulation of dietary supplements in the USA and issues of adulteration with phenethylamines (PEAs). Drug Test Anal 2017;9:500-517. PubMed
  2. Cohen PA, Avula B, Venhuis B, Travis JC, Wang YH, Khan IA. Pharmaceutical doses of the banned stimulant oxilofrine found in dietary supplements sold in the USA. Drug Test Anal. 2017;9(1):135-142. PubMed
  3. Venhuis B, Keizers P, van Riel A, de Kaste D. A cocktail of synthetic stimulants found in a dietary supplement associated with serious adverse events. Drug Test Anal. 2014;6(6):578-81. PubMed

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Methylsynephrine and Promethazine Together: Common Questions

Is it safe to take Methylsynephrine with Promethazine?
We do not list a known interaction between Methylsynephrine and Promethazine. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Do Methylsynephrine and Promethazine have any of the same side effects?
Yes — our sources link each of them separately to 3 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.
How was the Methylsynephrine and Promethazine combination checked?
Interactions in our licensed database are recorded against drug classes. Promethazine is filed under 4 classifications, and Methylsynephrine has documented interactions with 2 drug classes — none of Promethazine's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.
Does Methylsynephrine interact with any other medications?
Yes. Methylsynephrine has 191 documented drug interactions in our database — Promethazine is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.
Does Promethazine interact with any supplements?
Yes. Promethazine has documented interactions with 83 supplements in our database — Methylsynephrine is not one of them. The Promethazine interaction page linked on this page lists every one, ranked by severity.

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

Where next

Keep Exploring

Methylsynephrine monograph Uses, safety profile, and every drug interaction in one place Promethazine drug information The full plain-English guide to this medication Promethazine supplement interactions Every supplement checked against Promethazine, 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 References The 3 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Promethazine and Methylsynephrine?

Our pharmacists answer your medication & supplement questions — free.

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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.